Enyzme immunoassay compared to immunodiffusion complement-fixation to assess the IgG serological response in coccidioidomycosis

Enzyme immunoassay (EIA) is often the initial test performed for diagnosing coccidioidomycosis by serology. When EIA immunoglobulin G (IgG) optical density (OD) positive results were compared to immunodiffusion complement-fixation (IDCF) titer among 339 unique patient samples, there was only moderate correlation (R2=0.5345; P <0.001). In 68 cases (20.1%), the EIA IgG was positive when the IDCF result was negative. When the medical records of 22 patients at one site were reviewed, only 14 (63.6%) with positive EIA IgG tests were associated with clinically active coccidioidomycosis. These results support not using EIA IgG OD as a substitute for CF titer and that an isolated positive EIA IgG may be falsely positive.