Histoplasma antigen test results are influenced by the urine collection method in dogs

A commercially available Histoplasma urine antigen enzyme immunoassay (MV antigen EIA; MiraVista Diagnostics) is widely used to support the diagnosis of histoplasmosis in dogs; however, a standardized urine collection technique does not exist. The objective was to evaluate agreement between 3 urine collection techniques (free catch [FC], cystocentesis [cysto], and iatrogenically hospital-contaminated cystocentesis [contam]) using the MV antigen EIA in dogs and to determine associated false-positive rates (FPRs).

Participants were 30 dogs suspected of histoplasmosis and 30 temporally matched, healthy controls. In this 12-month prospective study (December 2023 to 2024), 3 urine samples (FC, cysto, and contam) were collected within 24 hours from each dog. Agreement between methods was assessed using the McNemar test and Cohen κ coefficients. False-positive rates were calculated using clinical diagnosis as the reference standard.

3 clinically ill dogs were definitively diagnosed with histoplasmosis. Agreement was substantial between cysto and contam samples (κ = 0.68; 95% CI, 0.39 to 0.97) and moderate between cysto and FC (κ = 0.45; 95% CI, 0.07 to 0.82) and FC and contam samples (κ = 0.42; 95% CI, 0.10 to 0.75). The overall FPR was 16% (9 of 57; 95% CI, 6 to 25%). The cysto samples had the lowest FPR (4% [2 of 57]; 95% CI, 1 to 12%), followed by FC (7% [4 of 57]; 95% CI, 3 to 17%) and contam (11% [6 of 57]; 95% CI, 5 to 21%).

While all collection techniques demonstrated reasonable agreement, FC and contam samples were more prone to false positives.

Clinicians should confirm contam low-level positive results with sterile cysto to improve diagnostic accuracy and clinical decision-making for histoplasmosis in dogs.