Histoplasma Antigen Clearance during Treatment of Histoplasmosis in Patients with AIDS Determined by a Quantitative Antigen Enzyme Immunoassay

Clearance of Histoplasma antigen has been used as a marker for response to treatment of progressive disseminated histoplasmosis (PDH) in patients with AIDS. Advancements in Histoplasma antigen detection permit accurate quantification of antigen concentration. We compared the clearance of antigenemia and antigenuria during effective treatment of PDH. Urine and serum specimens were serially collected from patients with AIDS who were successfully treated for PDH as part of two prospective clinical trials. Samples were stored frozen until they were tested in the quantitative Histoplasma antigen enzyme immunoassay. The kinetics of antigen clearance during the first 12 weeks of therapy were assessed in urine and serum during treatment with liposomal or deoxycholate amphotericin B followed by itraconazole and, in a separate analysis, in patients receiving only itraconazole. Latent class growth analysis was performed to define patterns of antigen clearance over time. In patients receiving amphotericin B, antigen levels declined the most during the first 2 weeks of treatment and antigenemia decreased more rapidly than antigenuria (5.90 ng/ml per week versus 4.21 ng/ml per week, respectively; P = 0.09). Mean reductions of antigen levels from baseline at weeks 2 and 12 were greater in sera than in urine: 11.26 ng/ml versus 7.65 ng/ml (P = 0.0948) and 18.52 ng/ml versus 14.64 ng/ml (P = 0.0440), respectively. In patients who received itraconazole alone, most of the decline in antigenuria occurred later during treatment and was overall slower than that seen with amphotericin B (P < 0.0001). Results of latent class growth modeling showed two distinct trajectories for each parameter. With effective therapy, Histoplasma antigenemia decreases more rapidly than antigenuria, providing a more sensitive early laboratory marker for response to treatment. Antigenuria declines earlier with amphotericin B than with itraconazole.