Reduction in false antigenemia in the second generation Histoplasma antigen assay.

We have previously reported false Histoplasma antigenemia in solid organ transplant patients who received rabbit antithymocyte globulin (ATG). False antigenemia was caused by human anti-rabbit antibody, produced in response to ATG administration. Those specimens were obtained through a research study to assess the development of anti-rabbit antibodies following ATG administration. Here we compare the likelihood of false antigenemia between the original and second generation assays in clinical specimens obtained specifically for the diagnosis of histoplasmosis. Of 12 serum specimens that were falsely positive in the original assay, four (33%) remained positive in the second generation assay. The sensitivity was 98% in urine was and 80% in serum in patients with AIDS complicated by disseminated histoplasmosis. False-positive results were not observed in serum or urine from healthy subjects. Thus, the second generation assay is less susceptible to false antigenemia caused by anti-rabbit antibodies.