Peer-reviewed veterinary case report
Blood PCR test often misses histoplasmosis in cats confirmed by other
By Sebastian, Jamie F et al.·Published in Journal of the American Veterinary Medical Association·2024·Kansas State University·View original on PubMed →
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Original publication title: A commercial whole blood polymerase chain reaction assay failed to diagnose histoplasmosis in cats confirmed by cytology or urine antigen detection.
- Species:
- cat
Plain-English summary
Ten cats suspected of having histoplasmosis (a fungal infection) were tested using a blood test that was found to be ineffective. None of the cats tested positive for histoplasmosis using this blood test, even though some had confirmed cases through other methods like urine tests or cytology. In contrast, a different test that looked for antibodies against the fungus was much more reliable, correctly identifying most cases. This study suggests that the blood test should not be used for diagnosing histoplasmosis in cats, and better testing methods are needed.
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Abstract
OBJECTIVE: To determine the sensitivity and specificity of a commercial whole blood real-time PCR assay (RT-PCR) for the diagnosis of histoplasmosis when compared to direct organism identification and/or urine antigen quantification by enzyme immunoassay (UA-EIA). A secondary objective was to compare the sensitivity and specificity of RT-PCR to anti-Histoplasma immunoglobulin G antibody detection by enzyme immunoassay (IgG-EIA) and IgG-EIA to UA-EIA. ANIMALS: Cats presented to the Kansas State University Veterinary Health Center from February through September of 2023 in which histoplasmosis was diagnosed or suspected. METHODS: From February through September of 2023, cats were tested by RT-PCR, IgG-EIA, and UA-EIA if histoplasmosis was diagnosed cytologically or was a differential diagnosis for the presenting clinical signs. Cats were excluded if all 3 tests were not submitted or if the diagnosis of histoplasmosis could not be excluded despite a negative UA-EIA result. Cats with cytologically or histologically confirmed histoplasmosis were designated as proven histoplasmosis cases, and cats with a positive UA-EIA result without cytological or histological confirmation were designated as probable histoplasmosis cases. RESULTS: 10 cats were diagnosed with either proven (n = 6) or probable (4) histoplasmosis, and 10 cats were considered true negatives. Whole blood RT-PCR results were negative in all 20 cats (sensitivity, 0%; 95% CI, 0% to 30.85%). The IgG-EIA was 90% sensitive (95% CI, 55.50% to 99.75%) and 70% specific (95% CI, 34.75% to 93.33%). The UA-EIA results were positive in all cats with proven histoplasmosis. CLINICAL RELEVANCE: This commercial RT-PCR is insensitive when used on whole blood collected in EDTA and should not be used to diagnose feline histoplasmosis. Further studies are required to determine whether alternate RT-PCR protocols for EDTA-collected whole blood could be useful for diagnosing histoplasmosis in cats.
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Search related cases →Original publication on PubMed: https://pubmed.ncbi.nlm.nih.gov/38848745/