Background: In vivo allergy tests and the detection of drug-specific antibodies are widely used in the diagnosis of β-lactam induced immediate-type hypersensitivity reactions. The diagnostic performance of immunoenzymatic tests for the demonstration of serum-specific IgE (IgEs) antibodies is influenced by total IgE values (IgEt). The aim of this study was to investigate whether the result obtained by radioimmunoassays (RIA) for β-lactams IgEs antibodies is correlated to IgEt.
Methods: 68 paired in vivo and in vitro tests were performed for the culprit drugs in 49 patients with suspected previous hypersensitivity reactions to β-lactams. 14 controls who tolerated the tested antibiotics were similarly investigated. The dosing of IgEt was performed using the Immulite Immunoassay (Siemens). We detected IgEs using a sandwich-type RIA with sepharose as solid phase (Pathologie Cellulaire et Moléculaire en Nutrition, France) and anti-IgEs I(125)-labelled antibodies (Immunotech, Czech Republic).
Results: RIA-IgEs sensitivity was 56.52% in patients with IgEt < 120 IU/mL and 90.90% in patients with IgEt > 120 IU/mL (p = 0.0052). All patients with IgEt > 500 IU/mL had positive RIA results. RIA-IgEs specificity was 90.90% for IgEt < 120 IU/mL and 66.66% for IgEt > 120 IU/mL. The linear equation that fits the relation between IgEt and IgEs is: IgEs = (IgEt + 81.644)/137.94, with a correlation coefficient of 0.4.
Conclusions: Serum total IgE alter the diagnostic performance of radioimmunoassays for β-lactam specific antibody dosing. Assays for the detection of both IgEt and IgEs need to be performed for each individual investigated, retrospectively, to confirm clinical immediate-type hypersensitivity reactions.