There is a test which will look for the presence of coronavirus
antibodies in your cat’s blood. If your cat has been exposed to a
coronavirus, ANY coronavirus, its immune system will build up
antibodies to it, and the titer tests for the level of those antibodies
in the blood. But it does not distinguish between antibodies made
specifically against FIP, or FECV, or any other coronavirus. A
positive titer means only that your cat has created antibodies
(therefore been exposed to) SOME form of coronavirus. The higher the
titer, the more antibodies the cat has created.
As if there were not enough problems with the
coronavirus test, there
is no uniformity between different labs. One cannot compare results
from one lab to another. Some labs just specify positive or negative if
the results are above or below a given titer (often these labs do not
even specify the titer). There are no standards for setting up a lab,
there is no regulatory body that oversees them, and no requirement for
validation of test results. It is also possible for a cat which has
received the vaccine (more below) to have enough antibodies to appear
on the titer test. To top it all off, false positives occur in up to
30% of the tests. In sum: DO NOT PLACE MUCH CREDENCE IN THE TITER TEST,
AND UNDER NO CIRCUMSTANCES SHOULD A CAT BE EUTHANIZED BASED SOLELY ON
THE RESULTS OF THE TITER TEST.
There are some clinical indicators which your vet may discuss with you
if s/he suspects that a cat has FIP, particularly if it is showing
likely symptoms. Some blood tests can help your vet pinpoint FIP as a
cause for your cat’s condition, this includes looking for a high amount
of gamma globulin proteins and a low amount of albumin proteins in the
blood.
There has also been talk of a polymerase chain reaction (PCR) test, in
the hopes that it can tell the difference between FIP and other
coronaviruses. Significant scientific studies have yet to be concluded
on this method. However, given that the most common way of a cat
coming down with FIP is via the mutation of FECV, this test may have
little or no value in the great majority of cases.