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

Confirm low-level positive Histoplasma antigen results from free-catch urine with sterile cystocentesis to reduce false positives.

This prospective 12-month study (December 2023–2024) evaluated agreement among three urine collection methods—free catch (FC), cystocentesis (cysto), and iatrogenically contaminated cystocentesis (contam)—for the MiraVista Histoplasma urine antigen enzyme immunoassay (MV antigen EIA) in dogs. Thirty dogs suspected of histoplasmosis and 30 healthy controls were enrolled, with three urine samples collected from each dog within 24 hours. Only 3 clinically ill dogs received a definitive histoplasmosis diagnosis. Agreement between cysto and contam samples was substantial (κ = 0.68), while agreement between cysto and FC (κ = 0.45) and FC and contam (κ = 0.42) was only moderate. The overall false-positive rate (FPR) was 16% (9/57). Cystocentesis yielded the lowest FPR at 4% (2/57), followed by free catch at 7% (4/57) and contaminated cystocentesis at 11% (6/57). These findings highlight that environmental or iatrogenic contamination during urine collection can meaningfully elevate false-positive rates with this assay. Clinicians relying on free catch or potentially contaminated samples risk initiating unnecessary antifungal therapy in non-infected patients. The authors recommend confirming low-level positive results obtained from non-sterile collection methods with a sterile cystocentesis sample to improve diagnostic accuracy. This study underscores the importance of standardizing urine collection protocols when using the MV antigen EIA to support histoplasmosis diagnosis in canine patients.

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