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EDUCATION PRACTICE

GUIDELINES Early identification and management of chronic kidney disease in adults: summary of updated NICE guidance Serena Carville,1 David Wonderling,1 Paul Stevens,2 on behalf of the Guideline Development Group

1National Clinical Guideline Centre, The publication of an internationally accepted definition other abnormalities caused by tubular disorders, abnor- Royal College of Physicians, London and classification of chronic kidney disease (CKD) 12 years malities detected by histology, structural abnormalities NW1 4LE, UK ago precipitated a proliferation of research and literature detected by imaging, and previous kidney transplanta- 2East Kent Hospitals University NHS Foundation Trust, Canterbury surrounding the identification of CKD, risk factors for pro- tion. Cystatin C is an alternative endogenous filtration CT1 3NG, UK gression, and important prognostic factors.1 It also stimu- marker that can be used to estimate glomerular filtration Correspondence to: P Stevens lated continuing debate concerning the criteria used for rate. In people with GFR above 45 mL/min/1.73 m2, GFR [email protected] definition of CKD and exactly how ageing influences CKD estimates based on cystatin C are more powerful predic- Cite this as: BMJ 2014;349:g4507 2 3 doi: 10.1136/bmj.g4507 and its sequelae. The National Institute for Health and tors of clinical outcomes than is creatinine based esti- Care Excellence (NICE) has modified its previous recommen- mated GFR, especially in people with no proteinuria.7 8 This is one of a series of BMJ dations on the classification of CKD,4 partly based on Kidney • Do not diagnose CKD in people with: summaries of new guidelines 5 based on the best available Disease Improving Global Outcomes (KDIGO) and driven ––An estimated GFRcreatinine of 45-59 mL/min/ 2 evidence; they highlight important by prognostic data from large observational studies. NICE 1.73 m and recommendations for clinical has also recognised a requirement for better identification of ––An estimated GFRcystatinC of more than practice, especially where 2 uncertainty or controversy exists. people at risk of adverse outcome and covers some key areas 60 mL/min/1.73 m and Further information about the relating to the management of CKD, including frequency of ––No other marker of kidney disease. (New guidance and the supporting monitoring, progression of CKD, acute kidney injury, and recommendation.) evidence statements are in the full renin-angiotensin system blockade. This article summarises • To detect and identify proteinuria, use urine version on thebmj.com the most recent recommendations from NICE.6 :creatinine ratio in preference to :creatinine ratio, because it has greater Recommendations sensitivity for low levels of proteinuria. For NICE recommendations are based on systematic reviews of quantification and monitoring of high levels of thebmj.com best available evidence and explicit consideration of cost proteinuria (albumin:creatinine ratio ≥70 mg/mmol), Previous articles in this effectiveness. When minimal evidence is available, rec- protein:creatinine ratio can be used as an alternative. series ommendations are based on the Guideline Development Albumin:creatinine ratio is the recommended Group’s experience and opinion of what constitutes good method for people with diabetes. (Updated ЖЖLipid modification practice. Evidence levels for the recommendations are in recommendation.) and cardiovascular the full version of this article on thebmj.com. • Offer testing for CKD using estimated GFRcreatinine risk assessment and albumin:creatinine ratio to people with any of for the primary and Investigations for chronic kidney disease the following risk factors: secondary prevention of • Clinical laboratories should: ––Diabetes cardiovascular disease: ––Use the Chronic Kidney Disease ––Hypertension summary of updated Collaboration (CKD-EPI) creatinine equation to ––Acute kidney injury NICE guidance estimate GFRcreatinine, using creatinine assays ––Cardiovascular disease (ischaemic heart disease, (BMJ 2014;349:g4356) with calibration traceable to standardised reference chronic heart failure, peripheral vascular disease, ЖЖThe management material or cerebral vascular disease) of atrial fibrillation: ––Use creatinine assays that are specific (for example, ––Structural renal tract disease, renal calculi, or summary of updated enzymatic assays) and zero biased compared with prostatic hypertrophy NICE guidance isotope dilution mass spectrometry and ––Multisystem diseases with potential kidney (BMJ 2014;348:g3655) ––Participate in a UK national external quality involvement—for example, systemic ЖЖPrevention and assessment scheme for creatinine. (New erythematosus management of pressure recommendation.) ––Family history of end stage kidney disease (GFR Consider using eGFRcystatinC at initial diagnosis to category G5) or hereditary kidney disease ulcers: summary of NICE • confirm or rule out CKD in people with: ––Opportunistic detection of haematuria. (Updated guidance ––An estimated GFRcreatinine of 45-59 mL/min/ recommendation.) (BMJ 2014;348:g2592) 1.73 m2, sustained for at least 90 days and ЖЖManagement ––No proteinuria (albumin:creatinine ratio <3 mg/ Classification of chronic kidney disease of psychosis and mmol) or other marker of kidney disease. (New • Classify CKD by using a combination of GFR and schizophrenia in adults recommendation.) albumin:creatinine ratio (ACR) categories (as (BMJ 2014;348:g1173) Markers of kidney disease include albuminuria illustrated in figure 1). Be aware that: ЖЖEarly management of (albumin:creatinine ratio >3 mg/mmol), urine sediment ––Increased albumin:creatinine ratio is associated head injury: summary of abnormalities (haematuria, red blood cell casts, white with increased risk of adverse outcomes updated NICE guidance blood cell casts, oval fat bodies or fatty casts, granular ––Decreased GFR is associated with increased risk of (BMJ 2014;348:g104) casts, and renal tubular epithelial cells), electrolyte and adverse outcomes

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––Increased albumin:creatinine ratio and decreased Indications for referral GFR in combination multiply the risk of adverse • People with CKD in the following groups should outcomes. (New recommendation.) normally be referred for specialist assessment: An incidental finding of clinically important proteinu- ––GFR less than 30 mL/min/1.73 m2 (GFR category ria should always be considered in the context of GFR G4 or G5), with or without diabetes* category.­ ––Albumin:creatinine ratio 70 mg/mmol or more, unless known to be caused by diabetes and already Indications for renal ultrasound appropriately treated • Offer a renal ultrasound scan to all people with CKD who: ––Albumin:creatinine ratio 30 mg/mmol (category ––Have accelerated progression of CKD (see A3) or more, together with haematuria “Defining progression of CKD”) ––Sustained decrease in GFR of 25% or more and ––Have visible or persistent invisible haematuria a change in GFR category or sustained decrease ––Have symptoms of urinary tract obstruction in GFR of 15 mL/min/1.73 m2 or more within ––Have a family history of polycystic kidney disease 12 months and are aged over 20 years ––Hypertension that remains poorly controlled ––Have a GFR of less than 30 mL/min/1.73 m2 (GFR despite the use of at least four antihypertensive category G4 or G5) drugs at therapeutic doses (see also NICE clinical ––Are considered by a nephrologist to require a renal guideline 127 on hypertension (www.nice.org.uk/ biopsy. (Updated recommendation.) Guidance/CG127)) ––Known or suspected rare or genetic causes of CKD Frequency of monitoring ––Suspected renal artery stenosis. (Updated • Use figure 2 to guide the frequency of GFR monitoring recommendation.) for people with or at risk of CKD, but tailor it to the *Where this is a stable isolated finding, formal referral may not be person according to: indicated and advice may be all that is required. The aim is to avoid The underlying cause of CKD late referral of those people likely to progress to requirement for renal –– replacement therapy within one year. ––Past patterns of estimated GFR and albumin:creatinine ratio (but be aware that • People with CKD and renal outflow obstruction progression of CKD is often non-linear) should normally be referred to urological services, ––Comorbidities, especially heart failure unless urgent medical intervention is required—for ––Changes to their treatment (such as renin- example, for the treatment of hyperkalaemia, severe angiotensin-aldosterone system antagonists, non- uraemia, acidosis, or fluid overload. steroidal anti-inflammatory drugs, and diuretics) ––Intercurrent illness Pharmacotherapy ––Whether they have chosen conservative Choice of antihypertensive agent and blood pressure control management of CKD. (New recommendation.) • Offer a low cost renin-angiotensin system antagonist • Monitor people for the development or progression of to people with CKD and: CKD for at least two to three years after acute kidney ––Diabetes and an albumin:creatinine ratio of injury, even if serum creatinine has returned to 3 mg/mmol or more (category A2 or A3) baseline. (New recommendation.) ––Hypertension and an albumin:creatinine ratio of 30 mg/mmol or more (category A3) Defining progression of CKD ––An albumin:creatinine ratio of 70 mg/mmol • Define accelerated progression of CKD as: or more (irrespective of hypertension or ––A sustained decrease in GFR of 25% or more and a cardiovascular disease). (New recommendation.) change in GFR category within 12 months or The evidence to support these criteria is limited in ––A sustained decrease in GFR of 15 mL/min/1.73 people aged over 70 years. m2 per year. (New recommendation.) • Do not offer a combination of renin-angiotensin system antagonists to people with CKD. (New Self management recommendation.) • Ensure that systems are in place to: • Follow the treatment recommendations in NICE ––Inform people with CKD of their diagnosis clinical guideline 127 (www.nice.org.uk/Guidance/ ––Enable people with CKD to share in decision CG127) (on hypertension) for people with CKD, making about their care hypertension, and an albumin:creatinine ratio of less ––Support self management (this includes providing than 30 mg/mmol (categories A1 and A2) if they do information about blood pressure, smoking not have diabetes. (New recommendation.) cessation, exercise, diet, and medicines) and Blood pressure control recommendations for people enable people to make informed choices. (New with CKD and diabetes and an albumin:creatinine ratio recommendation.) of greater than 3 mg/mmol (categories A2 and A3) and People should be encouraged to take exercise, achieve hypertension were not updated. a healthy weight, stop smoking, and restrict salt intake • In people with CKD, aim to keep the systolic blood to less than 6 g/day according to existing guidance (see pressure below 140 mm Hg (target range 120-139 mm www.nice.org.uk/guidance/PH25). Hg) and the diastolic blood pressure below 90 mm Hg.

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Albumin:creatinine ratio (ACR) categories Oral antiplatelets and anticoagulants Glomerular ltration rate (mg/mmol), description and range • Offer antiplatelet drugs to people with CKD for the and albumin:creatinine ratio < - > secondary prevention of cardiovascular disease, categories and risk Normal to mildly Moderately Severely of adverse outcomes increased ACR increased ACR increased ACR but be aware of the increased risk of bleeding. (New A A A recommendation.) ≥ G Normal and high GFR No chronic Overcoming barriers - G kidney disease The use of thresholds for diagnosis of CKD and the defi- Mild reduction in GFR in the absence related to normal of markers of nition of progression remain contentious areas. In the range for a kidney damage whole adult population, the CKD-EPI creatinine equation young adult reduces bias in GFR estimation, affords greater precision, - Ga* Mild-moderate and is better at categorising people at higher risk of all

), description and range reduction in GFR cause mortality, cardiovascular mortality, myocardial  - Gb infarction, progression of CKD, and end stage kidney Moderate-severe 9 10 reduction in GFR Increasing risk of adverse outcomes disease. Categorisation by GFR in the new classifi- - G cation is complemented by categorisation of urinary Severe reduction in GFR albumin:creatinine ratio. Strong evidence shows that Glomerular ltration rate (GFR) categories (mL/min/. m < G both lower GFR and greater albumin:creatinine ratio are Kidney failure independently related to mortality, cardiovascular events, progression to end stage kidney disease, and also acute Increasing risk of adverse outcomes Low risk of adverse outcomes (if no other markers of kidney disease, no chronic kidney disease) kidney injury. This is important, although intervention Moderately increased risk trials in the different albumin:creatinine ratio categories High risk are lacking, albuminuria increases the risk of acute kid- Very high risk ney injury, and acute kidney injury predicts progression of CKD. The diagnosis of CKD in people without significant Fig 1 | Classification of chronic kidney disease by using glomerular filtration rate (GFR) and 2 albumin:creatinine ratio categories. *Consider using estimated GFRcystatinC for people with proteinuria in the GFR category 45-59 mL/min/1.73 m CKD G3aA1. Adapted with permission from reference 5 (G3aA1), especially older people, continues to raise con- cerns regarding over-diagnosis. Use of cystatin C identifies those at higher risk of adverse outcomes, including end stage kidney disease, and overcomes some of the concerns Albumin:creatinine ratio (ACR) categories Frequency of monitoring (mg/mmol), description and range relating to potential over-diagnosis and disease labelling. (number of times per year) < -€ >€ Another contentious area is the definition of progression by glomerular ltration rate Normal to mildly Moderately Severely and albumin:creatinine ratio of CKD. The recommendation is supported by more recent increased ACR increased ACR increased ACR category evidence and attempts to recognise both the inherent vari- A A A ability of serum creatinine in the assessment of GFR and ≥­€ G ≤ ≥ Normal and high GFR the fact that progression of kidney disease is often not 11‑13 ‘€-’­ G linear. We used the term “accelerated progression” in Mild reduction in GFR the knowledge that reported decline in GFR among people related to normal ≤ ≥ range for a with CKD may be lower (reviewed extensively in reference young adult 5). Finally, categorisation by GFR and albumin:creatinine -­ Ga ratio also provides a template for frequency of monitoring Mild-moderate  in people with established CKD and aids decision making ), description and range reduction in GFR Increasing risk of progression  €- Gb regarding referral. Moderate-severe ≤  ≥ reduction in GFR Contributors: All authors contributed to the conception and drafting of this article and to revising it critically. They have all approved this version. PS is -­ G  the guarantor. Severe reduction in GFR Glomerular ltration rate (GFR) categories (mL/min/.‹ m < G Competing interests: We have read and understood BMJ policy on ≥ Kidney failure declaration of interests and declare the following interests: SC is a member of the Kidney Disease Improving Global Outcomes (KDIGO) Methods Committee (no reimbursement is received); SC and DW are employees of Increasing risk of progression the Royal College of Physicians, National Clinical Guideline Centre, which is commissioned by NICE to develop clinical guidelines; PS is a co-investigator Fig 2 | Frequency of monitoring of glomerular filtration rate for people with or at risk of chronic kidney on an NIHR funded research project in progress, which is a multicentre disease. Albumin:creatinine ratio is an important indicator of cardiovascular risk and progression. study examining the accuracy of glomerular filtration rate estimation using Intensity of shading reflects risk of progression. Adapted with permission from reference 5 creatinine and cystatin C and albuminuria for monitoring disease; he has given lectures on guidelines, chronic kidney disease, and measurement of kidney function for the International Society of Nephrology, American Society of Nephrology, German Society of Nephrology, Renal Association, British • In people with CKD and diabetes, and also in Renal Society, US National Kidney Foundation, and Japanese Society of people with an albumin:creatinine ratio of 70 Nephrology (all professional societies in kidney disease; no reimbursement was received). The authors’ statements can be viewed at www.bmj.com/ mg/mmol or more (category A3), aim to keep the content/bmj/349/bmj.g4507/related#datasupp. systolic blood pressure below 130 mm Hg (target Provenance and peer review: Commissioned; not externally peer reviewed. range 120-129 mm Hg) and the diastolic blood pressure below 80 mm Hg. References are in the version on thebmj.com.

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RATIONAL TESTING Diagnosis of immediate food Cathal Steele,1 Niall Conlon,2 1 J David Edgar1 2

1Belfast Trust Regional A 10 month old girl with a history of eczema was brought to Box 1 | Key questions in an allergy focused history Service, Royal Hospitals, Belfast the emergency department with urticaria and BT12 6BA, UK without respiratory or circulatory features to suggest ana- Was there an exposure to a suspected ? 2Centre for Infection and Immunity, phylaxis (see glossary). Ten minutes before the symptoms The most common in children are , , and Queen’s University Belfast, Belfast, . In adults, peanut, tree , , and shellfish are most UK appeared she had eaten some lightly cooked (scrambled) common Correspondence to: C Steele egg. The emergency department doctor administered oral [email protected] How soon after exposure did symptoms begin? and instituted close clinical monitoring. Cite this as: BMJ 2014;349:g3695 Symptoms typically begin within minutes of exposure but can doi: 10.1136/bmj.g3695 Within 30 minutes symptoms had resolved, and the child take up to two hours was discharged after a six hour period of observation. The What were the reported symptoms and were they suggestive This series of occasional articles doctor explained the likely diagnosis of an egg allergy provides an update on the best of an allergic reaction? use of key diagnostic tests in the and recommended avoidance of foods containing egg. An Symptoms of an allergic reaction include immediate oral initial investigation of common or appointment with the GP to consider further investiga- pruritus and swelling, urticaria, abdominal pain, vomiting, important clinical presentations. tion or onward referral to a paediatric allergy service was throat tightness, stridor, cough, respiratory distress, The series advisers are Steve drowsiness, and collapse Atkin, professor of medicine, advised. When consulting their GP the next day, the par- Weill Cornell Medical College in ents asked about tests to confirm egg allergy and whether Were there additional cofactors present? Qatar, and Eric Kilpatrick, honorary an adrenaline auto-injector was necessary. Some allergic reactions need the addition of cofactors before professor, department of clinical the reaction is clinically apparent. Specific examples include biochemistry, Hull Royal Infirmary, infection, alcohol, exercise, and use of non-steroidal anti- Hull York Medical School. To What is the next investigation? inflammatory drugs (NSAIDs) suggest a topic for this series, Before allergy testing is carried out a focused history is essen- please email us at practice@bmj. tial (box 1). Urticaria and angioedema (see glossary) are com- Has there been uneventful exposure to the potential allergen com. before or after the reaction? patible with an immediate reaction to food Ask about how the food was prepared (raw versus cooked), but can also occur spontaneously without any allergic trigger. and consider a dose dependent threshold for reactivity. In immediate (IgE mediated) the allergen expo- Consider whether the implicated food has been correctly sure should have a close temporal relation with the onset of identified 1 symptoms. Symptoms will typically begin within seconds/ Is a non-allergic explanation possible? minutes of exposure to the allergen and resolve before 12 Did urticaria and angioedema persist despite avoidance hours. In this case, symptoms began within 10 minutes and of the reputed allergen? Has the same allergen been eaten the total duration of symptoms was two hours. since without adverse outcome? Spontaneous urticaria and The next appropriate investigation is to validate the clini- angioedema should be considered in these circumstances cal suspicion of egg allergy by performing skin prick or spe- cific IgE testing. Access to these tests for generalists can vary In our scenario, the GP measured specific IgE to between services and, in some instances, will first require both and egg , the results of which were referral to specialist allergy services. Though both methods 7.52 kU/L and 0.19 kU/L, respectively (reference range 0-0.35 of testing were assessed by the National Institute for Care kU/L), and did not request a “food panel” to five common food and Health Excellence (NICE) in the 2011 guideline for the allergens offered by the local laboratory. Panel testing detects diagnosis and assessment of food allergy in children,2 many specific IgE to several of the most commonly implicated aller- of the studies reviewed were of poor quality. The guideline gens. This screening approach is problematic and can give rise recommends these tests in the appropriate setting and when to unexpected positive results that can be difficult to interpret. there is adequate competency in the interpretation of results. For many non-specialists this interpretation can require the Specific IgE testing: limitations and difficulties in interpretation advice of experienced allergy practitioners. Detectable specific IgE does not necessarily imply an allergy.1 Patients can be sensitised, meaning that they have KEY POINTS raised serum concentrations of specific IgE to an allergen without associated immediate symptoms when exposed. Before you consider allergy testing, take a focused history: ask about the suspected allergen, The higher the specific IgE, the more likely it is that the test symptoms, and their timing in relation to suspected allergen exposure result will be clinically relevant. Despite this, the level of Skin prick and specific IgE testing should be used to diagnose immediate food allergy only when the clinical history supports this specific IgE does not predict the severity of symptoms. Cal- Select only the specific allergens suspected in the clinical history. The use of specific IgE food culation of specific IgE concentrations with 95% positive panels or a blanket screening approach is likely to yield positive results that are difficult to predictive values (table 1) has been used to improve diag- 1 interpret nostic accuracy. These values are typically calculated from Positive results of specific IgE or skin prick testing without clinical reactivity denote sensitisation patients with confirmed food allergy and, if used rationally and dietary restriction is not recommended (guided by the history), can lead to an improved certainty Unnecessary dietary restriction increases the risk of nutritional deficiencies and parental/ of the clinical diagnosis. In the case above the specific IgE patient anxiety results suggest a greater than 95% certainty that the diag- nosis of egg allergy considered before the tests is correct.

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ing in measurement and interpretation of results is required. thebmj.com Table 1 | Specific IgE concentrations with 95% positive Previous articles in this predictive values in children and infants*1 In some cases, such as with fruit and vegetables, skin prick series Allergen At mean age 5 In infants aged <2 testing with fresh allergen is desirable as the performance ЖЖInvestigating Egg 7 kUA/L 2 kUA/L of the distilled extract is poor. The choice of specific IgE or skin prick testing should be individualised to the patient and hypophosphataemia Milk 15 kUA/L 5 kUA/L reflect the advantages and limitations of each test and the (BMJ 2014;348:g3172) Peanut 14 kUA/L Not clearly established available expertise of the doctor involved (table 2).7 ЖЖUsing haemoglobin kUA/L=allergen specific KU/L A1c to diagnose type 2 Oral food challenge testing diabetes or to identify Table 2 | Advantages and disadvantages of skin prick and The ideal test to confirm or refute the diagnosis of immediate people at high risk of specific IgE testing of investigation of allergy* food allergy is the double blind placebo controlled food chal- diabetes Specific IgE testing Skin testing lenge carried out by specialist allergy services.8 Blinded chal- (BMJ 2014;348:g2867) Sensitive Often greater sensitivity than specific IgE lenges allow confident identification of clinical allergy and ЖЖInvestigation of Widely available Available in centres with appropriate reagents, exclude asymptomatic sensitisation and functional symp- equipment, and trained staff suspected urinary tract toms. This investigative strategy is particularly important infection in older people Results can take days to Results in 15 minutes, visible to patients weeks when the history and test results are ambiguous. In practice, (BMJ 2014;349:g4070) No interference from drugs Antihistamines, β blockers, and some specialist centres routinely provide unblinded challenges, ЖЖInterpreting raised antidepressants can interfere with results although access to these resource intensive investigations serum prolactin results Standardised laboratory Observer dependent might be rationed in some healthcare systems. Various pro- (BMJ 2014;348:g3207) assay tocols exist to perform these tests, but all challenge protocols ЖЖOrdering and Interference from high total No interference from high total IgE include the administration of increasing quantities of a pro- IgE can cause positive results posed allergen under medical supervision. Direct mucosal interpreting hepatitis B without clinical allergy exposure (allergen held to lip) is the first stage of the chal- serology *Adapted from the ASCIA manual: Skin Prick Testing for the Diagnosis of Allergic 8 lenge before titrated oral ingestion. In certain cases, after risk (BMJ 2014;348:g2522) Disease. stratification by experienced practitioners, home challenges The most common pitfall with specific IgE testing is the might be recommended.9 Failure to directly provoke symp- assumption that a positive test result confirms clinical allergy. toms will confidently exclude an allergy in most cases. Incorrect use of specific IgE as a screening test, without a compatible history, can lead to food allergy being errone- Outcome ously diagnosed.3 The consequences of incorrect diagnosis Based on the history and specific IgE results, the GP diag- can include an unnecessarily restricted diet and patient/ nosed egg allergy. By avoiding blanket/panel allergy testing, parental anxiety. Case reports have even described the loss of the GP avoided the common pitfall of detecting multiple, tolerance to foods because of prolonged inappropriate exclu- clinically irrelevant, low level positive specific IgE results. sion, leading to on re-introduction.4 Conversely, She did not prescribe an adrenaline auto-injector given the a negative specific IgE result can be used to inappropriately absence of anaphylaxis or severe comorbid conditions—such refute a diagnosis of allergy. A common example of this as poorly controlled —and the low incidence of life includes allergy to fruit and vegetables where the diagnostic threatening reactions to egg.9 For other allergens, an adren- performance characteristics of specific IgE testing are poor. In aline auto-injector can be considered in the absence of life recent years, component resolved diagnostics, which detect threatening features if there are comorbid conditions or the specific IgE to epitopes (those sites of an allergen to which allergen is difficult to avoid or has a high associated risk of antibody binds, such as Gal d1 in egg), have been investi- anaphylaxis (such as with peanut). A written management gated as an additional diagnostic and prognostic tools.5 The plan was agreed with the parents, clearly setting out the use clinical utility and cost effectiveness have not yet been fully of antihistamines for skin limited reactions after accidental evaluated and remain controversial, and the use of compo- exposure, and reasons to seek emergency help. Although this nent resolved diagnostics should be restricted to specialists. was the first exposure to scrambled egg (lightly cooked), the Box 2 | Which patients Requests for specific IgE testing must be tailored to the clini- GP noted that the child had previously eaten baked egg (well with egg allergy should be referred to an allergy cal history and involve an appreciation of its limitations. cooked) uneventfully and thus advised avoiding raw and clinic?10 lightly cooked egg in the diet, but continuing previously tol- Skin prick testing: limitations and difficulties in interpretation Children with systemic erated well cooked egg. She discussed the question of onward symptoms consistent with Skin prick testing identifies in vivo sensitisation to allergens. referral with the local paediatric allergy service. They agreed a severe reaction It can be performed in an outpatient setting and involves the that specialist assessment was not required at this stage as Children who have poorly epicutaneous introduction of allergen extracts with a stand- symptoms were limited to the skin, the child did not have controlled asthma or use ardised lancet.6 Typically the volar aspect of the forearm, or asthma, and the diagnosis was clear (box 2). Referral for a inhaled glucocorticoids the back in small infants, is used. The site is then inspected home based challenge to less well cooked egg, when the child regularly 15 minutes later and compared with suitable positive and reached 3-4 years, was planned, with the parents’ agreement. When the diagnosis is negative controls. A weal 3 mm greater in diameter than the Contributors: CS, NC, and JDE were responsible for the idea and conception of uncertain 4 the article. CS and NC drafted the article. CS, NC, and JDE reviewed and finally negative control is considered a positive test result ; smaller approved the article. JDE is guarantor. Persistent egg allergy yet still important weals can be observed in infants. Again, (beyond age 6-8) Competing interests: None declared. accurate interpretation of results requires an appropriate Provenance and peer review: Not commissioned; externally peer reviewed. Egg allergy with another clinical history. Skin prick tests can fail to show sensitisa- Patient consent not required (patient anonymised, dead, or hypothetical). major food allergy tion when antihistamines are used concurrently, and train- References are in the version on thebmj.com.

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