Pretreatment Histoplasma capsulatum urine enzymatic immunoassay concentrations do not correlate with outcome but may be influenced by renal function in cats with histoplasmosis.

Objectives: The objective of this study was to determine if urine Histoplasma antigen (HAg) enzyme immunoassay (EIA) concentrations at the time of diagnosis and prior to the administration of antifungal agents are predictive of outcome for cats infected with Histoplasma capsulatum and to determine if compromised renal function affects urine HAg EIA measurements.

Methods: Medical records at four institutions were searched to identify cats diagnosed with histoplasmosis between April 2012 and December 2015. Pretreatment urine Histoplasma EIA values were recorded, along with patient signalment, serum creatinine concentration, urine specific gravity, site(s) of infection and survival data.

Results: Pretreatment urine HAg EIA measurements were available for 50 cats, and ranged from 0-19.1 ng/ml (median 6.3 ng/ml). Thirty-five cats were alive at day 180, 12 had died or were euthanized (median survival time 24 days; range 2-124 days) and three were lost to follow-up. The median urine HAg EIA at the time of diagnosis for cats alive at 6 months was 5 ng/ml (range 0-19.1); this was similar to findings for the non-survivors (median 7.29 ng/ml; range 0.78-19.1; P = 0.54). Surviving cats were significantly younger (mean age 6.9 years) than non-survivors (mean age 9.9 years; P = 0.03) but median body weights (3.8 kg vs 3.6 kg) and rates of pulmonary involvement (22/35 vs 9/12) were similar for the two groups. Median urine HAg EIA concentration was lower in cats with evidence of renal compromise than cats with acceptable renal function (0.54 ng/ml vs 7.2 ng/ml; P <0.013).

Conclusions And Relevance: Urine HAg EIA concentrations at the time of diagnosis are not predictive of outcome in cats with histoplasmosis and should not be used as a prognostic indicator in this species. Renal function may influence urine HAg EIA concentrations in cats; further investigation is needed to see if concurrent kidney disease impacts test sensitivity.