Evaluation of assays of serum IgG subclasses and IgG antigen-specific antibodies in the investigation of recurrent infection

Patients who have recurrent infections require laboratory investigation for possible underlying immunodeficiency. We retrospectively evaluated the use fulness of two relevant assays (serum IgG subclass concentration and levels of IgG antigen-specific antibodies to a panel of relevant carbobydrate and protein antigens) in the management of patients referred to a regional cli nical immunology service over a 3-year period. Of 97 patients for whom both assays were performed, five (5.2%) had a low result for IgG subclasses but this did not influence the management of any patient; 51 patients (53%) ha d a low result for antigen-specific antibodies and this influenced manageme nt in 43 cases. We conclude that knowledge of the serum IgG subclass concen trations is of dubious relevance and this calls into question whether the a ssay should continue to be offered. This regional service has ceased to per form the assay routinely in such patients. Our findings require confirmatio n by a larger multicentre study that should assess the clinical outcome of any changes in practice.