Clinical efficiency of in vitro and in vivo tests for allergic diseases

Specific serum IgE determination is widely used in the diagnosis of IgE-mediated allergic diseases but the relative merits of in vitro measurement of IgE antibody in comparison to in vivo skin tests are still debated.

The aim of this study was to investigate the clinical efficiency of a "second generation" technique for in vitro analysis of IgE antibody (Pharmacia CAP System).

Eighty-six patients with suspected inhalant and/or food allergies and 20 asymptomatic subjects for a total of 655 tests were evaluated. Sera with divergent results between in vitro and in vivo techniques were further analyzed by using ImmunoCAP inhibition and immunoblotting. For the calculation of sensitivity and specificity of both in vitro and in vivo tests we considered as true value (reference value) either the concordant results or, in case of discordance, the datum confirmed by ImmunoCAP inhibition or immunoblot (ie, vitro positive, vivo negative, ImmunoCAP inhibition positive; true result: positive).

The obtained results demonstrate that the in vitro results correlate well in terms of specificity and sensitivity to this new reference standard. In particular a higher specificity for Pharmacia CAP System in comparison to in vivo skin prick test for grass pollens and a better sensitivity for mites and cat allergens were found.

Our results suggest that the in vitro "second generation" testing provides reliable results in all clinical situations.