PCR is Fluid Test. This is the only real Test If it is FIP or Not, when it is wet FIP.
Rivalta test In a 2012 study of almost 500 cats with effusions (not only FIP, but also other diagnoses), it was found that a negative Rivalta test could rule out FIP in 93% of cases. If the test was positive, 58% of the cases were FIP. In most FIP cats, this test is positive and is usually yellowish and stringy. With FIP, the effusion often contains a lot of protein (exudate) but few cells. However, false positive results can occur in cats with bacterial peritonitis. However, these effusions are usually easy to distinguish (by macroscopic examination, cytology, bacteriological examination). Some cats with malignant lymphoma also react positively to the Rivalta test, but many of them can be diagnosed in the cytological examination by the detection of tumor cells. RealPCR examination Examination at Idexx using FIP Virus Real PCR. The polymerase chain reaction (PCR) enables the detection of even the smallest amounts of virus in a tissue or fluid sample. When examining blood, the sensitivity is around 15 percent and when examining mononuclear cells it is 29%. The specificity is 86–100%. The detection of virus RNA does not allow a distinction between harmless and mutated coronaviruses. In contrast, RT ‐ PCR from effusion fluid has high sensitivity and specificity (> 90%). Depending on the clinical manifestation, peritoneal and pleural fluid, liquor, tissue aspirates or biopsy samples are suitable as material. Biotyping from faecal samples is not possible or useful. The detection in the feces is only used to detect coronavirus shedding, it is unsuitable for diagnosing the disease.