Positive serum specific IgE has a short half-life in patients with penicillin allergy and reversal does not always indicate tolerance

[Diagnostics of drug allergies and intolerances]

The prevalence of hypersensitivity reactions to drugs is increasing. Currently, this affects more than 7% of the world population. Nonsteroidal anti-inflammatory drugs (NSAID) and beta-lactam antibiotics (BLA) are by far the most common pharmaceutical preparations involved in hypersensitivity reactions to drugs. Misdiagnoses are frequent and BLA allergies present a danger that can lead to adverse health outcomes. Therefore, delabeling (exclusion of a suspected diagnosis) is paramount for those affected. Following the occurrence of uncomplicated maculopapular exanthemas, outpatient oral drug provocation can be safely considered in children without prior skin tests. Immediate perioperative reactions are rare. The approach to studying these complex reactions requires collaboration between allergologists and anesthesiologists to provide the best possible care for these patients.

Reliability of Early and Late Testing for Suspected Perioperative Hypersensitivity

BACKGROUND

The optimal timing of diagnostic testing for perioperative hypersensitivity (POH) remains unknown. It has been recommended that investigation is best carried out at least 4 to 6 weeks after the event. On the other hand, guidelines discourage the use of in vitro tests later than 3 years after the index reaction.

OBJECTIVE

This retrospective study aimed to assess the reliability of early and late skin tests (STs). It also attempted to verify whether discouraging late ex vivo and in vitro tests is substantiated.

METHODS

For the first aim, patients were stratified over three epochs: an early timing group, with investigations performed within 6 weeks; a recommended timing group, with tests performed between 6 weeks and 6 months; and a late timing group, tested later than 6 months after the event. For the second study purpose, we studied the reliability of specific IgE quantification and basophil activation test rocuronium within 6 weeks and after 3 years in patients who experienced an ST-proven POH to rocuronium.

RESULTS

A total of 677 patients were included. Based on a positive ST result, a causative agent was found in 74.2% of the early timing group, 62.6% of the recommended timing group, and 50% of the late timing group. A positive specific IgE for rocuronium or morphine was found in 80% of patients tested within 6 weeks, 63% of patients tested between 6 weeks and 3 years, and 50% of patients tested more than 3 years after the event. A positive basophil activation test was found in 83.3%, 51%, and 20%, respectively, of patients.

CONCLUSIONS

Our data confirm that evaluation of drug allergy for suspected POH can be performed before 6 weeks after the event, and there is no maximal upper time limit disclosing ex vivo and in vitro testing.

Isolierte Zungenschwellung nach Penizillin und negative Allergieabklärung – alles in Butter?

Penizilline können alle Arten spezifischer Immunreaktionen nach der erweiterten Coombs- und Gell-Klassifikation auslösen und zählen zu den häufigsten Ursachen unerwünschter Arzneimittelreaktionen. Das diagnostische Armamentarium umfasst neben den verschiedenen Hauttesten den Nachweis spezifischer IgE gegen allergene Determinanten am Betalaktam-Molekül und ggf. zelluläre Aktivierungsteste. Im Fall negativer Ergebnisse bei den genannten Testen kann ggf. noch die Toleranz im Rahmen eines Provokationstestes nachgewiesen werden. Die Sensitivität der diagnostischen Teste ist – mit Ausnahme des Provokationstests – aber limitiert, und falsch negative Teste sind möglich. Wir präsentieren zwei Fälle mit einer isolierten Zungenschwellung nach Gabe von Amoxicillin bei vollständig negativem, wiederholtem allergologischen Work-up. Bei beiden Patienten konnte die Überempfindlichkeit nur mit einer Reexposition nachgewiesen werden.

Allergy to polyethylene glycol and polysorbates in a patient cohort: Diagnostic work-up and decision points for vaccination during the COVID-19 pandemic

BACKGROUND

During the COVID-19 pandemic focus has been on polyethylene glycol (PEG) and polysorbate as these excipients are constituents in the first vaccines and possible elicitors of allergic reactions to the vaccines. We aimed to evaluate the possibility of vaccinating patients with PEG and/or polysorbate allergy against COVID-19.

METHODS

Twenty-five patients with a history of an allergic reaction to drugs, vaccines and mouth hygiene products containing PEG or polysorbate and sensitization (skin test or in vitro test) or a positive challenge were included. We re-evaluated 19 of 21 patients diagnosed before 2021 and four new patients by skin prick tests (SPT) and Basophil Histamine Release (BaHR) for PEGs, polysorbates and approved COVID-19 vaccines as well as measurement of specific IgE (PEG 2000, 10,000). Patients were offered vaccination based on decision points from the primary diagnosis and re-evaluation.

RESULTS

Most common primary elicitors were depot-steroids and laxatives. Most patients had experienced more than one reaction. SPT was superior to BaHR test although many SPTs became negative over time. After careful re-evaluation three patients were successfully vaccinated with the Pfizer/BioNTech vaccine. Three were vaccinated before referral. Eleven were offered the Johnson-Johnson vaccine; four were vaccinated successfully, seven abstained. Six patients could not be vaccinated with PEG or polysorbate containing vaccines.

CONCLUSION

Hypersensitivity to excipients in COVID-19 vaccines constitutes a risk to patients with allergy to PEG or polysorbates. After diagnostic evaluation, a safe COVID-19 vaccine could be offered to most patients, the remainders will await new vaccines containing different excipients.

Algorithm to guide re-exposure to penicillin in allergic pregnant women with syphilis: Efficacy and safety

Background

Gestational syphilis is underdiagnosed and undertreated, leading to stillbirth, prematurity, low birthweight, neonatal death, and congenital syphilis. Most patients who label as allergic to penicillin are misdiagnosed.

Objective

To assess the efficacy and safety of an algorithm to guide re-exposure to penicillin in pregnant women with syphilis and reporting allergy to the antibiotic.

Methods

We performed a prospective study assessing pregnant women with syphilis and labeled as allergic to penicillin. Based on clinical history, patients were divided in two groups: high-risk and low-risk to penicillin allergy. Low-risk patients with negative skin testing and negative serum specific IgE to penicillin underwent drug provocation test. The remaining patients underwent desensitization.

Results

Ninety-one patients were enrolled. Allergy to penicillin was confirmed in 7.69% of pregnant women with syphilis and clinical history of allergy to penicillin; in all cases the diagnosis was made through intradermal testing, which predicted 100% of the breakthrough reactions observed during rapid drug desensitization (p < 0.001). Risk stratification based on the initial clinical reaction and skin testing to guide penicillin re-introduction through drug challenge or desensitization was safe (97.8%) and effective (97.8%).

Conclusion

We developed and showed the efficacy and safety of an algorithm to guide re-exposure to penicillin in pregnant women with syphilis and labeled as allergic to this drug. Intradermal test is an excellent biomarker in the diagnosis of immediate hypersensitivity reaction to penicillin and to predict breakthrough reaction during rapid drug desensitization. Further studies may confirm the greater safety of the intravenous protocol compared to the oral protocol.

Minimal agreement between basophil activation test and immunoassay in diagnosis of penicillin allergy

INTRODUCTION

Basophil activation test (BAT) and immunoassays are the most widely used in vitro tests to diagnose IgE-mediated allergic reactions to penicillin. However, studies to determine if one test is interdependent from another are limited.

OBJECTIVE

The present study aimed to measure the agreement between BAT and immunoassay in diagnosis of penicillin allergy.

METHOD

BAT was performed using penicillin G (Pen G), penicillin V (Pen V), penicilloyl-polylysine (PPL), minor determinant mix (MDM), amoxicillin (Amx) and ampicillin (Amp) in 25 patients. Immunoassay of total IgE (tIgE) and specific IgE (sIgE) antibodies to Pen G, Pen V, Amx and Amp were quantified. Skin prick test (SPT) using PPL-MDM, Amx, Amp and Clavulanic acid were also performed.

RESULTS

Minimal agreement was observed between BAT and immunoassay (k=0.25). Of two BAT-positive patients, one patient is positive to Amx (59.27%, SI=59) and Amp (82.32%, SI=82) but sIgE-negative to all drug tested. This patient is also SPT-positive to both drugs. Another patient is BAT-positive to Pen G (10.18%, SI=40), Pen V (25.07%, SI=100) and Amp (19.52%, SI=79). In sIgE immunoassay, four patients were sIgE-positive to at least one of the drugs tested. The sIgE level of three patients was between low and moderate and they were BAT-negative. One BAT-positive patient had a high level of sIgE antibodies (3.50-17.5kU/L) along with relatively high specific to total IgE ratio ≥0.002 (0.004-0.007).

CONCLUSIONS

The agreement between BAT and immunoassay is minimal. Performing both tests provides little increase in the sensitivity of allergy diagnosis work-up for immediate reactions to penicillin.

Guideline on diagnostic procedures for suspected hypersensitivity to beta-lactam antibiotics: Guideline of the German Society for Allergology and Clinical Immunology (DGAKI) in collaboration with the German Society of Allergology (AeDA), German Society for Pediatric Allergology and Environmental Medicine (GPA), the German Contact Dermatitis Research Group (DKG), the Austrian Society for Allergology and Immunology (ÖGAI), and the Paul-Ehrlich Society for Chemotherapy (PEG)

This guideline on diagnostic procedures for suspected beta-lactam antibiotic (BLA) hypersensitivity was written by the German and Austrian professional associations for allergology, and the Paul-Ehrlich Society for Chemotherapy in a consensus procedure according to the criteria of the German Association of Scientific Medical Societies. BLA such as penicillins and cephalosporins represent the drug group that most frequently triggers drug allergies. However, the frequency of reports of suspected allergy in patient histories clearly exceeds the number of confirmed cases. The large number of suspected BLA allergies has a significant impact on, e.g., the quality of treatment received by the individual patient and the costs to society as a whole. Allergies to BLA are based on different immunological mechanisms and often manifest as maculopapular exanthema, as well as anaphylaxis; and there are also a number of less frequent special clinical manifestations of drug allergic reactions. All BLA have a beta-lactam ring. BLA are categorized into different classes: penicillins, cephalosporins, carbapenems, monobactams, and beta-lactamase inhibitors with different chemical structures. Knowledge of possible cross-reactivity is of considerable clinical significance. Whereas allergy to the common beta-lactam ring occurs in only a small percentage of all BLA allergic patients, cross-reactivity due to side chain similarities, such as aminopenicillins and aminocephalosporins, and even methoxyimino cephalosporins, are more common. However, the overall picture is complex and its elucidation may require further research. Diagnostic procedures used in BLA allergy are usually made up of four components: patient history, laboratory diagnostics, skin testing (which is particularly important), and drug provocation testing. The diagnostic approach - even in cases where the need to administer a BLA is acute - is guided by patient history and risk - benefit ratio in the individual case. Here again, further studies are required to extend the present state of knowledge. Performing allergy testing for suspected BLA hypersensitivity is urgently recommended not only in the interests of providing the patient with good medical care, but also due to the immense impact of putative BLA allergies on society as a whole.

The challenge of de-labeling penicillin allergy

BACKGROUND

Even though 8%-25% of most populations studied globally are labeled as penicillin allergic, most diagnoses of penicillin allergy are made in childhood and relate to events that are either not allergic in nature, are low risk for immediate hypersensitivity, or are a potential true allergy that has waned over time. Penicillin allergy labels directly impact antimicrobial stewardship by leading to use of less effective and broader spectrum antimicrobials and are associated with antimicrobial resistance. They may also delay appropriate antimicrobial therapy and lead to increased risk of specific adverse healthcare outcomes. Operationalizing penicillin allergy de-labeling into a new arm of antimicrobial stewardship programs (ASPs) has become an increasing global focus.

METHODS

We performed an evidence-based narrative review of the literature of penicillin allergy label carriage, the adverse effects of penicillin allergy labels, and current approaches and barriers to penicillin allergy de-labeling. Over the period 1928-2018 in Pubmed and Medline, search terms used included "penicillin allergy" or "penicillin hypersensitivity" alone or in combination with "adverse events," "testing," "evaluation," "effects," "label," "de-labeling," "prick or epicutaneous," and "intradermal" skin testing, "oral challenge or provocation," "cross-reactivity," and "antimicrobial stewardship".

RESULTS

Penicillin allergy labels are highly prevalent, largely inaccurate and their carriage may lead to unnecessary treatment and inferior outcomes with alternative agents as well as adverse public health outcomes such as antibiotic resistance.

CONCLUSIONS

Operationalizing penicillin allergy de-labeling as an aspect of ASP has become an increasing global focus. There is a need for validated approaches that optimally combine the use of history and ingestion challenge with or without proceeding formal skin testing to tackle penicillin allergy efficiently within complex healthcare systems. At the same time, there is great promise for penicillin allergy evaluation and de-labeling as an individual and public health strategy to reduce adverse healthcare outcomes, improve antimicrobial stewardship, and decrease healthcare costs.

Prospective assessment of diagnostic tests for pediatric penicillin allergy: From clinical history to challenge tests

BACKGROUND

Diagnostic guidelines for penicillin allergy in children recommend cumbersome protocols based partially on data from adults, which may be suboptimal for pediatric use.

OBJECTIVE

To assess the accuracy of tools for diagnosis of penicillin allergy in children.

METHODS

A prospective, multicenter study was conducted in children with reported adverse events related to penicillin, excluding severe reactions. All patients underwent a uniform diagnostic protocol that consisted of clinical history, skin tests, serum specific IgE (sIgE), and, regardless of these results, drug provocation tests (DPTs).

RESULTS

A total of 732 children (mean age, 5.5 years; 51.2% males) completed the allergy workup, including DPTs. Amoxicillin triggered 96.9% of all reactions. None of the patients with an immediate index reaction (IR) developed a reaction on DPT. Penicillin allergy was confirmed in 35 children (4.8%): 6 immediate reactions (17%) and 29 nonimmediate reactions (83%) on the DPT. No severe reactions were recorded. The allergist diagnosis based on the clinical history was not associated with the DPT final outcome. In 30 of 33 allergic patients (91%), the results of all skin tests and sIgE tests were negative. A logistic regression model identified the following to be associated with penicillin allergy: a family history of drug allergy (odds ratio [OR], 3.03; 95% confidence interval [CI], 1.33-6.89; P = .008), an IR lasting more than 3 days vs 24 hours or less (OR, 8.96; 95% CI, 2.01-39.86; P = .004), and an IR treated with corticosteroids (OR, 2.68; 95% CI, 1.30-5.54; P = .007).

CONCLUSION

Conventional predictors of allergy to penicillin performed weakly. The authors propose straightforward penicillin provocation testing in controlled, experienced centers for the diagnosis of nonsevere penicillin allergy in children.

Antibiotic Allergy in Pediatrics

The overlabeling of pediatric antibiotic allergy represents a huge burden in society. Given that up to 10% of the US population is labeled as penicillin allergic, it can be estimated that at least 5 million children in this country are labeled with penicillin allergy. We now understand that most of the cutaneous symptoms that are interpreted as drug allergy are likely viral induced or due to a drug-virus interaction, and they usually do not represent a long-lasting, drug-specific, adaptive immune response to the antibiotic that a child received. Because most antibiotic allergy labels acquired in childhood are carried into adulthood, the overlabeling of antibiotic allergy is a liability that leads to unnecessary long-term health care risks, costs, and antibiotic resistance. Fortunately, awareness of this growing burden is increasing and leading to more emphasis on antibiotic allergy delabeling strategies in the adult population. There is growing literature that is used to support the safe and efficacious use of tools such as skin testing and drug challenge to evaluate and manage children with antibiotic allergy labels. In addition, there is an increasing understanding of antibiotic reactivity within classes and side-chain reactions. In summary, a better overall understanding of the current tools available for the diagnosis and management of adverse drug reactions is likely to change how pediatric primary care providers evaluate and treat patients with such diagnoses and prevent the unnecessary avoidance of antibiotics, particularly penicillins.

Occupational generalized urticaria and anaphylaxis after inhalation of cefuroxime in a nurse

We present the case of a 53 years old nonatopic female nurse who experienced repeated anaphylactic reactions at work without involvement in drug-specific tasks such as crushing of tablets or preparation of injections. The causal allergen was not identified until a further severe anaphylactic reaction occurred after oral use of cefuroxime during a respiratory infection. Sensitization to cefuroxime was demonstrated by specific IgE, basophil activation test and skin prick test. An inhalation challenge with a dosimeter induced generalized urticaria after a cumulative dose of about 10 μg of the drug, but no asthmatic reaction. Complete exposure cessation was initiated and a 1-year follow-up was without further allergic reactions. We conclude that work-related systemic allergic reactions to β-lactam antibiotics may occur in nurses after inhalation of low doses and without perceived association with drug-specific tasks like handling of antibiotics.

Positive Skin Test or Specific IgE to Penicillin Does Not Reliably Predict Penicillin Allergy

INTRODUCTION

According to guidelines, patients are diagnosed with penicillin allergy if skin test (ST) result or specific IgE (s-IgE) to penicillin is positive. However, the true sensitivity and specificity of these tests are presently not known.

OBJECTIVE

To investigate the clinical relevance of a positive ST result and positive s-IgE and to study the reproducibility of ST and s-IgE.

METHODS

A sample of convenience of 25 patients with positive penicillin ST results, antipenicillin s-IgE results, or both was challenged with their culprit penicillin. Further 19 patients were not challenged, but deemed allergic on the basis of a recent anaphylactic reaction or delayed reactions to skin testing. Another sample of convenience of 18 patients, 17 overlapping with the 25 challenged, with initial skin testing and s-IgE (median, 25; range, 3-121), months earlier (T_-1), was repeat skin tested and had s-IgE measured (T₀), and then skin tested and had s-IgE measured 4 weeks later (T₁).

RESULTS

Only 9 (36%) of 25 were challenge positive. There was an increased probability of being penicillin allergic if both ST result and s-IgE were positive at T₀. Positive ST result or positive s-IgE alone did not predict penicillin allergy. Among the 18 patients repeatedly tested, 46.2% (12 of 25) of positive ST results at T_-1 were reproducibly positive at T₀. For s-IgE, 54.2% (14 of 24) positive measurements were still positive at T₀ and 7 converted to positive at T₁.

CONCLUSIONS

The best predictor for a clinically significant (IgE-mediated) penicillin allergy is a combination of a positive case history with simultaneous positive ST result and s-IgE or a positive challenge result.

Passive blood anaphylaxis: subcutaneous immunoglobulins are a cause of ongoing passive anaphylactic reaction

Background

Allergic, especially anaphylactic, reactions during immunoglobulin replacement therapy are rare, but their pathophysiology and classification remain ambiguous. Recent findings show positive results of skin tests with commercially available immunoglobulins, but target antigens and responsible compounds of the tested immunoglobulins have not been strictly identified.

Case description and findings

Four adult patients with recently diagnosed common variable immunodeficiency qualified for standard subcutaneous immunoglobulin replacement therapy regimen. They had no history of receiving immunoglobulins, blood or blood product transfusions. Edema, confluent wheals and erythema were observed at the site of subcutaneous immunoglobulin infusion: typical early and late phase reaction. A transient increase in various passively transferred IgG and IgE antibodies was responsible for misleading positive outcome of the serological testing for active humoral response such as type I allergy, anti-Rh, isohemagglutinins and rheumatoid factor (RF). Although the clinical presentation was very unusual and severe, the retrospective analysis showed no isohemagglutinins, RF and IgE in the patients’ serum before but it was positive after the infusion (median IgE = 18 IU/ml, RF = 8 IU/ml). Type I allergic reaction (laryngeal edema, rhinoconjuctivitis) came out at +14 days of replacement therapy when the patient visited countryside. In the second patient anaphylactic reaction was observed 5 days after ScIg administration, and only when the patient consumed peanuts. Therefore, IgE concentration was measured retrospectively in a series of commercial preparations used in the initial subcutaneous immunoglobulin replacement therapy that caused the adverse event (AE) and it was determined between 138 and 232 IU/ml (kU/l), i.e. 690–2100 IU per g of protein. Specific IgE was within a wide range from 198 (mix of food) to 2809 kUA/l (mix of grass) but many of the tested allergen-specific IgE were class 2 or 3 (i.e. 0.71–17.5 kUA/l).

Conclusions

The case resembles passive cutaneous anaphylaxis and Prausnitz–Küstner reaction but clinical significance of the classical phenomena has not yet been described. This observation indicates that anaphylactic reactions during immunoglobulin replacement therapy may result from IgE or pathological IgG content. Such IgE presence was sporadically reported (34.5–105 IU/ml, i.e. 862.5–1450 IU/g of protein) in intravenous immunoglobulins that are used and monitored by healthcare professionals. In clinical practice the definition of adverse events is inadequate since individual batches of immunoglobulins come with different specificity therefore, they should be classified as transfusion products (not bioequivalents). Such new approach implies establishing (1) new control methods and strategies to ensure introduction of the safety regulations for subcutaneous home self-administration of immunoglobulins as well as (2) guidelines for the prevention of anaphylaxis in patients receiving immunoglobulins (for example peanut).

Allergy test outcomes in patients self-reported as having penicillin allergy: Two-year experience

BACKGROUND

Penicillin allergy is associated with increased antibiotic resistance and health care costs. However, most patients with self-reported penicillin allergy are not truly allergic.

OBJECTIVE

To summarize our experience with allergy tests in patients with a history of penicillin allergy and to compare them with the results of other groups.

METHODS

We retrospectively reviewed all patients with a suspected clinical history of penicillin allergy referred to the Drug Allergy Unit at University College London Hospital between March 2013 and June 2015.

RESULTS

In total, 84 patients were reviewed. The index drugs included: unidentified penicillin (n = 44), amoxicillin (n = 17), amoxicillin-clavulanic acid (n = 13), flucloxacillin (n = 4), and other penicillins (ampicillin, benzylpenicillin, piperacillin-tazobactam; n = 7). Allergy diagnoses were confirmed in 24 patients (28.6%) (16 to penicillin, 3 to flucloxacillin, 5 to clavulanic acid). Twenty-two patients (91.7%) had allergy diagnosed by positive skin test results. Two patients (8.3%) developed IgE-mediated allergic symptoms during oral challenge (although the skin test results were negative). In vitro specific IgE test results for penicilloyl V, penicilloyl G, and amoxicilloyl were positive in 3 of 16 patients (18.8%). Moreover, reactions to cefuroxime were observed in 3 of 15 patients with penicillin allergy (20%). Selective clavulanic acid and flucloxacillin responders tolerated amoxicillin challenge. The interval between the index reaction and evaluation was shorter (P < .001), and the proportion of patients who could recall the name of the culprit drug was higher (P = .009) in the allergic group. Furthermore, histories of anaphylaxis (33.3%), urticaria, and/or angioedema (58.3%) were more common in the allergic group. Unspecified rashes (35.0%) and nonspecific symptoms (28.3%) predominated in the nonallergic group.

CONCLUSION

Only 28.6% of patients with self-reported penicillin allergy were confirmed to be allergic. Importantly, when the index drug is amoxicillin-clavulanic acid or flucloxacillin, the patients may tolerate amoxicillin.

Three cases of anaphylaxis following injection of a depot corticosteroid with evidence of IgE sensitization to macrogols rather than the active steroid

We present three cases with anaphylaxis after injection of a depot corticosteroid. First, the steroid was suspected as the elicitor, but after evaluation the excipient macrogol was found to be the elicitor. One of the patients had reactions to several unrelated drugs. Increased awareness of anaphylaxis to excipients such as macrogols is needed, especially when allergy tests for the active drug is negative and in patients with a history of repeated anaphylaxis to seemingly unrelated drugs. To establish the correct diagnosis it is important to test with the exact formulation of the culprit drug, as well as all the ingredients including excipients.

Dynamics of plasma levels of specific IgE in chlorhexidine allergic patients with and without accidental re-exposure

BACKGROUND

Chlorhexidine is an effective disinfectant, which may cause severe allergic reactions. Plasma level of specific IgE to chlorhexidine (ImmunoCAP(®) ) has high estimated sensitivity and specificity when measured within 6 months of allergic reaction, but knowledge of the dynamics over longer time periods is lacking and it is unknown whether levels fall below <0.35 kUA/L in patients with previously elevated levels. It is also unclear whether re-exposure influences levels of specific IgE.

OBJECTIVE

To investigate the dynamics of specific IgE in chlorhexidine allergic patients with and without re-exposure.

METHODS

All patients diagnosed with chlorhexidine allergy in the Danish Anaesthesia Allergy Centre January 1999 to March 2015 were invited to participate. The study included blood samples from the time of reaction and time of investigation and blood samples drawn prospectively over several years.

RESULTS

Overall, 23 patients were included. Specific IgE within hours of reaction was available in eight patients and was >0.35 kUA/L in six of these. During allergy investigations, usually 2-4 months later, specific IgE was >0.35 kUA/L in 22 of 23 patients. In the following months/years specific IgE declined <0.35 kUA/L in 17 of 23 patients (most rapidly within 4 months). Nine re-exposures in the healthcare setting were reported by seven patients (35%). Most re-exposures caused symptoms and were followed by an increase in specific IgE. Two patients with specific IgE <0.35 kUA/L reacted upon re-exposure.

CONCLUSIONS & CLINICAL RELEVANCE

Time from reaction should be considered when interpreting specific IgE results. Specific IgE is >0.35 kUA/L in most patients at time of reaction but should be repeated after a few weeks/months if negative. The optimal sampling time seems to be >1 month and <4 months. A value <0.35 kUA/L neither excludes allergy nor implies loss of reactivity in previously sensitized patients. Re-exposures are common, often iatrogenic, and can cause a rebound in specific IgE.