Iga/Igg-Deamidated Gliadin Peptide) for Celiac Disease

1238 Article

see related editorial on page x Offce-Based Point of Care Testing (IgA/IgG-Deamidated Gliadin Peptide) for Celiac Disease

Michelle S. Lau, MBChB1, Peter D. Mooney, MD1, William L. White, MBChB1, Michael A. Rees, BMedSci1, Simon H. Wong, MBChB1, Marios Hadjivassiliou, FRCP2, Peter H. R. Green, MD3, Benjamin Lebwohl, MD3 and David S. Sanders, FRCP1

Objectives: Celiac disease (CD) is common yet under-detected. A point of care test (POCT) may improve CD detection. We aimed to assess the diagnostic performance of an IgA/IgG-deamidated gliadin peptide (DGP)-based POCT for CD detection, patient acceptability, and inter-observer variability of the POCT results.

COLON/SMALL BOWEL Methods: From 2013–2017, we prospectively recruited patients referred to secondary care with gastrointestinal symptoms, anemia and/or weight loss (group 1); and patients with self-reported gluten sensitivity with unknown CD status (group 2). All patients had concurrent POCT, IgA-tissue transglutaminase (IgA-TTG), IgA-endomysial antibodies (IgA-EMA), total IgA levels, and duodenal biopsies. Five hundred patients completed acceptability questionnaires, and inter-observer variability of the POCT results was compared among fve clinical staff for 400 cases.

Results: Group 1: 1000 patients, 58.5% female, age 16–91, median age 57. Forty-one patients (4.1%) were diagnosed with CD. The sensitivities of the POCT, IgA-TTG, and IgA-EMA were 82.9, 78.1, and 70.7%; the specifcities were 85.4, 96.3, and 99.8%. Group 2: 61 patients, 83% female; age 17–73, median age 35. The POCT had 100% sensitivity and negative predictive value in detecting CD in group 2. Most patients preferred the POCT to venepuncture (90.4% vs. 2.8%). There was good inter-observer agreement on the POCT results with a Fleiss Kappa coeffcient of 0.895.

Conclusions: The POCT had comparable sensitivities to serology, and correctly identifed all CD cases in a gluten sensitive cohort. However, its low specifcity may increase unnecessary investigations. Despite its advantage of convenience and rapid results, it may not add signifcant value to case fnding in an offce-based setting.

Am J Gastroenterol (2018) 113:1238–1246. https://doi.org/10.1038/s41395-018-0143-3

Introduction NCGS using a double blind placebo controlled challenge [15], self- Celiac disease (CD) is a systemic autoimmune disease associated reported gluten sensitivity describes individuals who complain of with gastrointestinal and extra-gastrointestinal symptoms, trig- gastrointestinal and/or non gastrointestinal symptoms triggered by gered by gluten in genetically susceptible individuals [1]. It afects gluten ingestion and present to physicians accordingly. Exclusion 0.3–2.4% of the general population globally [2–9]. CD afects one of CD and wheat allergy is fundamental in this group of patients. It in 100 in the United Kingdom, but only 24% are detected [10]. is essential to distinguish NCGS from CD, as patients with NCGS Similar observations are also apparent in Europe [3], the United do not seem to be at risk of the complications seen in CD, although States [11], and worldwide [12]. Tis is partly because symptoms they derive symptomatic beneft from a gluten free diet [16]. More- of CD can be non-specifc and difcult for clinicians to recog- over, any delays in celiac testing before individuals embark on a nize. Tis is further compounded by an emerging clinical entity, self-imposed gluten free diet could cause diagnostic challenges. non-celiac gluten sensitivity (NCGS), which is clinically indistin- Early diagnosis of CD is important for the improvement of guishable from CD [13, 14]. Although the Salerno criteria defne patients’ quality of life and the prevention of complications such

1Academic Department of Gastroenterology, Royal Hallamshire Hospital, Sheffeld Teaching Hospitals, Sheffeld, UK. 2Academic Department of Neurosciences and University of Sheffeld, Royal Hallamshire Hospital, Sheffeld Teaching Hospitals, Sheffeld, UK. 3Celiac Disease Centre, Columbia University Medical Centre, New York, NY, USA. Correspondence: M.S.L. (email: [email protected]) Received 26 January 2018; accepted 4 May 2018; Published online 19 June 2018

The American Journal of Gastroenterology Volume 113 | August 2018 www.nature.com/ajg by international guidelines [24, fndingcase for CDinat risk individuals recommended has been © 2018The AmericanCollegeof Gastroenterology with duodenal biopsies patients. was inall performed (IgA-EMA) and DGP-based the POCT, Simtomax. An endoscopy A (IgA) levels, IgA-TTG antibodies, IgA-endomysial antibodies studyin the were concurrently tested with total immunoglobulin tive of patients practice. clinical All consented who to participate accurate assessment of sensitivities the that of is POCT refec the - study as to so avoid referral bias, thus tertiary providing amore by careserology primary their physicians were excluded from the CD were excluded. Patients were who referred with positive celiac or dyspepsia),anemia and/or weight loss. Patients with known with gastrointestinal symptoms (abdominal pain, diarrhea and/ ation. patients were who referred to gastroenterology for- evalu further UK, from March 2013–January 2017. We prospectively recruited Te study took place at Royal the Hallamshire Hospital, Shefeld, Study designandpatients Methods asymptomatic patients at present [13, atic reported review insufcient to support evidence screening for through fnding case [18, detection [17].Similar results were obtained by other groups risk symptomswith high inaclinic setting 3.3–4.7%CD yielded cies. We have previously shown that testing serological inpatients as osteoporosis, hip fractures, and lymphoproliferative malignan- interpretation. ability of POCT, the and inter-observer the variability of test result sensitivity. aims were secondary Our to evaluate patient accept - toms, anemia and/or weight loss, andself-report gluten who those patients presenting care to with secondary gastrointestinal symp- IgA/IgG-DGP-basedthe POCT, Simtomax, CDin indetecting with sensitivities of 72.2, 77.8,and 94.4%,respectively [28]. thatrevealed Simtomax signifcantly outperformed other the two, and Simtomax (IgA/IgG-deamidated (DGP)) peptide gliadin comparingtrial Biocard (IgA-TTG), Quick Test Celiac (IgA-TTG), compared to conventional serology. Arecent to head POCTs head widespread use, probably clinical due to inferior their sensitivities glutaminase (IgA-TTG). However, POCTs these have not entered past within the decade, majority the IgA-tissue detecting trans- forneed duodenal biopsies. POCTs Several have developed been results could provide immediate guidance for physician the on the inandetection, particularly consultation, ofce-based where the and rapid celiac antibody results may have arole inimproving case fnger prick point of care that test provides (POCT) convenience a lack of awareness of guidelines, the inconvenience and cost. A inadequate. Tisdue could be to amultitude of factors, including suggests that current fnding case strategies may with serology be prior performed had serology to endoscopy their [26, utilized, where only 30%of patients CDor with suspected anemia viduals, it shown has been that testing serological for CD is under Group one consisted of patients presenting care to secondary Our primary aim was to assess the diagnostic accuracy of aim was primary toOur assess diagnostic accuracy the Despite guidelines recommending celiac testing in at risk indi- ]. On the other19]. Onthe hand, arecent system- 25]. 20– 23]. For reasons, these ]. Tis 27]. Tis - the POCT,the and duodenal biopsies were patients. inall taken concurrently tested with total IgA levels, IgA-TTG, IgA-EMA, and prior to endoscopy their guidelines as [29, per asked a6-week to gluten undertake challenge of 10 CD were excluded. with Tose reduced or no gluten intake were celiac status of patients these was unknown. Patients with known extra-gastrointestinal symptoms related to gluten ingestion. Te with self-reported gluten sensitivity, with gastrointestinal and/or 1 for Fig. functioning test. illustration See of POCT. the ence of IgA. Athird inbuilt red control band ensured acorrectly IgG-DGP positivity. Asecond single red band indicated pres the - results were indicated by presence the of red a solid band for IgA/ bufer solution. Te result was available afer 10 followeddevice, by application the of fve drops of provided the prick technique. sample Te blood was applied then to test the of venous capillary was obtained blood through asimple fnger gold antihuman antibodies detector. as asignal Asample of 25 onis lateral based fow immunochromatography using colloidal IgA/IgG-DGP antibodies, as well as presence the of IgA. Te assay Augurix Diagnostics, Rheinfelden, Switzerland. It both detects Te for DGP-based POCT CD, Simtomax, was manufactured by Point ofcaretest family and history response to agluten diet.Non-celiac free causes and or other DQ8, supporting DQ2 (HLA) information such as normal gluten containing diet, positive human antigen leukocyte and/orTTG EMA)with Marsh 3villous atrophy. Te defnition of on CDwas positive (positive based serology Defnitions ofdiagnoses department.pathology Standard 3 processed, orientated, and inparafn embedded waxby the in formalin at of time the gastroscopy. the Specimens were then from of second the part duodenum. the biopsy Each was fxed biopsy from duodenal bulb the and four quadrantic biopsies with asingle bite pass technique, per including at least one In total, at least fve biopsies were from taken duodenum the Histological evaluation and therefore not tested. was not serology Sussex, available UK).DGP inour laboratory ured BN2 on nephelometer aBehring (Haywards Heath, West (Bindingsections Site, Birmingham, UK). Total IgA was meas- byEMA was detected immunofuorescence on primate esophagus (ELISA) kits (Aesku Diagnostics, Wendelsheim, Germany). IgA- IgA-TTG was assayed using enzyme-linked immunosorbent assay Celiac serology biopsy samples. recorded on most was the from based severedetected grade the ing Marsh to modifed the criteria [31].Te histological grade or results. serology POCT Villous atrophy accord was graded - by gastrointestinal histopathologists without knowledge of the levels were stained with hematoxylin and and eosin, reported Group two consisted of patients presenting care to secondary Seronegative on CDwasMarsh based 3villous atrophy on a Point ofcare Test (igA/igG-DGP)forceliacDisease The American Journal American μ m thick sections atm thicksections three of Gastroenterology ]. All patients30]. All were minutes. Positive g gluten/day μl 1239 COLON/SMALL BOWEL 1240 lau et al.

Fig. 1 three possible outcomes of the point of care test results. Red band A indicates a positive result, red band B indicates the presence of IgA, red band CT is the control line, indicating a correctly functioning test. Left: a solid red band A indicating a positive test; Middle: an absence of a red band A indicating a negative test; Right: a faint pink band A which was classifed as a negative test, as none of the patients with a faint band A had celiac disease in our

COLON/SMALL BOWEL cohort

of seronegative villous atrophy were extensively investigated for, Inter-observer variability of the POCT results including giardiasis, tuberculosis, whipple’s disease, small bowel Inter-observer variability of the POCT results was assessed bacterial overgrowth, helicobacter pylori, human immunodef- in 400 consecutive patients in group one. Each observer ciency virus, autoimmune enteropathy and drug related causes. recorded whether there was a defnite red band, a faint red Marsh 3 villous atrophy secondary to CD was the reference stand- band, or an absence of a red band. Tere were fve observ- ard used in our study for the diagnostic performance evaluation of ers in total for each case, consisting of one gastroenterologist the POCT and serology. and four other randomly selected allied health care profes- Potential CD was defned as positive serology with no villous sionals (for example, nurses). All observers were trained to atrophy (Marsh 0–2), with supporting information such as positive recognize positive, negative, and indeterminate results. Obser- HLA DQ2 or DQ8 and family history. vation of the results was carried out indoors under fuorescent Non-celiac gluten sensitivity was diagnosed in patients self- lighting. reporting symptoms related to gluten who had negative serology, absence of villous atrophy, and symptom response to a gluten free Ethical considerations diet and gluten challenge. A 6-week gluten challenge of 10 g glu- Te study protocol was approved by the Yorkshire and the ten/day was proposed for group two patients entering the study Humber Research Ethics committee and registered with the who had reduced or absent gluten intake prior to their investiga- local research and development department of Shefeld tions. Teaching Hospital NHS Foundation Trust under the registra- tion number STH15416. Written consent was obtained from all Patient acceptability of the POCT patients. Tere are no validated patient acceptability questionnaires in the literature for POCTs. Terefore, we devised a questionnaire Statistical analysis consisting of fve questions regarding the acceptability of the Data were summarized by descriptive statistics, including counts POCT (comfort level, convenience, and satisfaction with result and percentages for categorical data, and medians and ranges for availability) which was flled in by 500 consecutive patients afer continuous parameters. Te diagnostic accuracies of the POCT, having had the POCT performed. Tey were asked to rate on IgA-TTG, and IgA-EMA were presented with sensitivity, speci- a Likert scale of one to fve for each question, with one being a fcity, positive (PPV), and negative predictive values (NPV). negative experience and fve being a positive experience. Tese Clopper–Pearson method was used to calculate the confdence 500 patients all had previous experience of a venepuncture. Tey intervals for the sensitivities. Inter-observer variability was pre- were also asked to state their preferred mode of testing: POCT, sented using Fleiss Kappa coefcient, where 0 indicates no agree- venepuncture, or no preference. A similar acceptability question- ment and 1 indicates perfect agreement. Cohen’s efect size (r) naire for venepuncture was completed by a separate cohort of 63 for patient acceptability between the POCT and venepuncture patients afer having had a venepuncture to act as controls. Tese groups was measured using Mann–Whitney U test, where r = 0.1, questionnaires were given out to both groups to fll in indepen- 0.3, and 0.5 indicates small, medium, and large efect size, respec- dently and anonymously, and the questionnaires were collected by tively. Statistical analysis was performed using IBM SPSS statistics a member of staf on completion. version 24.

The American Journal of Gastroenterology Volume 113 | August 2018 www.nature.com/ajg © 2018The AmericanCollegeof Gastroenterology on gluten aself-imposed diet underwent free agluten challenge: 16 group two of our study. Twenty-three patients were who previously from study. the Atotal of 61patients consuming gluten entered a 6-week gluten challenge prior to investigations were excluded patients were who on gluten aself-imposed dietand free declined demonstrated2. inFig. for aforementioned the curves (ROC) tic tests for group one are are displayed inTables performance of POCT, the IgA-TTG, and IgA-EMA for group one IgA-TTG and IgA-EMA (85.9 vs. 96.3 vs. 99.8%). Te diagnostic vs. 70.7%).However, its specifcity was signifcantly lower than was comparablePOCT to IgA-TTG and IgA-EMA (82.9vs.78.1 atrophy confned to duodenal bulb the only. Te sensitivity of the patients (9/41 of total the celiac cohort), and three had apositive all POCT. Nine Tree IgA defcient patients were with CD (3/45 diagnosed in 29patients ingroups one and two combined (29/1061 bydetected total IgA levels from laboratory the assay was found Forty-one patients (4.1%)were with CD. diagnosed IgA defciency were 585/1000females (58.5%);age range 16–91,median age 57. consented for participation entered group one of study. the Tere one are illustrated inTable Patient demographics and presenting characteristics ingroup Results detecting celiacdiseaseinsymptomaticpatients(groupone;n Table 2 characteristics table Table 1 Female Male Diarrhea Abdominal pain Weight loss Anemia Dyspepsia Accuracy %(95% CI) Negative likelihoodratio(95%CI) Positive likelihoodratio(95%CI) Negative predictivevalue%(95%CI ) Positive predictivevalue%(95%CI) Specifcity %(95%CI) Sensitivity %(95%CI) In group two, 70patients self-reported gluten sensitivity. Nine The diagnosticaccuracyofthepointcaretest,IgA-tissuetransglutaminase antibodiesandIgA-endomysialin Group onepatientdemographicsandpresenting = 22%) had ultra-short CD with Marsh 3villous No. ofpatients 585/1000 (58.5%) 415/1000 (41.5%) 75/1000 (7.5%) 159/1000 (15.9%) 104/1000 (10.4%) 194/1000 (19.4%) 549/1000 (54.9%) and 3.Receiver operating2 and characteris- 1. One thousand eligible patients who 85.3 (83.0–87.4) 0.2 (0.1–0.4) 5.7 (4.6–7.0) 99.2 (98.4–99.6) 19.5 (16.5–23.0) 85.4 (83.0–87.6) 82.9 (67.9–92.9) Point ofcaretest Celiac diseaseyield 27/585 (4.6%) 14/415 (3.4%) 8/75 (10.7%) 13/159 (8.2%) 6/104 (5.8%) 9/194 (4.6%) 8/549 (1.5%) = 2.7%). = 6.7% = 1000, celiacdiseaseprevalence4.1%) for group two are displayed inTables diagnostic performance of POCT, the IgA-TTG, and IgA-EMA 91.8%, 97.77%for IgA-TTG and IgA-EMA, respectively). Te 100% (vs. sensitivity 88.2%, 94.1% and negative predictive value demonstratedPOCT asensitivity and negative predictive value of 17/61 (27.9%)with CD, and 2/61(3.3%)with potential CD. Te aforementioned tests for group two are demonstrated3 inFig. Forty-two patients (42/61 mind, ataxia, lethargy, foggy sia, tongue tingling, and arthralgia). predominantly neurological complaints (e.g., headache, paresthe- toms, and ten patients reported extra-gastrointestinal symptoms, ers. Te vast majority (57/61)of patients had gastrointestinal symp- patients were tested positive for EMAby general their practition- 51/61 females (82.9%);age range 17–73,median age 35.Eighteen at toued doso least until investigations the took place. Tere were 38 patients were consuming agluten containing dietand contin- copy were due performed to signifcant symptoms. Te remaining 4 weeks of gluten challenge at point which and serology endos the - patients managed a6-week challenge and could only seven tolerate size diference two the groups between was large (r cant of acceptability the aspects inall questionnaire, and efect the ence scores inthe two the groups between were statistically- signif patienthigher satisfaction compared to venepuncture. Te difer Te level of agreement dropped for faint red bands (Kappa 0.781), red bands (Kappa 0.887)and absence of red bands (Kappa 0.956). overall. Sub-analysis level of ahigh revealed agreement for defnite resultPOCT interpretation, with a Fleiss Kappa coefcient of 0.895 groups for of tests. the eachaspect Table 95.5 (94.0–96.7) 0.2 (0.1–0.4) 20.8 (14.5–30.0) 99.0 (98.3–99.5) 47.1 (38.3–56.0) 96.3 (94.8–97.4) 78.1 (62.4–89.4) IgA-tissue transglutaminaseantibodies results bythereferencestandard Table 3 POCT + POCT − In regards to patient acceptability, had signifcantly POCT the Tere degree of was agood inter-observer agreement on the 6 shows median the scores and statistical diferences in both Group 1:crosstabulationofthepointcaretest(POCT) CD 34 7 Point ofcare Test (igA/igG-DGP)forceliacDisease CD Not 140 819 The TTG + TTG − American Journal American =

68.9%) were with NCGS, diagnosed CD 32 9 4 and 5 and CD Not 36 923 98.6 (97.7–99.2) 0.3 (0.2–0.5) 339.2 (83.8–1373.2) 98.8 (98.0–99.2) 93.6 (78.2–98.3) 99.8 (99.3–100.0) 70.7 (54.5–83.9) IgA-endomysial antibodies of Gastroenterology . ROC curves for the curves . ROC EMA + EMA −

= 0.506–0.656). 0.506–0.656). CD 29 12 CD Not 2 957 . - 1241 COLON/SMALL BOWEL 1242 lau et al.

where there were 31 such cases within the 400 assessed. None of positive antibodies (either POCT or serology) were biopsied [32– these 31 patients had CD. Only solid red bands were classifed as a 37]. Additionally, some POCT studies measured the sensitivities positive test for the purpose of diagnostic calculations in our study, against serology rather than duodenal histology as the reference and faint red bands were interpreted as negative. Figure. 1 illus- standard [35, 38, 39]. Tese limitations could lead to a positive trates the three possible outcomes of the POCTs results. ascertainment bias, thereby falsely elevating the reported sensitivities. Another strength of this study is that our patient cohort had Discussion a CD prevalence consistent with real life case fnding in patients To our knowledge, this is the largest study to date evaluating the diagnostic accuracy of the DGP-based POCT, Simtomax. Tis is also the frst study to explore the practicalities of this POCT Table 5 Group 2: cross tabulation of the point of care test (POCT) including patient acceptability and inter-observer variability of results by the reference standard test result interpretation. CD Not CD Not CD Not One of the strengths of this study is that all participants had CD CD CD duodenal biopsies taken, irrespective of their celiac antibodies POCT + 17 9 TTG + 15 3 EMA + 16 1 or POCT results. Tis ensured that no false negative cases of CD POCT 0 35 TTG 2 41 EMA 1 43 would be missed. Tis methodology contributed to a major dif- − − − COLON/SMALL BOWEL ference to most POCT studies for CD, where only patients with

ROC curve ROC curve 1.0 Source of the 1.0 Source of the curve curve POCT POCT EMA EMA 0.8 TTG 0.8 TTG Reference line Reference line

0.6 0.6 Sensitivity 0.4 Sensitivity 0.4

0.2 0.2

0.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.60.8 1.0 1 - Specificity 1 - Specificity Fig. 2 Group 1 receiver operating characteristic (ROC) curve for the point Fig. 3 Group 2 receiver operating characteristic (ROC) curve for the point of care test (POCT), IgA-endomysial antibodies (EMA), and IgA-tissue of care test (POCT), IgA-endomysial antibodies (EMA) and IgA-tissue transglutaminase antibodies (TTG). Area under the curve (AUC) for transglutaminase antibodies (TTG). Area under the curve (AUC) for each each test were 0.842 (CI: 0.77-0.9), 0.853 (CI: 0.77-0.94), and 0.871 test were 0.898 (CI: 0.82–0.98), 0.959 (CI: 0.89–1.0) and 0.907 (CI: (CI: 0.8-0.95), respectively. CI = confdence interval 0.81–1.0) respectively. CI = confdence interval

Table 4 The diagnostic accuracy of the point of care test, IgA-tissue transglutaminase antibodies, and IgA-endomysial antibodies in detecting celiac disease in patients who self-reported gluten sensitivity (group two; n = 61, celiac disease prevalence 27.9%)

Point of care test IgA-tissue transglutaminase antibodies IgA-endomysial antibodies

Sensitivity % (95% CI) 100 (80.5–100) 88.2 (63.6–98.5) 94.1 (71.3–99.9) Specifcity % (95% CI) 79.6 (64.7–90.2) 93.2 (81.3–98.6) 97.7 (88.0–99.9) Positive predictive value % (95% CI) 65.4 (51.3–77.2) 83.3 (62.3–93.8) 94.1 (69.6–99.1) Negative predictive value % (95% CI) 100 91.8 (81.0–97.3) 97.7 (86.5–99.6) Positive likelihood ratio (95% CI) 4.9 (2.7–8.8) 12.9 (4.3–39.1) 41.4 (5.9–288.5) Negative likelihood ratio (95% CI) 0 0.1 (0–0.5) 0.06 (0.01–0.4) Accuracy % (95% CI) 85.3 (73.8–93.0) 91.8 (81.9–97.3) 96.7 (88.7–99.6)

The American Journal of Gastroenterology Volume 113 | August 2018 www.nature.com/ajg did not biopsy controls (i.e., duodenal biopsies take inseronegative fawsmethodological in most studies [42].Firstly, many studies indicated that fgures these were likely due falsely high to to be and were specifcities > and IgA-EMA from published data were 93%(range 70–100%) atic in2006showed review sensitivities that pooled the of IgA-TTG 43]. Tere are potential several reasons for Although this. asystem- and IgA-EMATTG compared to previous studiesserological [42, outcomewas asecondary and not main the of focus study. this resentation of patient acceptability. However, patient acceptability ability. Qualitative would interviews give a more informative rep- provided aquantitative rather than qualitative measure of accept- naires literature, inthe of scale using and aLikert methodology the acceptability questionnaire as there were no validated question- of patient acceptability of POCT. the We our own devised POCT assays were not performed. Another limitation is evaluation the Kingdom (UK)and is not available inour center. Terefore, DGP is not serology laboratory widely available DGP United inthe and lateralogy) fow immunochromatography However, (POCT). detection by sensitivitiesthe laboratory DGP between assay (serol - comparison wouldof as auseful serology laboratory act DGP of real practice. accurate refection of diagnostic performance the of tests these in andacteristics pre-test probability of group one allowed amore generalizabilityrestricts the of fndings. their Te patient char in previous studies [34, POCT © 2018The AmericanCollegeof Gastroenterology [ risk symptoms,with high havewhich reported 3–4.7% to been be from 1to5,withbeinganegativeexperienceand5positive Table 6 17,

Quality ofcare Convenience

Blood collectionprocess No preference Prefers venepuncture Prefers pointofcaretest Preference What is noteworthy is generally the lower sensitivities of IgA- Tere are a few limitations to our study. Ideally, measurement the within thesameconsultation(forPOCT)vsatalaterdatevenepuncture) Satisfaction scoreforobtaininganddiscussingthetestresultswithclinician days toaweek(forserologyviavenepuncture) Satisfaction scoreforobtainingtestresultswithin10 POCT) vsseparatelyfromtheconsultationbyphlebotomyservice Satisfaction scoreforhavingthetestperformedduringconsultation(for Score forspeedandeaseofthetest Score forcomfortlevelofthetest 18]. Amuch CDprevalence higher is acommon limitation Patient acceptabilityforthepointofcaretest(POCT)andconventionalvenepuncture.AcceptabilitywasscoredwithaLikertscale 98% (range 90–100%) for authors the both, 40, ]. Tis tertiary referral bias 41]. Tis tertiary minutes (forPOCT)vsafew - assessed the diagnostic outcomes the assessed of cohort, this with sample sizes gluten sensitivity, there are four studies literature inthe which comparison to other studies. patientsall including controls and CDprevalence the low being in appeared lower to be than average inour study, where we biopsied huge variability of IgA-TTG sensitivities and why sensitivities the and 82.6–100%,respectively factors these explain [48].All the variable sensitivities and ranging specifcities, from 71.1–95.5% of three diferent trial head found kits serological also TTG widely for Marsh [47 ]. Arecent to using head curve 3histology aROC ple was above or below IgA-TTG defned the level cut of point agreement poor still among laboratories as sam to the - whether same the even when IgA-TTG ELISAassay kit there was used, was UK, giving diferent IgA-TTG titers. Arecent study showed that Furthermore, over 30diferent IgA-TTG assay kits are inthe used unitsbody and reference ranges are arbitrary and method-specifc. to lead diferentcould also IgA-TTG sensitivities. IgA-TTG anti- Lastly, lack the of standardization of IgA-TTG laboratory assays sensitivityincreased the and positive predictive value of IgA-TTG. at high 74% forvery studies. both Tis again could have falsely demonstratedbeen previously [46], since CD prevalence the was may not have refected performance their inreal practice, as it has ofSecond results the all, from aforementioned the two studies still cifcities of IgA-TTG 78.3–95% and to be 97.5–98.4% respectively. twoIn studies these fact, demonstrated sensitivities the and- spe cluded that only two out of 11studies biopsied controls [44, of IgA-TTGnostic accuracy and IgA-DGP authors [43],the con- sensitivities of serology. In asubsequent meta-analysis of diag the - patients), creating positive ascertainment bias enhanced which the In regards to prevalence the of CD inindividuals self-report who 4.8 4.8 4.8 4.7 4.7 34/500 (6.8%) 14/500 (2.8%) 452/500 (90.4%) No. ofpatients Point ofcaretest(POCT) Point ofcare Test (igA/igG-DGP)forceliacDisease The American Journal American 2.9 3.1 2.9 3.3 3.3 Venepuncture of Gastroenterology U p U p U p U p U p Mann–Whitney Utest < 0.001, < 0.001, < 0.001, < 0.001, < 0.001, = 988.0, = 583.5, = 1086.5, = 2182.5, = 2988.5, r r r r r Z Z = 0.64 = 0.656 = 0.617 = 0.566 = 0.506 Z Z Z = 15.223, = 15.597, = 14.675, = 13.443, = 12.027, ]. 45]. 1243 COLON/SMALL BOWEL 1244 lau et al.

ranging from 93 to 238, and the prevalence of CD varying between respectively). With the 100% negative predictive value, the POCT 2 and 42.4% [49–52]. In our study, the CD prevalence of 27.9% could potentially save USD $5141 per 100 endoscopies through within the self-reported gluten sensitivity cohort lies within the duodenal biopsy avoidance (vs. routine duodenal biopsy for ane- range of the reported data. Te wide variation in the reported dis- mia) in iron defcient patients with a negative POCT when used in ease prevalence is likely due to diferences in the study population, the pre-endoscopy setting, unless the patient has other high-risk study design, recruitment methods, and diagnostic criteria. For malabsorptive symptoms such as weight loss and diarrhea [27]. example, our disease prevalence of 27.9% is higher than the 7% Te advantages of the POCT over conventional serology are reported by Aziz et al. which derived from a UK population-based favorable patient acceptability and rapidly available results within questionnaire targeting individuals with gluten related symptoms 10 minutes. Nevertheless, despite there being no signifcant dif- [51], as opposed to symptomatic individuals actively presenting ference in the overall diagnostic performance between the POCT to primary care who were then referred on to secondary care for and serology based on ROC curve analysis, one must consider the further evaluation. Our group 2 patients’ gluten-related symptoms clinical impact of the high false positive rates of the POCT. Te may have prompted more proactive celiac screening by their gen- potential burden of a considerable increase in unnecessary inves- eral practitioners, thus possibly explaining the higher prevalence tigations may outweigh the benefts of a sensitive and convenient of seropositive patients (18/61), giving a higher disease prevalence. test. We have previously demonstrated that this POCT could be Nevertheless, afer excluding the 18 patients who were referred useful in CD monitoring, as it had a signifcantly higher sensitivity with positive EMA in group 2, the sensitivity and negative predic- than IgA-TTG in predicting persistent villous atrophy in known COLON/SMALL BOWEL tive value of the POCT remained at 100%, where all four cases of CD patients on a gluten-free diet (67.1% vs. 47.1%, p = 0.0005) CD were correctly identifed. [56]. Although the sensitivity of the POCT was still suboptimal, it POCTs for other laboratory measurements, such as human represented a stepwise improvement in current disease monitor- immunodefciency virus and international normalized ratio have ing compared to conventional serology. However, as a case fnd- been widely adopted in UK practice in both primary and second- ing tool in an ofce-based setting where the CD prevalence would ary care settings, owing to their clinical efectiveness and good be expected to be ~4%, as was in our study and other case fnd- patient acceptability [53, 54]. We have shown that this POCT had ing studies based on symptomatic cohorts [17], the POCT may a favorable acceptability to patients compared to venepuncture, not provide signifcant added value compared to conventional with 90.4% patients preferring the POCT. Most patients generally serology due to its low specifcity, albeit its similar sensitivity to found the POCT to be a simple and quick test to perform (it took IgA-TTG. on average 1 min to perform the test, and 10 min for the results to become available), and less painful than venepuncture. Table 6 illustrates the satisfaction scores for diferent aspects of the POCT Conclusion versus venepuncture. Te DGP-based POCT had comparable sensitivities to IgA-TTG With regards to the diagnostic performance of the POCT, the and IgA-EMA in detecting CD in symptomatic patients, and cor- sensitivity was comparable to IgA-TTG and IgA-EMA (82.9% rectly distinguished all cases of CD in a gluten sensitive cohort that vs. 78.1% vs. 70.7%). In our group one cohort, 7.3% (3/41) of the was consuming gluten. It also has the advantage of convenience, newly diagnosed patients had seronegative CD detected by the rapid result availability, and good patient acceptability. However, POCT alone whilst IgA-TTG was negative. An increase in diag- the POCT is limited by its low specifcity which may increase the nostic yield with DGP was also demonstrated by Hoerter et al. number of unnecessary investigations. Te POCT therefore may recently, where the use of IgA-DGP serology resulted in a 15% not add signifcant value when used for case fnding in a general increase in CD detection where IgA-TTG was negative [55]. How- ofce-based consultation compared to conventional serology. ever, the specifcity and PPV of the POCT were inferior to IgA- TTG and IgA-EMA (specifcities 85.4% vs. 96.3% vs. 99.8% and Conflict of interest PPVs 19.5% vs. 47.1% vs. 93.6%, respectively), due to a higher rate Guarantor of the article: David Sanders, MBChB, MD, of false positives. Tis could potentially lead to unnecessary fur- FACG, FRCP. ther investigations. A possible explanation of the low specifcity Specifc author contributions: MSL is involved in data collection, is that approximately half of the group one cohort had dyspepsia, analysis and interpretation of the data, statistical analysis, and which constituted low risk for CD, and hence may have lowered drafing of the manuscript; PDM is involved in data collection, the pre-test probability of CD and hence the positive predictive and analysis and interpretation of the data; WLW, MAR, SHW value. On the other hand, when the POCT was used in higher are responsible for data collection; MH, PHRG, BL are involved risk groups, such as patients who self-reported gluten sensitivity in analysis and interpretation of the data, and revision of the (group two), the positive predictive value increased to 65.4%, with manuscript; DSS is responsible for study concept and design, a 100% sensitivity and negative predictive value in detecting CD. analysis interpretation of the data, revision of the manuscript and Similarly, we have previously shown that the POCT had better study supervision. All authors have approved the manuscript. diagnostic performance when used in 133 patients with iron def- Financial support: None. ciency who were referred for an endoscopy (sensitivity, specifcity, Potential competing interests: DSS has received educational positive, and negative predictive value of 100, 82.2, 57.8, and 100%, research grants from Dr Schaer (a gluten-free food manufacturer)

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