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Diagnosing immediate drug hypersensitivity reactions (IDHRs) can pose a significant challenge and there is an urgent need for safe and reliable tests. Evidence has emerged that the basophil activation test (BAT), an in vitro assay that mirrors the in vivo response, can be a complementary test for many drugs. In this position paper, members of Task Force (TF) "Basophil activation test in the evaluation of Drug Hypersensitivity Reactions" from the European Academy of Allergy and Clinical Immunology (EAACI) present the data from a survey about the use and utility of BAT in IDHRs in Europe. The survey results indicate that there is a great interest for using BAT especially for diagnosing IDHRs. However, there are still main needs, mainly in the standardization of the protocols. Subsequently consensus‐based recommendations were formulated for: (i) Technical aspects of BAT in IDHRs including type of sample, management of drugs, flow cytometry protocols, interpretation of the results; and (ii) Drug‐specific aspects that should be taken into account when performing BAT in relation to betalactams, neuromuscular blocking agents, fluoroquinolones, chlorhexidine, opioids, radio contrast media, chemotherapeutics, biological agents, nonsteroidal anti‐inflammatory drugs, COVID vaccine, and excipients. Moreover, aspects in the evaluation of pediatric population have also been considered. All this indicates that BAT offers the clinician and laboratory a complementary tool for a safe diagnostic for IDHRs, although its place in the diagnostic algorithm depends on the drug class and patient population (phenotype, geography, and age). The standardization of BAT is important for generalizing this method beyond the individual laboratory. [ABSTRACT FROM AUTHOR]

Background: Vaccination of the population is required to combat the COVID‐19 pandemic. Allergy testing could reduce anxiety towards COVID‐19 vaccination and thereby may increase vaccination rate, however, its effectiveness remains unclear. Methods: One hundred and thirty prospective real‐life patients in need of but not daring to get vaccinated asked for allergy workup for COVID‐19 vaccine hypersensitivity in 2021/2022. Characterization of patients, identification of anxieties, decrease of patient's anxiety levels, overall vaccination rate and adverse reactions after vaccination were assessed. Results: Tested patients were characterized by being female (91.5%) and having a high rate of previous allergies (e.g. to food 55.4%, drugs 54.6%, or previous vaccinations 50%) and dermatological disease (29.2%) but not always had medical contraindications for COVID‐19 vaccination. Sixty one patients (49.6%) were highly concerned (4‐6, Likert scale 0‐6) about vaccination and 47 (37.6%) expressed resolving thoughts about vaccinaion anaphylaxis (3‐6, Likert scale 0‐6). However only 35 patients (28.5%) were scared of getting COVID‐19 within 2 months (4–6, Likert scale 0–6) and only 11 (9%) patients had high expectations of getting COVID‐19 (4–6, Likert scale 0–6). Allergy testing significantly (p < 0.01 to p < 0.05 respectively) reduced the median anxiety of allergic symptoms following vaccination: dyspnoea (4.2–3.1), to faint (3.7–2.7), long‐term consequences (3.6–2.2), pruritus (3.4–2.6), skin rash (3.3–2.6) and death (3.2–2.6). After allergy testing, most patients (108/122, 88.5%) let themselves be vaccinated within 60 days. Revaccinated patients with previous symptoms experienced a reduction of symptoms (p < 0.05) upon revaccination. Conclusions: Patients not daring to get vaccinated have more anxiety towards vaccination than to acquire COVID‐19. For those, allergy testing excludes vaccine allergy, and is a tool to increase vaccination willingness and thereby helps to combat vaccination hesitancy. [ABSTRACT FROM AUTHOR]

Background: Cutaneous lesions of mastocytosis (CLM) are often subtle and may require biopsy. However, dermatohistopathological criteria for CLM remain undefined. Objectives: To establish criteria for CLM by validating histological and molecular parameters. Methods: In skin samples from Caucasian patients with CLM and controls (atopic dermatitis, chronic urticaria, pruritus, tissue from tumor safety margin excisions), mast cell (MC) numbers, size, shape, distribution, immunostainability with a large panel of markers, pigmentation and presence of KIT D816V mutation were analysed. Results: Forty‐seven CLM patients (32 maculopapular cutaneous mastocytosis (MPCM), 15 mastocytomas) and 36 controls were included. Mastocytomas were easily identified by densely packed cuboidal MCs. In MPCM, skin MC density in CD117 stains was higher in CLM patients than in controls (P < 0.0001) and values correlated closely (r = 0.65, P < 0.0001) to results in tryptase stains. The optimized upper dermis cut‐off number of 62 MC/mm2 had a sensitivity and specificity of 92% in both stainings, corresponding to approximately 12 MC/high power field (HPF). MC size was larger in MPCM than in controls (P = 0.01). Interstitial (= not perivascular or periadnexal) MCs and stronger basal pigmentation of the epidermis were indicative of MPCM (P < 0.0001 each) and clusters of >3 nucleated MC/HPF exclusively found in MCPM. Surface markers CD2, CD25 and CD30 stained T‐lymphocytes, but only negligibly CLM MC. The KIT D816V mutation in formalin fixed paraffin embedded (FFPE) skin was evaluable in 87.5% of MCPM patients and had both 100% sensitivity and specificity. Conclusions: MPCM can be predicted by major and minor criteria combined in a scoring model. Presence of D816V mutation in FFPE skin and MC density > 27/HPF are >95%‐specific major criteria for MPCM. MC densities 12/HPF, interstitial MC, clusters and basal pigmentation are minor criteria. [ABSTRACT FROM AUTHOR]