FIP diagnostic is challenging as clinical signs are diverse (depending on the involved organs), and therefore not specific to FIP and can mimic many other medical conditions.  On the other hand the accuracy of FIP diagnosis is highly important as being almost a 100% fatal disease which mostly ends with euthanasian of the FIP infected cat. 

Unfortunately, there isn’t a one simple blood test to confirm a diagnosis of FIP, rather than multi-stages and tools combinations in order to get to the most accurate diagnosis possible.