The Who, What, When, and Where of Inpatient Direct Oral Penicillin Challenge-Implications for Health Services Implementation.

Inpatient direct oral challenge programs are increasingly deployed as part of antimicrobial stewardship initiatives to reduce the burden and impacts of penicillin allergy labels on antibiotic prescribing. Using data from a prospective, multicenter cohort inpatient penicillin allergy program, we identify the key targets for delabeling to aid health service implementation.

Beta-lactam hypersensitivity in children: Frequency and risk factors.

AIMS: To determine the frequency of an authentic ß-lactam (BL) hypersensitivity (HS) amongst a large number of children and to identify clinical risk factors that predict this hypersensitivity. METHODS: All children with suspected BL allergy were evaluated by skin tests (ST) with the suspected BL. A 1-day oral provocation test (OPT) was performed in children with negative ST. We defined an authentic BL-HS case if the child exhibited a positive ST or a positive OPT. Risk factors associated with BL-HS were assessed using a univariate analysis. Covariates showing a P-value <.2 were included in the multivariate logistic regression analysis to determine independent predictors. RESULTS: A total of 354 patients reporting 368 suspected BL reactions were included. The diagnosis of BL-HS was established in 24 children (6.7%). All these children had a positive ST. OPT was performed in 30 patients and was negative in all of them. In 110 children with a negative ST, BL was tolerated. In the risk factors analysis, 164 children were included. Older age (>5 years) at the reaction (odds ratio = 1.11; 95% confidence interval, 1.01-1.22; P = .02) and BL administered (odds ratio = 7.7; 95% confidence interval, 2.76-21.8; P < .001) were significantly associated with authentic BL-HS. CONCLUSION: BL-HS should be evaluated with an appropriate allergy work-up before strict prohibition is made. In addition, age of patient and BL involved can be used as predictive factors of developing BL-HS in this population.

Recent Updates in Understanding NSAID Hypersensitivity.

PURPOSE OF REVIEW: To provide a review of available literature regarding nonsteroidal anti-inflammatory drug (NSAID) hypersensitivity with an emphasis on more recent findings. RECENT FINDINGS: Oral provocation tests with aspirin are important for diagnosis and management in adult and pediatric populations with reported NSAID hypersensitivity. Risk of cross-reactivity to COX-2 inhibitors varies by NSAID hypersensitivity phenotype. COX-2 inhibitors are tolerated in aspirin-exacerbated respiratory disease. Reported NSAID allergy is associated with a higher risk of a substance use disorder. Effective treatment of underlying chronic spontaneous urticaria can allow tolerance of NSAIDs in NSAID-exacerbated cutaneous disease. The pathophysiology, cross-reactivity, and appropriate diagnostic evaluation differ between the 5 distinct NSAID hypersensitivity phenotypes. Further research into the pathophysiology of NSAID hypersensitivity in patients with and without underlying disease is needed.

Antibiotic oral provocation challenge in children.

AIM: The main objective of this study was to see how many of the children, with a suspected antibiotic allergy, developed an allergic or adverse reaction to a drug provocation test. METHODS: Data on children that had undergone a drug provocation test for a suspected antibiotic allergy were compiled retrospectively for the period from 2007-2018. The median age at the first provocation was 2.25 years (1.5-5.7). Standardised questionnaires, the children's parents had answered before the provocation, were used to evaluate the originally suspected allergic reaction, previous health, atopic diseases and family history. RESULTS: Ninety-two (6.4%) of the 1440 children showed a possible mild allergic reaction. Sixty-four of the 92 children underwent a second drug provocation test 1-2 years later. At that time, only eleven developed a positive- or a possible-delayed reaction. CONCLUSION: An immediate moderate or severe allergic reaction was excluded in all cases of suspected antibiotic allergy in this study. Our study indicates that an oral drug provocation test is safe. It may be appropriate to wait for 6 months or more after the initial event of ADR before these tests are performed. A second oral provocation 1-2 years after the first one shows that ADRs are outgrown in most children.

Meloxicam and/or Etoricoxib Could Be Administered Safely in Two Equal Doses during an Open Oral Challenge in Patients with Nonsteroidal Anti-Inflammatory Drug Hypersensitivity.

BACKGROUND: Hypersensitivity reactions to nonsteroidal anti-inflammatory drugs (NSAIDs) are common. These patients require an effective and safe analgesic alternative. OBJECTIVE: The aim of the study was to demonstrate the safety of meloxicam and etoricoxib administered by open oral challenge in 2 equal steps in patients with NSAID hypersensitivity. METHODS: A cross-sectional, descriptive study of patients with a diagnosis of NSAID hypersensitivity who underwent an oral drug provocation test (DPT) with meloxicam or etoricoxib between January 2011 and August 2017 was conducted. The analysis was performed from a database in BD Clinic. RESULTS: Two hundred and twenty-eight oral provocations were performed with an alternative NSAID (203 with meloxicam and 25 with etoricoxib) in 217 patients with hypersensitivity to NSAIDs. The median age was 38 years. Ninety-eight percent of meloxicam and 100% of etoricoxib DPTs were performed in 2 steps (without previous placebo), and 52% and 64% of meloxicam and etoricoxib DPTs, respectively, were performed with 50% of the therapeutic dose in each step. Tolerance to meloxicam was demonstrated in 192 patients (94.5%) and in 100% of patients receiving etoricoxib. CONCLUSIONS: Open oral provocation with meloxicam and etoricoxib carried out in 2 steps without placebo seems to be safe and implies less costs and less time expenditure. Also, it could be performed with 2 equal doses.

Clarithromycin hypersensitivity in children: Is there a link with ß-lactam hypersensitivity?

BACKGROUND: Clarithromycin hypersensitivity is reported as the most common cause of non-ß-lactam antibiotic allergy in children. Clarithromycin is frequently prescribed in cases of suspected ß-lactam hypersensitivity. Oral provocation tests stand as the gold standard to confirm drug hypersensitivity as diagnostic value of skin tests is variable. We analyzed the frequency of true clarithromycin hypersensitivity ratio and its relationship with ß-lactam allergy among children with suspected clarithromycin hypersensitivity and evaluated the diagnostic value of skin tests. METHODS: The study included 160 children referred with suspected clarithromycin hypersensitivity. Clinical history and allergy workups including skin tests or/and oral provocation tests were retrieved from medical records. RESULTS: Oral provocation test confirmed clarithromycin hypersensitivity rate was 5.6% (n = 9/160). Skin tests with clarithromycin showed positivity in 32.6% (n = 29/89) of the tested patients. The sensitivity of clarithromycin skin tests was negligible, and specificity was 73.9% (95% confidence interval [CI], 64.7-81.8). Eighty-eight of the patients (55%) reported that they had previously tolerated a ß-lactam antibiotic. ß-lactam hypersensitivity was suspected in 40% (n = 64/160) of the patients (simultaneous [n = 10], sequential [n = 19], distant form [n = 35]) in relation with clarithromycin usage. ß-lactam hypersensitivity (95% CI, 2.1-70.6, p = .005) and sequential usage of clarithromycin after the development of a rash with amoxicillin-clavulanic acid (95% CI, 2.0-96.4, p = .007) were found as risk factors for confirmed clarithromycin hypersensitivity. CONCLUSION: The frequency of confirmed clarithromycin hypersensitivity was found low among suspected patients. Oral provocation test is crucial for definite diagnosis. Confirmed ß-lactam allergy may be attributed as a risk factor for clarithromycin hypersensitivity, particularly clarithromycin treatment after a developing rash with amoxicillin-clavulanic acid in sequential usage.

Critically appraised topic on adverse food reactions of companion animals (9): time to flare of cutaneous signs after a dietary challenge in dogs and cats with food allergies.

BACKGROUND: At this time, elimination diets followed by oral food challenges (OFCs) represent the "gold standard" for diagnosing skin-manifesting food allergies (FA) in dogs and cats. Regrettably, there is no clear consensus on how long one should wait for clinical signs to flare after an OFC before diagnosing or ruling-out a FA in a dog or a cat. RESULTS: We searched two databases on October 23, 2019 to look for specific information on the time for a flare of clinical signs to occur during OFCs after elimination diets in dogs and cats with skin-manifesting FAs. Altogether, we reviewed the study results of nine papers that included 234 dogs and four articles containing data from 83 cats. As multiple OFCs could be done in the same patient and not all animals included were subjected to an OFC, we were able to compile 315 and 72 times to flare (TTF) after an OFC in dogs and cats, respectively. When regrouping all cases together, about 9% of dogs and 27% of cats exhibited a flare of clinical signs in the first day after an OFC; 21% of dogs and 29% of cats had such relapse by the end of the second day. The time needed for 50 and 90% of dogs to exhibit a deterioration of clinical signs (TTF50 and TTF90) was 5 and 14, respectively; in cats, these times were 4 and 7 days, respectively. By 14 days after an OFC, nearly all food-allergic patients from both species had had a relapse of clinical signs. These results are limited by the likely under-reporting of flares that occur on the first day immediately following an OFC, the time in which IgE-mediated acute allergic reactions typically develop. CONCLUSION: Veterinary clinicians performing an OFC need to wait for 14 and 7 days for more than 90% of dogs and cats with a skin-manifesting FA to have a flare of clinical signs, respectively.

The first case of tegoprazan-induced urticaria.

WHAT IS KNOWN AND OBJECTIVE: Tegoprazan induces adverse drug reactions during clinical trials; however, tegoprazan-induced urticaria has not been reported. Here, we describe the first case of this. CASE DESCRIPTION: A 55-year-old woman presented with acute urticaria with pruritus after taking the gastro-oesophageal reflux disease medication, tegoprazan. Urticaria disappeared after tegoprazan discontinuation. In an oral provocation test, after taking 10% of tegoprazan, she developed pruritus, and after taking 30%, she developed urticaria on her back. WHAT IS NEW AND CONCLUSION: This is the first case of urticaria induced by tegoprazan. Physicians should understand the possibility of a tegoprazan-induced hypersensitivity reactions.

Milk processing increases the allergenicity of cow's milk-Preclinical evidence supported by a human proof-of-concept provocation pilot.

BACKGROUND: Several studies demonstrated the adverse effect of milk processing on the allergy-protective capacity of raw cow's milk. Whether milk processing also affects the allergenicity of raw milk is hardly investigated. OBJECTIVE: To assess the allergenicity of raw (unprocessed) and processed cow's milk in a murine model for food allergy as well as in cow's milk allergic children. METHODS: C3H/HeOuJ mice were either sensitized to whole milk (raw cow's milk, heated raw cow's milk or shop milk [store-bought milk]) and challenged with cow's milk protein or they were sensitized and challenged to whey proteins (native or heated). Acute allergic symptoms, mast cell degranulation, allergen-specific IgE levels and cytokine concentrations were determined upon challenge. Cow's milk allergic children were tested in an oral provocation pilot with organic raw and conventional shop milk. RESULTS: Mice sensitized to raw milk showed fewer acute allergic symptoms upon intradermal challenge than mice sensitized to processed milk. The acute allergic skin response was low (103 ± 8.5 µm vs 195 ± 17.7 µm for heated raw milk, P < 0.0001 and vs 149 ± 13.6 µm for shop milk, P = 0.0316), and there were no anaphylactic shock symptoms and no anaphylactic shock-induced drop in body temperature. Moreover, allergen-specific IgE levels and Th2 cytokines were significantly lower in raw milk sensitized mice. Interestingly, the reduced sensitizing capacity was preserved in the isolated native whey protein fraction of raw milk. Besides, native whey protein challenge diminished allergic symptoms in mice sensitized to heated whey proteins. In an oral provocation pilot, cow's milk allergic children tolerated raw milk up to 50 mL, whereas they only tolerated 8.6 ± 5.3 mL shop milk (P = 0.0078). CONCLUSION AND CLINICAL RELEVANCE: This study demonstrates that raw (unprocessed) cow's milk and native whey proteins have a lower allergenicity than their processed counterparts. The preclinical evidence in combination with the human proof-of-concept provocation pilot provides evidence that milk processing negatively influences the allergenicity of milk.

Immediate-Type Hypersensitivity Cross-Reactions to Proton Pump Inhibitors: A Descriptive Study of Data from the French National Pharmacovigilance Database.

BACKGROUND: Proton pump inhibitors (PPIs) can trigger immediate-type hypersensitivity reactions (HSRs). Three main patterns of cross-reactivity have been identified: reactions to a single PPI, selective cross-reactions, and cross-reactions with all PPIs. Several hypotheses have been advanced, but no consensus has been reached. OBJECTIVE: We sought to identify immediate-type hypersensitivity cross-reactions to PPIs using real-world data about hypersensitivity testing from French pharmacovigilance cases. METHODS: Potentially relevant immediate-type HSRs reported from January 1985 to February 2015 were extracted from the French pharmacovigilance database using a standardized MedDRA query (SMQ). Cases describing skin tests or oral provocation tests (OPTs) performed with several PPIs that yielded at least one positive result were included. RESULTS: The SMQ extracted 2,119 cases, 38 of which were included in our study. Data collected from skin tests and OPTs indicated cross-reactions with all PPIs (n = 1), reactions to a single PPI (n = 14), or selective cross-reactions (n = 23). Esomeprazole, omeprazole, and pantoprazole concerned 78% of all selective cross-reactions. In more than half of the cases (55.3%), only 2 PPIs were tested. CONCLUSION: To the best of our knowledge, this PPI cross-reactivity study is the largest to date in terms of population size, describing 38 immediate-type HSRs to PPIs explored by skin tests or OPTs. This paucity of data belies the lack of standardized procedures for PPI hypersensitivity testing. It is likely that PPI HSR workups in everyday clinical practice are often incomplete. Further research to gain insight into selective cross-reactions between PPIs is needed. In the meantime, thorough workups should be completed when a PPI is suspected to have triggered an HSR, instead of routine contraindication to all PPIs.

The Oral Provocation Test for Raw Egg in Patients with Hen Egg Allergy.

BACKGROUND: Many researchers have made efforts to develop diagnostic tools for predicting the outcome of oral food challenges (OFCs). The aim of this study was to assess the diagnostic value of the skin prick test (SPT) and blood-specific IgE concentrations based on the outcome of the OFCs for heated and raw hen egg. METHODS: This study included 103 children with suspected hen egg allergy (HEA; median age 23 months, range 10-155; 72 boys, 31 girls). Forty-three patients were diagnosed with HEA by OFC. Of 60 patients who tolerated heated egg white (HEW), 22 underwent the OFC for raw hen egg and 7 developed adverse reactions after ingesting raw egg. Their wheal diameters and specific IgE levels for egg white and ovomucoid were determined. RESULTS: Wheal diameters as well as blood-specific IgE levels for egg white and ovomucoid were significantly larger in children with positive OFC results for HEW than in those with negative results. However, there were no significant differences between the positive and negative test results for raw hen egg white (REW) in wheal diameter or blood-specific IgE levels. CONCLUSIONS: The SPT and blood-specific IgE can be used to diagnose HEA. However, the provocation test for REW in children without HEW allergy is important because the values of SPT and specific IgE were not significantly different between children with and without raw egg allergy.

Direct oral provocation tests in non-immediate mild cutaneous reactions related to beta-lactam antibiotics.

BACKGROUND: Skin testing has a limited role in the diagnosis of non-immediate beta-lactam hypersensitivity in children. The aim of this study was to report the results of oral provocation tests performed without skin tests in children with non-immediate mild cutaneous reactions without systemic symptoms caused by beta-lactam antibiotics. METHODS: Oral provocation tests with suspected antibiotics were performed to patients with non-immediate mild cutaneous reactions without systemic symptoms caused by beta-lactam antibiotics. Skin tests were not performed before provocation tests. A total of five doses were administered with half-an-hour intervals in increasing doses. Provocation was continued for 5 days. RESULTS: A total of 119 patients with a median age of 4.3 (IQR: 2-7.5) years, of whom 58% were males, were included in the study. Amoxicillin-clavulanic acid was the most frequently responsible agent in 87 (73.1%) patients, and most common type of rash was maculopapular in 74 (62.2%) patients. Four patients (3.4%) had an urticarial reaction during the provocation test. CONCLUSION: We did not experience any severe reactions during oral provocation test without previous skin tests performed to children with non-immediate mild cutaneous reactions without systemic symptoms. Omitting skin tests before oral provocation test in this group of children can help decreasing the burden of allergy clinics and alleviating the discomfort of children.

[Food allergy in adulthood]. / Nahrungsmittelallergie im Erwachsenenalter.

Food allergies can newly arise in adulthood or persist following a food allergy occurring in childhood. The prevalence of primary food allergy is basically higher in children than in adults; however, in the routine practice food allergies in adulthood appear to be increasing and after all a prevalence in Germany of 3.7 % has been published. The clinical spectrum of manifestations of food allergies in adulthood is broad. Allergy symptoms of the immediate type can be observed as well as symptoms occurring after a delay, such as indigestion, triggering of hematogenous contact eczema or flares of atopic dermatitis. The same principles for diagnostics apply in this group as in childhood. In addition to the anamnesis, skin tests and in vitro tests, as a rule elimination diets and in particular provocation tests are employed. Molecular allergy diagnostics represent a major step forward, which allow a better assessment of the risk of systemic reactions to certain foodstuffs (e.g. peanuts) and detection of cross-reactions in cases of apparently multiple sensitivities. Current German and European guidelines from 2015 are available for the practical approach to clarification of food allergies. The most frequent food allergies in adults are nuts, fruit and vegetables, which can cross-react with pollen as well as wheat, shellfish and crustaceans. The therapy of allergies involves a consistent avoidance of the allogen. Detailed dietary plans are available with avoidance strategies and instructions for suitable food substitutes. A detailed counseling of affected patients by specially trained personnel is necessary especially in order to avoid nutritional deficiencies and to enable patients to enjoy a good quality of life.

Single NSAID hypersensitivity is associated with atopic status.

BACKGROUND: The relationship between hypersensitivity to NSAID and atopic status is still incompletely defined. Previous studies found a high prevalence of atopic diseases in multiple NSAID reactors. The present study aimed to investigate whether this is the case also in Italian adults hypersensitive to NSAIDs. METHODS: Skin tests with a large panel of seasonal and perennial airborne allergens were carried out in 252 patients with a clear-cut history of acute urticaria induced by nonsteroidal anti-inflammatory drugs. Patients were classified as single or multiple NSAID reactors based on clinical history, presence/absence of chronic urticaria, re-challenge with the reported offending drug in case of doubt history, and oral challenges with aspirin or propionic acid derivatives. RESULTS: Single NSAID reactors showed a much higher prevalence of atopic diseases than multiple NSAID reactors either with or without chronic urticaria (61% vs 19% and 19%, respectively; p < 0.001). CONCLUSION: As a difference from previous reports, in Italian patients hypersensitive to NSAID atopy is much more prevalent among single reactors, a finding that indirectly supports the possible IgE-mediated origin of this type of adverse drug reaction.

Oral challenge vs routine care to assess low-risk penicillin allergy in critically ill hospital patients (ORACLE): a pilot safety and feasibility randomised controlled trial.

PURPOSE: Critically ill patients are vulnerable to penicillin allergy labels that may be incorrect. The validity of skin testing in intensive care units (ICUs) is uncertain. Many penicillin allergy labels are low risk, and validated tools exist to identify those amenable to direct oral challenge. This pilot randomised controlled trial explored the feasibility, safety, and validity of direct enteral challenge for low-risk penicillin allergy labels in critical illness. METHODS: Consenting patients with a low-risk penicillin allergy label (PAL) (PEN-FAST risk assessment score < 3) in four ICUs (Melbourne, Australia) were randomised 1:1 to penicillin (250 mg amoxicillin or implicated penicillin) direct enteral challenge versus routine care (2-h post-randomisation observation for each arm). Repeat challenge was performed post -ICU in the intervention arm. Patients were reviewed at 24 h and 5 days after each challenge/observation. RESULTS: We screened 533 patients. 130 (24.4%) were eligible and 80/130 (61.5%) enrolled (age median 64.5 years (interquartile range, IQR 53.5, 74), PEN-FAST median 1 (IQR 0,1)), with 40 (50%) randomised to direct enteral challenge. A positive challenge rate of 2.5% was identified. No antibiotic-associated serious adverse events were identified. 32/40 (80%) received a repeat challenge (zero positive). Post-randomisation, 13 (32%) of the intervention arm and 4 (10%) of the control arm received penicillin (odds ratio, OR 4.33 [1.27, 14.78] p = 0.019). CONCLUSION: These findings support the safety, validity, and feasibility of direct enteral challenge for critically ill patients with PEN-FAST assessed low-risk penicillin allergy. The absence of false negative results was confirmed by subsequent negative repeat challenges. A relatively low recruitment to screened ratio suggests that more inclusive eligibility criteria and integration of allergy assessment into routine ICU processes are needed to optimise allergy delabelling in critical illness.

First-Line Antituberculosis Drug Challenge Reactions in Drug Reaction with Eosinophilia and Systemic Symptoms Syndrome in an HIV Endemic Setting.

BACKGROUND: In high HIV prevalence settings, first-line antituberculosis drug (FLTD)-associated drug reaction with eosinophilia and systemic symptoms (DRESS) poses therapeutic challenges. A sequential and additive drug challenge (SADC) of FLTDs best identifies offending drug(s), avoids unnecessary exclusions, and optimizes reinitiation of nonoffending drugs. However, SADC-associated reaction complexities limit its utility. OBJECTIVE: We aimed to describe the characteristics of patients with FLTD-associated DRESS, their treatment-limiting SADC reactions, and related outcomes. METHODS: Patients hospitalized with FLTD-associated DRESS from 2013 to 2023 in a South African tertiary hospital and enrolled (retrospectively or prospectively) in an existing registry were eligible. RESULTS: SADC was undertaken in 41 patients. Overall, 47 classifiable reactions occurred. 34/47 (72%) reactions in 29/41 (71%) patients were treatment-limiting and 12 of 41(29%) patients reinitiated FLTDs uneventfully. Fifteen single and 8 multiple drug reactors were identified. Rifampicin in 13 of 23(57%) reactors was the most common individual offender. Ethambutol was most frequently involved in multiple drug reactors. The median (interquartile range) time to a detectable reaction was 24(12-120) hours, 6 of 34(18%) being immediate (<6 hours). Itch (65%), eosinophilia (56%), fever (41%), atypical lymphocytosis (41%), rash (38%), transaminitis (32%), and facial edema (18%) singly or in combination were the most common features. Three reactions, 1 epidermal necrolysis and 2 liver derangements, were Common Terminology Criteria for Adverse Events grade 4 (life-threatening) events. No predictors of multiple drug reactivity were identified, but multiple reactors were hospitalized significantly longer, 125(100-134) days versus 60(45-80) days. CONCLUSIONS: SADC optimizes FLTD reinitiation. However, timing, clinical presentation, and severity of SADC-associated reactions after FLTD-associated DRESS are markedly heterogeneous. Additionally, multiple drug reactors are a complex group that require longer hospitalization. There are no routine biomarkers available to distinguish true multiple drug hypersensitivity from nonspecific flare-ups and to guide long-term drug avoidance strategies.

Drug reintroduction testing and beta-lactam hypersensitivity in children: Protocols and results, a 12-year experience.

Introduction: Oral provocation test (OPT) to beta-lactam antibiotics (BL) is a gold standard in allergology investigation. We aimed to demonstrate the contribution of OPT in BL hypersensitivity (HS) indicated as a first step in diagnosis. Methods: We conducted a retrospective study from 2007 to 2019, in a single Tunisian tertiary care academic center. It concerned children with presumed non-severe allergic manifestations to BL, with a reaction that has occurred at least 6 months before the OPT. Results: We identified 35 children for inclusion. After the first OPT, a second OPT with a different BL was performed in case of a positive result of the first one. In 12 cases (34.2%), the OPT elicited a reaction. In eight cases the allergy was to penicillin and in two cases to cephalosporins (cefixim). Cross-reactivity was noted in two cases. Conclusion: An OPT to BL indicated in the first instance in non-severe reaction in children will allow a rapid diagnosis in case of suspicion of HS to BL.

Placebo-Controlled Histamine Challenge Disproves Suspicion of Histamine Intolerance.

BACKGROUND: Histamine intolerance (HIT) is frequently diagnosed in patients with polysymptomatic otherwise unexplained symptoms. OBJECTIVES: To exclude HIT by a single-blind placebo-controlled histamine challenge (SBPCHC), to study clinical features of patients with positive challenge, and to examine the predictability of HIT by biomarkers. METHODS: SBPCHC was performed in 59 patients with suspected HIT. History and clinical data, including serum diamine oxidase (DAO) and histamine skin test wheal size of patients with positive versus negative SBPCHC, were compared. RESULTS: Patients were predominantly middle-aged women (84.7%). Three-quarters reported improvement but never resolution of symptoms during a histamine-low diet. Histamine provocation was safe; only 1 patient was treated with antihistamines. Thirty-seven patients (62.7%) displayed symptoms to placebo. HIT was excluded in 50 patients (84.7%). Objective symptoms occurred in 4 of 59 cases (6.8%) after histamine but not after placebo challenge. These were diagnosed with "plausible HIT" because reactions occurring by chance could not be excluded. Another 5 patients (8.5%) were diagnosed with "possible HIT" after case-dependent detailed analysis. Patients with plausible/possible HIT had reported more gastrointestinal symptoms (P = .01), but comparable diet response and equal histamine skin prick test wheal sizes to those without HIT. Serum DAO activity tended to be lower in patients with HIT (P = .08), but was highly variable in those without, limiting its value as a biomarker. CONCLUSIONS: SBPCHC disproves HIT in the majority of patients. Placebo-controlled challenges are needed as placebo reactions were frequent. Gastrointestinal symptoms after food intake and reduced DAO levels are markers for HIT; however, specificity is not sufficient enough for making the diagnosis.