Importance of Specific IgE/Total IgE Ratio in Disambiguating Amoxicillin Allergy Diagnosis in a Real-Life Setting

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Authors: Marcello Albanesi, Alessandro Sinisi, Flavia Frisenda, Danilo Di Bona, Maria Filomena Caiaffa and Luigi Macchia
Date: Sept. 2018
From: International Archives of Allergy and Immunology(Vol. 177, Issue 2)
Publisher: S. Karger AG
Document Type: Letter to the editor
Length: 1,502 words

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Dear Editor,

Allergic reaction to [beta]-lactams antibiotics is the most frequent cause of Adverse Drug Reaction (ADR) mediated by immunological mechanisms [1]. In clinical practice, the evaluation of [beta]-lactam-specific IgE levels is instrumental in the establishment of the diagnosis of ADR [2]. Drug-specific IgE titres rise 3-4 weeks upon exposure and decline over time [3].

Assessment of circulating drug-specific IgE is often done using the RAST-CAP system. The specificity of this test was assessed to range between 83.3 and 100%, with a 0.35 kU/L threshold, but the sensitivity was estimated to range only from 12.5 to 25% [4]. However, a 0.1 kU/L threshold is currently considered acceptable, increasing the sensitivity but possibly reducing the specificity [5].

The test-positive predictive value might also be influenced by the total serum IgE. Indeed, 2 different pools of IgE molecules exist: (i) IgE molecules bound on the mast-cell and basophil surface via the interaction with the high affinity receptor FceRI and (ii) the unbound IgE molecules that circulate freely in plasma [6]. It was recently proposed that the ratio [beta]-lactam-specific IgE/total IgE might be an additional parameter to consider in the ADR diagnostic process [7]. In particular, an elevated drug-specific IgE/total IgE ratio might reflect high levels of drug-specific IgE on mast-cells and basophils, thereby increasing the probability of adverse reaction upon drug administration. Thus, the authors propose the use of a 0.002 threshold for the ratio drug-specific IgE/total IgE. A positive predictive value of 95% is achieved if the ratio is [greater than or equal to] 0.002, whereas it diminishes significantly if the ratio is <0.002 [7].

Here we describe 6 cases of suspected ADR to amoxicillin (AMX). We used the 0.002 amoxicilloyl-specific IgE/total IgE ratio to clarify the clinical diagnosis in a real-life setting.

The patients (1 men and 5 women; mean of age 38.6 [+ or -] 16.3; all from Southern Italy) were referred to our Clinic for a suspected (although ambiguous) immediate ADR to AMX. Five patients had been treated with AMX alone and one with AMX-Clavulanic Acid (CLV). Five out of 6 had experienced the adverse reaction more than 6 months before the clinical assessment and no other concomitant medications were given (Table 1).

In all patients, the amoxicilloyl-specific IgE levels (CAP System) were...

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Source Citation
Albanesi, Marcello, et al. "Importance of Specific IgE/Total IgE Ratio in Disambiguating Amoxicillin Allergy Diagnosis in a Real-Life Setting." International Archives of Allergy and Immunology, vol. 177, no. 2, Sept. 2018, pp. 167+. Accessed 1 Dec. 2021.

Gale Document Number: GALE|A602716901