IgM and IgG antibodies to Coccidioides antigen usually appear during the first month of infection, decline over the next 3-6 months but remain detectable for approximately 18-24 months in some cases with self-limited illnesses. Antibodies may persist in patients with chronic pulmonary complications or progressive extrapulmonary (disseminated) coccidioidomycosis. Antibodies may be falsely-negative in some progressive or chronic cases. Follow-up testing maybe considered at weeks 2 – 4 to determine if antibody levels are increasing especially in patients with low positive (10 EU – 20 EU) or intermediate results. Increase in antibody concentration would suggest recent infection. Antibodies may also be detected in healthy subjects who are asymptomatic as a result of sub-clinical infection within the last 18 – 36 months.