Research overview: the diagnostic challenge of FIP

FIP has long been notoriously difficult to diagnose definitively before death because no single non-invasive test is both highly sensitive and specific, and because antibody to feline coronavirus is common in healthy cats. Clinicians integrate signalment, clinical signs, effusion analysis, blood changes such as elevated globulins and altered albumin:globulin ratio, imaging, and supportive tests, with immunostaining of affected tissue providing confirmation. This overview compiles the diagnostic literature rather than one citation, describing why coronavirus serology alone cannot diagnose FIP, how effusion characteristics and tissue immunohistochemistry strengthen confidence, and why accurate diagnosis became even more important once effective antiviral treatment emerged, since the decision to commit to a long, costly therapeutic course depends on it.