Hba1c in the Diagnosis of Type 2 Diabetes: a Systematic Review

HbA1c in the diagnosis of type 2 diabetes: a systematic review

Introduction

The use of HbA1c for diagnosis of type 2 diabetes is not currently recommended by the World Health Organization (WHO) (WHO 2006). The reasons cited in the 2006 report included that HbA1c measurement was not widely available in many countries throughout the world, global consistency in its measurement was problematic, and that the HbA1c result is influenced by several factors including anaemia and abnormalities of haemoglobin.

There is now renewed interest in HbA1c as a diagnostic criterion for diabetes. Consequently this systematic review was undertaken to address this question.

Research Question How does HbA1c perform in the diagnosis of type 2 diabetes based on the detection and prediction of microvascular complications?

Methods

OBJECTIVE To review best available evidence on the performance of HbA1c for the diagnosis of diabetes, based on the detection and prediction of microvascular complications.

CRITERIA FOR CONSIDERING STUDIES FOR THIS REVIEW Type of study Cohort studies evaluating the association between HbA1c levels and prevalent or incident microvascular complications.

Case-report, case-control and case-series studies and letters or commentaries were excluded.

Type of participants Adults aged 18 years and older with or without diabetes.

Types of outcome measures The following outcomes were included:

Main outcome • HbA1c cut-point associated with prevalent or incident microvascular complications associated with diabetes (e.g. retinopathy, microalbuminuria) • Acceptable forms of analyzing data on this association including sensitivity and specificity, ROC curve analysis, change point analysis, inspection of decile/vigintile distribution, and inspection of continuous plots. • Preference was given to studies using the most recent WHO diagnostic criteria, however studies using older WHO or ADA diagnostic criteria were also included.

Other outcomes

1 • FPG and 2-h PG cut-points associated with prevalent or incident microvascular complications (e.g. retinopathy, microalbuminuria) • Sensitivity and specificity, ROC curve analysis, change point analysis, inspection of decile/vigintile distribution, and inspection of continuous plots describing the association between HbA1c, FPG or 2-h PG values and prevalent or incident microvascular complications

Search methods for identification of studies

Electronic searches Databases were searched for relevant articles published between January 1990 and September 2010. The January 1990 start date was selected because HbA1c measurement was first developed in the late 70’s, did not become routinely used in clinical practice until the late 80’s and the first reports relevant to this review were published in the mid-90’s.

The following databases were searched: • Medline • Embase • Pubmed • Cinahl • Psycinfo • The Cochrane Library

A separate search strategy, specific for each electronic database was used for each search. These searches can be found in Appendix 1.

Searching was carried out using a combination of keywords that cover all relevant terminology for type 2 diabetes and the MESH terms HbA1c, type 2 diabetes, diagnosis and complications. These searches were supplemented by reviewing reference lists of relevant articles.

The relevance of articles was determined according to the inclusion and exclusion criteria. • Inclusion criteria require that the articles were conducted in humans (aged ≥ 18 years), contained cohorts with prevalent or incident cases of undiagnosed or newly diagnosed type 2 diabetes, with diagnosis of diabetes based on the oral glucose tolerance test (OGTT) or fasting plasma glucose (FPG) (using WHO 2006 or other established criteria); published in any language. • Exclusion criteria were letters, commentaries, time series, case reviews or case- control studies; all included participants had known diabetes.

METHODS OF THE REVIEW Data Collection and analysis The inclusion of studies was assessed independently by two assessors. Articles were only rejected on the initial screen if: • the reviewer could determine from the title and abstract that the article was a time series or case review or case-control study or letter or commentary;

2 • the study did not include measured HbA1c values • the study did not report prevalent or incident microvascular complications

When a title/abstract could not be rejected with certainty, the full text of the article was obtained for further evaluation.

Data abstraction was performed independently. Differences between reviewer’s results were resolved by discussion and reanalysis of studies and by returning to the relevant literature. A third reviewer was available to resolve any disagreement.

Assessing Study Quality and Level of Evidence Methodological quality of each study was assessed according to the Australian National Health and Medical Research Council (NHMRC) criteria for assessing study quality and grading the level of evidence (Appendix 2).

Quality assessment was not used as an exclusion criterion.

The GRADE (Grading of Recommendations Assessment, Development and Evaluation) program was also used to generate summary of findings tables (Schunemann et al. 2008).

Results The search strategy identified 9680 studies. The majority of these were found to be irrelevant upon reading the title, requiring only 134 abstracts to be read. Of these, 11 met the inclusion criteria and were included in the review. A summary of reviewed studies is detailed below and is summarised in the attached Tables.

HbA1c and the detection of prevalent microvascular complications McCance and colleagues (1994) performed a cross-sectional analysis of FPG, 2h plasma glucose (PG) and HbA1c and the presence of microvascular complications (retinopathy and nephropathy) associated with type 2 diabetes in Pima Indians aged ≥25 years (n=960) who were not receiving insulin or oral hypoglycaemic treatment at baseline. The cut-points which achieved maximum sensitivity and specificity for detecting retinopathy were ≥ 7.2 mmol/L for FPG (sensitivity 81%, specificity 80%), ≥ 13.0 mmol/L for 2h PG (sensitivity 88%, specificity 81%), and ≥ 7.0% for HbA1c (sensitivity 78%, specificity 85%). Cut-points that were equivalent to the WHO 2h PG criterion of ≥ 11.1 mmol/L (sensitivity 88%, specificity 76%) for detecting retinopathy were ≥ 6.8 mmol/L for FPG (sensitivity 81%, specificity 77%) and ≥ 6.1% for HbA1c (sensitivity 81%, specificity 77%). The prevalence of type 2 diabetes detected using the optimal cut-points for FPG was 22%, 2 h PG 21% and for HbA1c 17%. The areas under the curve for nephropathy were not as good as those for retinopathy.

Engelgau et al. (1997) performed a cross-sectional study of 1,018 Egyptians aged ≥ 20 years to compare FPG, 2h PG and HbA1c for diagnosing type 2 diabetes and to evaluate the performance of the WHO 1980 criteria. Of this population, 27% had known diabetes (91% of whom were receiving antihyperglycaemic medication) and 8% had undiagnosed diabetes. Cut-points for each glycaemic measure were calculated for OGTT defined diabetes as 1) the upper component of the fitted bimodal distribution for each glycaemic measure, and 2) the presence of diabetic retinopathy.

3 The point of intersection of the lower and upper components that minimised misclassification were ≥ 7.2 mmol/L for FPG, ≥ 11.5 mmol/L for 2h PG, and ≥ 6.7% for HbA1c. The sensitivities for FPG, 2h PG and HbA1c were 84%, 90%, and 68%, respectively; the specificities were all 100%. The prevalence of retinopathy increased above the sixth decile for FPG values (median glucose 6.6 mmol/L in seventh decile) and above the seventh decile for 2h PG (median glucose 14.4 mmol/L in eight decile) and HbA1c (median HbA1c 7.6% in eight decile) values. When diabetic retinopathy was used to define type 2 diabetes in the entire population, area under the receiver operator characteristic curve (AROC) analysis revealed that both FPG (0.85) and 2h PG (0.86) were superior to HbA1c (0.82; p < 0.01). In the total population, the sensitivity and specificity for detecting diabetic retinopathy were approximately equal for FPG, 2h PG and HbA1c cut-points of ≥ 7.8 mmol/l, ≥ 12.8 mmol/L, and ≥ 6.9%, respectively.

In an analysis of NHANES III data on 2,821 individuals aged 40-74 years in whom FPG, 2h PG and HbA1c were measured, all three measurements were strongly associated with retinopathy (The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus 1997). The prevalence of type 2 diabetes increased in the highest decile of each variable, corresponding to FPG ≥ 6.7 mmol/L, 2h PG ≥ 10.8 mmol/L, and HbA1c ≥ 6.2%.

Miyazaki and colleagues (2004) compared FPG, 2h PG and HbA1c to diagnose type 2 diabetes based on the prevalence of retinopathy in a Japanese population of 1,637 subjects aged 40-79 years from the Hisayama study. Of these subjects, 2.3% had diabetic retinopathy. All three measures were strongly associated with retinopathy. The prevalence of retinopathy dramatically increased in the tenth decile of each variable, corresponding to an FPG of ≥ 6.5 mmol/L, a 2h PG ≥ 11.0 mmol/L, and an HbA1c of ≥ 5.8%. The prevalence of retinopathy in the tenth decile of FPG, 2h PG and HbA1c was 16%, 20% and 20%, respectively. According to AROC analysis, the optimal cut-points for the diagnosis of diabetes were 6.4 mmol/L for FPG, 11.1 mmol/L for 2h PG, and 5.7% for HbA1c. At these cut-points the three measurements has identical sensitivity (87%) and similar specificity (87%-90%) for detecting type 2 diabetes. The AROC curve for detecting type 2 diabetes was not significantly different between any of the three measurements (FPG 0.96, 2h PG 0.90, and HbA1c 0.95).

The association of FPG, 2h PG and HbA1c with retinopathy and microalbuminuria was assessed by Tapp et al. (2006). Data were obtained from 2,182 participants with retinal photographs and 2,389 with urinary albumin/creatinine results from the AusDiab study (subjects aged ≥ 25 years). The prevalence of retinopathy in the first eight deciles of FPG and HbA1c and the first nine deciles of 2 h PG was 7.2, 6.6, and 6.3%, respectively, showing no variation with increasing glucose or HbA1c (subjects with known diabetes were excluded from these analyses). Above these levels, the prevalence of retinopathy rose sharply to 18.6, 21.3, and 10.9%, respectively. The thresholds for increased prevalence of retinopathy were ≥ 7.1 mmol/L for FPG, ≥ 6.1% for HbA1c, and ≥ 13.1 mmol/L for 2h PG. The prevalence of microalbuminuria rose more gradually across the deciles for each glycaemic measure. The thresholds were less clear than for retinopathy, but were found at ≥ 7.2 mmol/L for FPG and ≥ 6.1% for HbA1c, with no evidence of a threshold for 2h PG. For FPG the adjusted threshold for retinopathy using a change point model was 8.5 mmol/L (95%CI 6.4-10.6%, p =

4 0.008) and for HbA1c ≥ 6.0% (95% CI 3.9-7.0%, p = 0.064). The association of 2h PG and retinopathy was not assessed due to limited numbers, and there was no significant thresholds observed for any measure of glycaemia with microalbuminuria using change point models.

Ito and colleagues (2000a) evaluated FPG, 2h PG and HbA1c for the diagnosis of diabetes based on the prevalence of retinopathy. The subjects were 12,208 Japanese atomic-bomb survivors who underwent an OGTT between 1965 and 1997 (mean age at initial test 59 years). The prevalence of retinopathy increased sharply and significantly above the eighth decile with FPG ( ≥ 7.0 mmol/L), above the seventh decile for 2h PG ( ≥ 11.0 mmol/L) and above the ninth decile of HbA1c (≥ 7.3%).

Wong and colleagues (2008) assessed data from three cross-sectional studies to examine the relationship between FPG and retinopathy for the diagnosis of diabetes. The three cohorts included 3,162 Australian subjects aged 45-97 years from the Blue Mountains Eye Study (BMES), 2,182 Australian subjects aged 25-90 years from the Australian Diabetes, Obesity and Lifestyle Study (AusDiab) and 6,079 US subjects aged 45-84 years from the Multi-Ethnic Study of Atherosclerosis (MESA). The prevalence of retinopathy was 11.5% in BMES, 9.6% in AusDiab and 15.8% in MESA. Results indicate inconsistent evidence for a uniform glycaemic threshold for retinopathy, with the suggestion of a continuous relationship. Across the three cohorts, a FPG cut-point of ≥ 7.0 mmol/L had a low sensitivity ranging from 15-39% for detecting retinopathy, with specificity between 81-96%. The AROC for FPG in detecting retinopathy was low and ranged from 0.56 to 0.61. In a separate analysis, the relationship between 2h PG and prevalent retinopathy was assessed in the AusDiab cohort. A 2 hour plasma glucose cut-point of ≥ 11.1 mmol/L performed worse than FPG in identifying prevalent retinopathy in this population, with a sensitivity of 25%, specificity of 81% and AROC of 0.54. The authors also reported a continuous relationship between prevalent retinopathy and glycated haemoglobin in the MESA cohort, with change point models showing no evidence of a glycaemic threshold.

The DETECT-2 collaboration conducted an analysis to determine whether there is a glycaemic threshold for diabetic retinopathy (Colagiuri et al. Diabetes Care in press). Three glycaemic measures, FPG, 2h PG and HbA1c, were examined. The analysis included 12 studies from nine countries with a total of 47,364 participants aged 20-79 years with gradable retinal photographs. The prevalence of any retinopathy in people with known diabetes was 23.1%, newly diagnosed diabetes 5.4%, impaired glucose tolerance (IGT) 2.8%, impaired fasting glucose (IFG) 4.3% and normal glucose tolerance (NGT) 4.0%. Based on visual inspection of vigintile distribution, there was a glycaemic threshold for diabetes-specific retinopathy (moderate or more severe retinopathy), at 6.4-6.8 mmol/L for FPG, 9.8-10.6 mmol/L for 2h PG and 6.4-6.8% for HbA1c. When change point analyses with glycaemic measures plotted as the continuous variable were used, no threshold was found for any measure of glycaemia for diabetes-specific retinopathy. Based on ROC analyses, the optimal cut-points for detecting diabetes-specific retinopathy in all subjects were 6.5 mmol/L for FPG, 12.4 mmol/L for 2 h PG and 6.3% for HbA1c. At these cut-points the AROCs, sensitivities and specificities were 0.87, 82% and 81% for FPG; 0.89, 83% and 83% for 2h PG; and 0.90, 86% and 86% for HbA1c.

HbA1c and incident microvascular complications A recent study by Massin and colleagues (in press, Archives of Ophthalmology) compared the predictive values of baseline HbA1c and FPG for the development of retinopathy over 10 years in 700 French subjects (aged 30-65 years at entry) from the DESIR study. Of the study population, 235 had diabetes (treatment of FPG ≥ 7.0 mmol/L at least once over the preceding nine years), 238 always had NGT, and 227 had IFG at least once. The 44 subjects with retinopathy at 10 years had higher baseline mean HbA1c (6.4 ± 1.6% vs. 5.7 ± 0.7%) and FPG (7.2 ± 2.7 mmol/L vs. 5.9 ± 1.2 mmol/L) than those without retinopathy (both p < 0.0001). The 10-year prevalence of retinopathy was 3.6% in the entire population and 16% for those with HbA1c ≥ 6.5% and FPG ≥ 6.5 mmol/L. The 10-year prevalence of retinopathy was 3.3% for HbA1c < 6.0% and 6.8% for those with a higher HbA1c. An HbA1c of 6.0% had a positive predictive value (PPV) of 6.8%, a negative predictive value (NPV) of 97%, a sensitivity of 16%, a specificity of 97%, and a positive likelihood ratio (PLR) of 2.0 for 10-year retinopathy. For an HbA1c of 6.5%, these values were 15.9%, 97%, 7.9%, 97% and 2.4. For an FPG of 6.0 mmol/L these values were 8.6%, 97%, 27%, 90% and 2.6, while for a FPG of 6.5 mmol/L they were 17.4%, 97%, 21%, 96% and 5.7. A threshold above which retinopathy increased could not be determined from these results due the small sample size and low frequency of 10-year retinopathy.

Van Leiden and colleagues (2003) evaluated the effect of HbA1c, among other risk factors, on the incidence of retinopathy in 233 people aged 50-74 years with normal and abnormal glucose metabolism from the Hoorn Study. Average follow-up was 9.4 years (range 7.9-11.0 years). The cumulative incidences of retinopathy among those with normal, impaired, and diabetic glucose metabolism were 7.3%, 13.6%, and 17.5%, respectively. The cumulative incidence increased from 6.0% for those in the lowest tertile of HbA1c to 20.7% for those in the highest tertile (p = 0.005 for trend). The crude odds ratio for retinopathy were 2.01 and 2.71 for individuals with impaired glucose metabolism and those with type 2 diabetes, respectively, compared with individuals with normal glucose metabolism. The adjusted odds ratio for retinopathy was 3.29 (95%CI 1.11-9.72) for the highest tertile of HbA1c at baseline. Limiting this analysis to those without type 2 diabetes, the adjusted odds ratio for retinopathy in the highest tertile of baseline HbA1c was 3.54 (0.94-13.37). Baseline HbA1c was significantly higher in those who developed retinopathy at follow-up (6.1 ± 1.0%) compared with those who did not (5.6 ± 1.0%, p = 0.03).

Prospective data were also reported by the McCance et al. (1994) on the development to microvascular complications. However, as the data involved a combination of measurement of HbA1 and measurement of HbA1c, it was considered inappropriate for inclusion in this review.

6 Summary

1. The major objective of diagnosing diabetes is to prevent premature mortality and complication-related morbidity. Therefore it seems logical to consider diagnosis in terms of risk of complications.

2. Diagnostic criteria would ideally be derived from a study of outcomes and complications in an untreated prospective cohort measuring different potential diagnostic criteria at baseline. Alternatively outcomes could be compared with different diagnostic criteria in intervention studies. A sub-group analysis of the ADDITION study might have the power to examine this.

3. In the absence of the above information, the relationship of complications (diabetes-specific) with direct or indirect measures of glucose can be examined, either prospectively or in cross-sectional analysis.

4. Most of the data of the relationship of measures of glycaemia and retinopathy are derived from cross-sectional studies. HbA1c levels associated with retinopathy ranged from 5.8-7.3%. The DETECT-2 analysis pooled data from 47,364 people and reported an HbA1c of approximately 6.5% as the threshold for diabetes- specific retinopathy.

5. The DESIR study examined FPG and HbA1c and 10-year incident retinopathy. A threshold above which retinopathy increased could not be determined due to small sample and low frequency of 10-year retinopathy. An HbA1c of 6.5% had a PPV of 15.9%, NPV of 97%, sensitivity of 7.9%, and specificity of 97%.

Acknowledgements Funding for the systematic review was provided by the World Health Organization.

7 References

Colagiuri, S., C. M. Y. Lee, T. Y. Wong, B. Balkau, J. Shaw and K. Borch-Johnsen (In press, Diabetes Care). "Is there a glycemic threshold for diabetic retinopathy?". Engelgau, M. M., T. J. Thompson, W. H. Herman, J. P. Boyle, R. E. Aubert, S. J. Kenny, A. Badran, E. S. Sous and M. A. Ali (1997). "Comparison of fasting and 2-hour glucose and HbA1c levels for diagnosing diabetes. Diagnostic criteria and performance revisited." Diabetes Care 20 (5): 785-791. Ito, C., R. Maeda, S. Ishida, H. Harada, N. Inoue and H. Sasaki (2000a). "Importance of OGTT for diagnosing diabetes mellitus based on prevalence and incidence of retinopathy." Diabetes Res Clin Pract 49 (2-3): 181-186. Massin, P., C. Lange, J. Tichet, S. Vol, A. Erginay, M. Cailleau, E. Eschwege and B. Balkau (In press, Archives of Ophthalmology). "HbA1c and fasting plasma glucose as predictors of retinopathy at ten years: the French D.E.S.I.R. Study." McCance, D. R., R. L. Hanson, M. A. Charles, L. T. Jacobsson, D. J. Pettitt, P. H. Bennett and W. C. Knowler (1994). "Comparison of tests for glycated haemoglobin and fasting and two hour plasma glucose concentrations as diagnostic methods for diabetes." BMJ 308 (6940): 1323-1328. Miyazaki, M., M. Kubo, Y. Kiyohara, K. Okubo, H. Nakamura, K. Fujisawa, Y. Hata, S. Tokunaga, M. Iida, Y. Nose and T. Ishibashi (2004). "Comparison of diagnostic methods for diabetes mellitus based on prevalence of retinopathy in a Japanese population: the Hisayama Study." Diabetologia 47(8): 1411-1415. Schunemann, H. J., A. D. Oxman, J. Brozek, P. Glasziou, R. Jaeschke, G. E. Vist, J. W. Williams, Jr., R. Kunz, J. Craig, V. M. Montori, P. Bossuyt and G. H. Guyatt (2008). "Grading quality of evidence and strength of recommendations for diagnostic tests and strategies." BMJ 336 (7653): 1106-1110. Tapp, R. J., P. Z. Zimmet, C. A. Harper, M. P. de Courten, D. J. McCarty, B. Balkau, H. R. Taylor, T. A. Welborn and J. E. Shaw (2006). "Diagnostic thresholds for diabetes: the association of retinopathy and albuminuria with glycaemia." Diabetes Res Clin Pract 73 (3): 315-321. The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus (1997). "Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus." Diabetes Care 20 (7): 1183-1197. van Leiden, H. A., J. M. Dekker, A. C. Moll, G. Nijpels, R. J. Heine, L. M. Bouter, C. D. Stehouwer and B. C. Polak (2003). "Risk factors for incident retinopathy in a diabetic and nondiabetic population: the Hoorn study." Arch Ophthalmol 121 (2): 245-251. WHO (2006). Definition and diagnosis of diabetes mellitus and intermediate hyperglycemia . Geneva, World Health Organization. Wong, T. Y., G. Liew, R. J. Tapp, M. I. Schmidt, J. J. Wang, P. Mitchell, R. Klein, B. E. Klein, P. Zimmet and J. Shaw (2008). "Relation between fasting glucose and retinopathy for diagnosis of diabetes: three population-based cross- sectional studies." Lancet 371 (9614): 736-743.

8 Table 1 HbA1c and prevalent microvascular complications – study characteristics

Author, year Subject no Age Prevalence of Inclusion/ exclusion HbA1c test method Glucose Diabetes Blood and country and gender (years) diabetes (%) criteria method diagnostic sample (M/F) criteria Colagiuri et 47,364 20-79 14.3 Age 20-79 years with Varies by study Varies by WHO 1999 Varies by al. (in press, 22,127/ gradable retinal study study Diabetes Care), 25,237 photographs and data for at International least one measure of glycaemia (FPG, 2h PG or HbA1c) Engelgau et 1,018 Mean: 35.6 ≥ 20 years old, Egyptian Affinity chromatography Glucose WHO 1980 Capillary al. (1997), 417/601 45 (note: includes people with (Pierce Scientific) oxidase blood and Egypt known diabetes, many of CV: 6.0% Serum whom were receiving anti- glucose hyperglycaemic treatment) Expert 2,821 40-74 NR NR NR NR NR NR Committee NR (1997), US Ito et al. 12,208 58.6 ± NR Japanese atomic bomb HPLC Glucose WHO 1999 Venous (2000a), 6,440/5,768 11.6 survivors oxidase plasma Japan McCance et 960 ≥ 25 14-26 depending Pima Indian subjects ≥ 25 HPLC Potassium WHO 1985 Venous al. (1994), US 384/576 on measurement years of age not receiving ferricyanide plasma – Pima Indian and cut-point insulin or oral (26.3 for 2-h PG ≥ hypoglycaemic treatment at 11.1 mmol/L) baseline Miyazaki et 1,637 40-79 21-23 depending Age 40-79 years, not HPLC Glucose WHO 1999 Venous al. (2004), on measurement receiving insulin treatment oxidase plasma Japan (21 for 2-h PG ≥ (note: includes people 11.1 mmol/L) receiving oral antihyperglycaemic treatment) Tapp et al. 2,476 Mean: 34.5 Age ≥ 25 years Boronate affinity HPLC Olympus WHO 1999 Venous (2006), 1,114/1,362 59 (Bio-Rad Variant AU600 plasma Australia Haemoglobin Testing analyser System) CV: < 2% 2-h PG = 2 hour plasma glucose; ADA = American Diabetes Association; BMI = body mass index; CV = coefficient of variation; HPLC = high-performance liquid chromatography; NR = not reported; WHO = World Health Organization.

9 Table 2 HbA1c, FPG and 2-h PG cut-points associated with prevalent microvascular complications Study Complication HbA1c FPG 2-h PG Optimum AROC Sensitivity Specificity Optimum AROC Sensitivity Specificity Optimum AROC Sensitivity Specificity cut-point (%) (%) cut-point (%) (%) cut-point (%) (%) (%) (mmol/L) (mmol/L) Colagiuri et Retinopathy al. (ROC curve ≥6.3 0.90 86 86 ≥6.5 0.87 82 81 ≥12.4 0.89 83 83 (in press, analysis) Diabetes Care) Retinopathy (visual inspection 6.4-6.8 NR NR NR 6.4-6.8 NR NR NR 9.8-10.6 NR NR NR of decile distribution) Engelgau et Bi-modal: al. (1997) - Entire ≥6.7 NR 68 100 ≥7.2 NR 84 100 ≥11.5 NR 90 100 population Retinopathy#:

- Entire ≥7.6 0.82 NR NR ≥6.6 0.85* NR NR ≥14.4 0.86* NR NR population Expert Retinopathy Committee, ≥6.2 NR NR NR ≥6.7 NR NR NR ≥10.8 NR NR NR (1997) Ito et al. Retinopathy ≥7.3 NR NR NR ≥7.0 NR NR NR ≥11.0 NR NR NR (2000a) McCance et Retinopathy ≥7.0 NR 78 85 ≥7.2 NR 81 80 ≥13.0 NR 88 81 al. (1994) WHO equivalent ≥6.1 NR 81 77 ≥6.8 NR 81 77 ≥11.1 NR 88 76 ROC curve ≥5.7 0.95 87 90 ≥6.4 0.96 87 87 ≥11.1 0.90 87 90 analysis Miyazaki et Retinopathy ≥5.8 NR NR NR ≥6.5 NR NR NR ≥11.0 NR NR NR al. (2004) Tapp et al. Retinopathy ≥6.1 NR NR NR ≥7.1 NR NR NR ≥13.1 NR NR NR (2006) Microalbuminuria ≥6.1 NR NR NR ≥7.2 NR NR NR NR NR NR NR Retinopathy§ ≥6.0 NR NR NR ≥8.5 NR NR NR NR NR NR NR Microalbuminuria NIL - - - NIL - - - NR NR NR NR * Significantly different from HbA1c (p < 0.01); # Median decile value; § By change point analysis. 2-h PG = 2 hour plasma glucose; AROC = Area under the receiver operator characteristic curve; FPG = fasting plasma glucose; NR = Not reported; ROC = receiver operator characteristic; WHO = World Health Organization.

10 Table 3 HbA1c and incident microvascular complications – study characteristics

Author, Subject no Age Follow- Incidence of Inclusion/ exclusion criteria HbA1c test method Glucose Diabetes Blood year and and gender (years) up diabetes (%) method diagnostic sample country (M/F) (years) criteria Massin et al. 700 30-65 10 NR Aged 30-65 years. Excluded if HPLC (Hitachi/Merck- Glucose NR Venous (in press, 504/196 Retinopathy: uninterpretable retinal photographs VWR) or oxidase plasma Archives of 6.3 DCA 2000 automated Ophthalmol), immunoassay system France (Bayer Diagnostics) Van Leiden 233 50-74 9.4 NR Aged 50-74 years from Hoorn, HPLC (Modular Glucose WHO 1999 Venous et al. (2003), 124/109 Retinopathy: Netherlands. Diabetes Monitoring dehydrogenase plasma Netherlands 11.6 system; Bio-Rad) Normal range: 4.3-6.1% HPLC = high-performance liquid chromatography; NR = not reported; WHO = World Health Organization.

11 Table 4 HbA1c and FPG cut-points associated with incident diabetes complications

Study Complication HbA1c FPG Optimum AROC Sensitivity Specificity Optimum AROC Sensitivity Specificity cut-point (%) (%) cut-point (%) (%) (%) (mmol/L) Massin et al. (in press, Retinopathy ≥ 6.0 NR 16 97 ≥ 6.5 NR 21 96 Archives of Ophthalmol) AROC = Area under the receiver operator characteristic curve; FPG = fasting plasma glucose; NR = Not reported.

12 Table 5. Evidence table for HbA1c and prevalent microvascular complications

Author (year), Evidence Level of Evidence Magnitude of Relevance population Quality Rating Level Study Type effect rating Rating Colagiuri et al. (in press, Pooled Diabetes Care), N/A High High High Analysis International Engelgau et al. (1997), III-2 Cohort Medium High High Egypt Expert Committee III-2 Cohort Medium Medium High (1997), US Ito et al. (2000a), Japan II Cohort High High High McCance et al. (1994), II Cohort High High High US – Pima Indian Miyazaki et al. (2004), III-2 Cohort High High High Japan Tapp et al. (2006), III-2 Cohort High Medium High Australia

Table 6. Evidence table for HbA1c and incident microvascular complications

Author (year), Evidence Level of Evidence Magnitude of Relevance population Quality Rating Level Study Type effect rating Rating Massin et al. (in press, Prospective Archives of Ophthalmology ), II High Medium High Cohort France Van Leiden et al. (2003), Prospective II High Medium High Netherlands Cohort

13 Table 7. GRADE table for HbA1c and detection of prevalent microvascular complications

Factors that may decrease quality of evidence No. of Study Final Outcome Effect per 1000 1 Importance studies design quality Limitations Indirectness Inconsistency Imprecision Reporting bias

True positives 3 studies 2 Prev 80%: 672 ⊕⊕⊕O (patients with prevalent (31,797 Observational None 3 None None None Unlikely Prev 40%: 336 IMPORTANT moderate complications) patients) Prev 10%: 84

True negatives (patients 3 Prev 80%: 172 ⊕⊕⊕O without prevalent (31,797 Observational None 3 None None None Unlikely Prev 40%: 516 IMPORTANT moderate complications) patients) Prev 10%: 774

False positives (patients 3 Prev 80%: 28 incorrectly classified as 3 ⊕⊕⊕O (31,797 Observational None None None None Unlikely Prev 40%: 84 IMPORTANT having prevalent moderate patients) Prev 10%: 126 complications)

False negatives (patients 3 Prev 80%: 128 incorrectly classified as 3 ⊕⊕⊕O (31,797 Observational None None None None Unlikely Prev 40%: 64 IMPORTANT not having prevalent moderate patients) Prev 10%: 16 complications) 4 studies Inconclusive 4 (19,142 Observational – – – – – – – IMPORTANT patients) NOT Cost Not reported – – – – – – – – RELEVANT

1 Based on combined sensitivity of 84% and specificity of 86% 2 One study contained pooled data from 8 studies with 29,819 participants 3 Although not a serious limitation, one study oversampled people with known diabetes 4 These 4 studies did not report information on sensitivity and specificity of HbA1c for predicting prevalent microvascular complications 14 Table 8. GRADE table for HbA1c and incident microvascular complications

Factors that may decrease quality of evidence No. of Study Final Outcome Effect per 1000 2 Importance studies design quality Limitations Indirectness Inconsistency Imprecision Reporting bias

True positives Prev 80%: 128 1 study Not ⊕⊕OO (patients with incident Observational None None N/A 2 Unlikely Prev 40%: 64 IMPORTANT (700 patients) assessable 3 low complications) Prev 10%: 16

True negatives (patients Prev 80%: 194 1 Not ⊕⊕OO without incident Observational None None N/A 2 Unlikely Prev 40%: 582 IMPORTANT (700 patients) assessable 3 low complications) Prev 10%: 873

False positives (patients Prev 80%: 6 incorrectly classified as 1 2 Not ⊕⊕OO Observational None None N/A Unlikely Prev 40%: 18 IMPORTANT having incident (700 patients) assessable 3 low Prev 10%: 27 complications)

False negatives (patients Prev 80%: 672 incorrectly classified as 1 2 Not ⊕⊕OO Observational None None N/A Unlikely Prev 40%: 336 IMPORTANT not having incident (700 patients) assessable 3 low Prev 10%: 84 complications) 4 1 study Observational – – – – – – – IMPORTANT Inconclusive (233 patients) NOT Cost Not reported – – – – – – – – RELEVANT

2 Based on combined sensitivity of 16% and specificity of 97% 2 Imprecision could not be assessed as confidence intervals were not reported 3 Inconsistency is not applicable with data from only one study 4 This study did not report information on sensitivity and specificity of HbA1c for predicting incident microvascular complications 15 Appendix 1

Search for HbA1c in the diagnosis of diabetes (search covers both sections: incident and prevalent complications associated with HbA1c)

Search 1: Database: Ovid MEDLINE Search Strategy: ------1 Diabetes Mellitus, Type 2/ (62685) 2 (type 2 diabetes or type II diabetes).tw. (42266) 3 (non?insulin dependent diabetes or NIDDM).tw. (7555) 4 1 or 2 or 3 (75337) 5 Hemoglobin A, Glycosylated/ (16909) 6 hba1c.tw. (8615) 7 h?emoglobin A1c.tw. (3166) 8 Glyco?h?emoglobin.tw. (653) 9 Glycated h?emoglobin.tw. (2802) 10 Glycosylated h?emoglobin.tw. (5302) 11 5 or 6 or 7 or 8 or 9 or 10 (24975) 12 Diagnosis/ (15662) 13 Diagnostic Tests, Routine/ (5441) 14 diagnos$.tw. (1271525) 15 exp Diabetes Complications/ (87841) 16 complication$.tw. (456183) 17 retinopath$.tw. (23219) 18 12 or 13 or 14 or 15 or 16 or 17 (1733665) 19 4 and 11 and 18 (4191) 20 limit 19 to (humans and yr="1990 - 2010") (3973)

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Search 2 – Embase

No. Query Results #4 AND #12 AND #21 AND [humans]/lim AND [1990- #22 4132 2010]/py #13 OR #14 OR #15 OR #16 OR #17 OR #18 OR #19 OR #21 2677720 #20 #20 'retinopathy':ab,ti OR 'retinopathies':ab,ti 28677 #19 'complication':ab,ti OR 'complications':ab,ti 569736 #18 'diabetic retinopathy'/de 22102 'diagnosis':ab,ti OR 'diagnostic':ab,ti OR 'diagnosed':ab,ti OR #17 1545712 'diagnoses':ab,ti #16 'laboratory diagnosis'/de 35794 #15 'diagnostic procedure'/de 60017 #14 'diagnostic test'/de 46436 #13 'diagnosis'/de 805045 #12 #5 OR #6 OR #7 OR #8 OR #9 OR #10 OR #11 36114 #11 'glycosylated hemoglobin'/de 10917 'glycosylated haemoglobin':ab,ti OR 'glycosylated #10 6271 hemoglobin':ab,ti #9 'glycated haemoglobin':ab,ti OR 'glycated hemoglobin':ab,ti 3457 #8 'glycohaemoglobin':ab,ti OR 'glycohemoglobin':ab,ti 801 #7 'haemoglobin a1c':ab,ti OR 'hemoglobin a1c':ab,ti 2600 #6 hba1c:ab,ti 8781 #5 'hemoglobin a1c'/de 21712 #4 #1 OR #2 OR #3 103193 'non insulin dependent diabetes':ab,ti OR 'noninsulin #3 13423 dependent diabetes':ab,ti OR 'niddm':ab,ti #2 'type 2 diabetes':ab,ti OR 'type ii diabetes':ab,ti 55623 #1 'non insulin dependent diabetes mellitus'/de 87826

Search 3 – Pubmed

Search History

Search Queries Result

#18 Search #4 AND #10 AND #17 Limits: Humans, Publication Date from 1990 to 2010 7191

#17 Search #11 or #12 or #13 or #14 or #15 or #16 6064084

#16 Search retinopath*[Title/Abstract] 23768

#15 Search complication*[Title/Abstract] 474432

#14 Search diabetes complications[MeSH Terms] 86714

#13 Search diagnos*[Title/Abstract] 1320078

#12 Search diagnostic tests, routine[MeSH Terms] 5308

#11 Search diagnosis[MeSH Terms] 5190551

#10 Search #5 or #6 or #7 or #8 or #9 24308

#9 Search glycosylated haemoglobin or glycosylated hemoglobin[Title/Abstract] 18889

#8 Search glycated haemoglobin or glycated hemoglobin[Title/Abstract] 17668

#7 Search glycohaemoglobin or glycohemoglobin[Title/Abstract] 670

#6 Search hba1c[Title/Abstract] 9034

#5 Search hba1c[MeSH Terms] 16240

#4 Search #1 or #2 or #3 87454

#3 Search non?insulin dependent diabetes or niddm[Title/Abstract] 76711

#2 Search type 2 diabetes or type II diabetes[Title/Abstract] 75342

#1 Search type 2 diabetes[MeSH Terms] 60587

Search 4 – Cinahl

# Query Limiters/Expanders Results

Limiters - Published Date from: 19900101-20101231;

S20 S4 and S11 and S18 Human 512 Search modes - Boolean/Phrase

Search modes - S19 S4 and S11 and S18 703 Boolean/Phrase

Search modes - S18 S12 or S13 or S14 or S15 or S16 or S17 148780 Boolean/Phrase

Search modes - S17 TI retinopath* or AB retinopath* 1585 Boolean/Phrase

Search modes - S16 TI complication* or AB complication* 38685 Boolean/Phrase

Search modes - S15 TI diagnos* or AB diagnos* 109484 Boolean/Phrase

Search modes - S14 (MH "Diagnosis, Laboratory") 6119 Boolean/Phrase

Search modes - S13 (MH "Diagnostic Tests, Routine") 783 Boolean/Phrase

Search modes - S12 (MH "Diagnosis") 2056 Boolean/Phrase

Search modes - S11 S5 or S6 or S7 or S8 or S9 or S10 5717 Boolean/Phrase

TI ( glycosylated haemoglobin or glycosylated hemoglobin ) or Search modes - S10 837 AB ( glycosylated haemoglobin or glycosylated hemoglobin ) Boolean/Phrase

TI ( glycated haemoglobin or glycated hemoglobin ) or AB ( Search modes - S9 390 glycated haemoglobin or glycated hemoglobin ) Boolean/Phrase

TI ( glycohaemoglobin or glycohemoglobin ) or AB ( Search modes - S8 66 glycohaemoglobin or glycohemoglobin ) Boolean/Phrase

TI ( (haemoglobin a1c or hemoglobin a1c) ) or AB ( Search modes - S7 816 (haemoglobin a1c or hemoglobin a1c) ) Boolean/Phrase

Search modes - S6 TI hba1c or AB hba1c 2208 Boolean/Phrase

Search modes - S5 (MH "Hemoglobin A, Glycosylated") 3908 Boolean/Phrase

Search modes - S4 S1 or S2 or S3 18051 Boolean/Phrase

TI ( (non insulin dependent diabetes or noninsulin dependent diabetes or non-insulin dependent diabetes or niddm) ) or AB ( Search modes - S3 839 (non insulin dependent diabetes or noninsulin dependent Boolean/Phrase diabetes or non-insulin dependent diabetes or niddm) )

TI ( (type 2 diabetes or type II diabetes) ) or AB ( (type 2 Search modes - S2 10448 diabetes or type II diabetes) ) Boolean/Phrase

Search modes - S1 (MH "Diabetes Mellitus, Non-Insulin-Dependent") 15554 Boolean/Phrase

Search 5 – Psycinfo

Database: PsycINFO Search Strategy: ------1 (type 2 diabetes or type II diabetes).tw. (2117) 2 (non?insulin dependent diabetes or NIDDM).tw. (148) 3 1 or 2 (2248) 4 hba1c.tw. (493) 5 h?emoglobin A1c.tw. (199) 6 Glyco?h?emoglobin.tw. (19) 7 Glycated h?emoglobin.tw. (102) 8 Glycosylated h?emoglobin.tw. (311) 9 4 or 5 or 6 or 7 or 8 (883) 10 diagnosis/ (24273) 11 diagnos$.tw. (177767) 12 "Complications (Disorders)"/ (756) 13 complication$.tw. (11553) 14 retinopath$.tw. (379) 15 10 or 11 or 12 or 13 or 14 (189699) 16 3 and 9 and 15 (106) 17 limit 16 to (human and yr="1990 - 2010") (104)

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Search 6 – Cochrane Library

Current Search ID Search Hits #1 MeSH descriptor Diabetes Mellitus, Type 2 explode all trees 6415 #2 (type 2 diabetes or type II diabetes):ti,ab,kw 8982 (non insulin dependent diabetes or non insulin dependent diabetes or non-insulin dependent diabetes #3 2020 or niddm):ti,ab,kw #4 (#1 OR #2 OR #3) 9548 #5 MeSH descriptor Hemoglobin A, Glycosylated , this term only 2656 #6 (hba1c):ti,ab,kw 1642 #7 (haemoglobin a1c or hemoglobin a1c):ti,ab,kw 788 #8 (glycohaemoglobin or glycohemoglobin):ti,ab,kw 69 #9 (glycated haemoglobin or glycated hemoglobin):ti,ab,kw 476 #10 (glycosylated haemoglobin or glycosylated hemoglobin):ti,ab,kw 3168 #11 (#5 OR #6 OR #7 OR #8 OR #9 OR #10) 4352 #12 MeSH descriptor Diagnosis , this term only 65 #13 MeSH descriptor Diagnostic Tests, Routine , this term only 293 #14 (diagnos*):ti,ab,kw 66662 #15 MeSH descriptor Diabetes Complications explode all trees 3896 #16 (complication*):ti,ab,kw 71382 #17 (retinopath*):ti,ab,kw 1861 #18 (#12 OR #13 OR #14 OR #15 OR #16 OR #17) 129125 #19 (#4 AND #11 AND #18), from 1990 to 2010 1141

Appendix 2

NHMRC Evidence Hierarchy: designations of ‘levels of evidence’ according to type of research question (NHMRC 2007)

Level Intervention Diagnostic accuracy Prognosis Aetiology Screening Intervention I A systematic review of level II A systematic review of level A systematic review of level A systematic review of level A systematic review of level II Studies II studies II studies II studies studies II A randomised controlled trial A study of test accuracy A prospective cohort study A prospective cohort study A randomised controlled trial with: an independent, blinded comparison with a valid reference standard, among consecutive persons with a defined clinical presentation III-1 A pseudorandomised controlled trial A study of test accuracy All or none All or none A pseudorandomised (i.e. alternate allocation or some with: an independent, controlled trial other method) blinded comparison with a (i.e. alternate allocation or

valid reference standard, some other method) among non-consecutive persons with a defined clinical presentation II-2 A comparative study with A comparison with reference Analysis of prognostic A retrospective cohort study A comparative study with concurrent controls: standard that does not meet factors amongst persons in concurrent controls: ▪ Non-randomised, the criteria required for a single arm of a ▪ Non-randomised, experimental trial Level II and III-1 evidence randomised controlled trial experimental trial ▪ Cohort study ▪ Cohort study ▪ Case-control study ▪ Case-control study ▪ Interrupted time series with a control group III-3 A comparative study without Diagnostic case-control A retrospective cohort study A case-control study A comparative study without concurrent controls: study concurrent controls: ▪ Historical control study ▪ Historical control study ▪ Two or more single arm ▪ Two or more single arm study study ▪ Interrupted time series without a parallel control group IV Case series with either post-test Study of diagnostic Case series, or cohort study of A cross-sectional study or Case series or pre-test/post-test outcomes yield (no reference persons at different stages of case series standard) disease (Source: NHMRC 2007) 23

Study Assessment Criteria

I. Study quality criteria

Systematic reviews 1. Were the questions and methods clearly stated? 2. Is the search procedure sufficiently rigorous to identify all relevant studies? 3. Does the review include all the potential benefits and harms of the intervention? 4. Does the review only include randomised controlled trials? 5. Was the methodological quality of primary studies assessed? 6. Are the data summarised to give a point estimate of effect and confidence intervals? 7. Were differences in individual study results adequately explained? 8. Is there an examination of which study population characteristics (disease subtypes, age/sex groups) determine the magnitude of effect of the intervention? 9. Were the reviewers' conclusions supported by data cited? 10. Were sources of heterogeneity explored?

Randomised controlled trials 1. Were the setting and study subjects clearly described? 2. Is the method of allocation to intervention and control groups/sites independent of the decision to enter the individual or group in the study ? 3. Was allocation to study groups adequately concealed from subjects, investigators and recruiters including blind assessment of outcome? 4. Are outcomes measured in a standard, valid and reliable way? 5. Are outcomes measured in the same way for both intervention and control groups? 6. Were all clinically relevant outcomes reported? 7. Are factors other than the intervention e.g. confounding factors, comparable between intervention and control groups and if not comparable, are they adjusted for in the analysis? 8. Were >80% of subjects who entered the study accounted for at its conclusion?% 9. Is the analysis by intention to intervene (treat)? 10. Were both statistical and clinical significance considered? 11. Are results homogeneous between sites? (Multi-centre/multi-site studies only).

Cohort studies 1. Are study participants well-defined in terms of time, place and person? 2. What percentage (%) of individuals or clusters refused to participate? 3. Are outcomes measured in a standard, valid and reliable way? 4. Are outcomes measured in the same way for both intervention and control groups? 5. Was outcome assessment blind to exposure status? 6. Are confounding factors, comparable between the groups and if not comparable, are they adjusted for in the analysis? 7. Were >80% of subjects entered accounted for in results and clinical status described?

8. Was follow-up long enough for the outcome to occur 9. Was follow-up complete and were there exclusions from the analysis? 10. Are results homogeneous between sites? (Multicentre/multisite studies only).

Case-control studies 1. Was the definition of cases adequate? 2. Were the controls randomly selected from the source of population of the cases? 3. Were the non-response rates and reasons for non-response the same in both groups? 4. Is possible that over-matching has occurred in that cases and controls were matched on factors related to exposure? 5. Was ascertainment of exposure to the factor of interest blinded to case/control status? 6. Is exposure to the factor of interest measured in the same way for both case and control groups in a standard, valid and reliable way (avoidance of recall bias)? 7. Are outcomes measured in a standard, valid and reliable way for both case and control groups? 8. Are the two groups comparable on demographic characteristics and important potential confounders? and if not comparable, are they adjusted for in the analysis? 9. Were all selected subjects included in the analysis? 10. Was the appropriate statistical analysis used (matched or unmatched)? 11. Are results homogeneous between sites? (Multicentre/multisite studies only).

Diagnostic accuracy studies 1. Has selection bias been minimised 2. Were patients selected consecutively? 3. Was follow-up for final outcomes adequate? 4. Is the decision to perform the reference standard independent of the test results (ie avoidance of verification bias)? 5. If not, what per cent were not verified? 6. Has measurement bias been minimised? 7. Was there a valid reference standard? 8. Are the test and reference standards measured independently (ie blind to each other) 9. Are tests measured independently of other clinical and test information? 10. If tests are being compared, have they been assessed independently (blind to each other) in the same patients or done in randomly allocated patients? 11. Has confounding been avoided? 12. If the reference standard is a later event that the test aims to predict, is any intervention decision blind to the test result? (Sources: adapted from NHMRC1999, NHMRC 2000a, NHMRC 2000b, Liddle et al 96; Khan et al 2001)

Study quality – Rating The following was used to rate the quality of each study against the study type criteria listed above.

High: all or all but one of the criteria were met

Medium: 2 or 3 of the criteria were not met

Low: 4 or more of the criteria were not met

II. Classifying magnitude of the effect

Ranking Statistical significance Clinical importance of benefit High Difference is statistically AND There is a clinically significant important benefit for the full range of estimates defined by the confidence interval. Medium Difference is statistically AND The point estimate of effect significant is clinically important BUT the confidence interval includes some clinically unimportant effects

Low Difference is statistically AND The confidence interval significant| does not include any clinically important effects OR Difference is not statistically AND The range of estimates significant (no effect) or defined by the confidence shows a harmful effect interval includes clinically important effects. (Source: adapted from the NHMRC classification (NHMRC 2000b)

III. Classifying the relevance of the evidence

Ranking Relevance of the evidence

High Evidence of an effect on patient-relevant clinical outcomes, including benefits and harms, and quality of life and survival Or Evidence of an effect on a surrogate outcome that has been shown to be predictive of patient-relevant outcomes for the same intervention

Medium Evidence of an effect on proven surrogate outcomes but for a different intervention Or Evidence of an effect on proven surrogate outcomes but for a different intervention and population

Low Evidence confined to unproven surrogate outcomes.

(Source: adapted from the NHMRC classification (NHMRC 2000b)