Antech Diagnostics presently offers two serologic tests and one molecular biology-based, polymerase chain reaction test to aid in the diagnosis of feline infectious peritonitis (FIP):

• Feline coronavirus IFA (FCV-IFA) is a serologic test detecting antibodies to coronaviruses. This test is sensitive but certainly not specific for FIP (see "New Coronavirus Exposure Titer").
  
• FIP Polymerase Chain Reaction (FIP-PCR) detects the expression of the 7b gene, and measures antigen. The expression of this gene is specific for pathogenic coronavirus (FIPV). It is specific and works well on effusions, but lacks sensitivity when performed on whole blood.
  
• FIP-Specific ELISA (FIPSE) is a serologic test which detects antibodies against the protein that is encoded for by the 7b gene (i.e. the 7b protein). By focusing on the 7b protein this test has markedly enhanced specificity for FIP when compared to the FCV-IFA. As with all serology, it must be interpreted in conjunction with patient history and clinical signs.

Following the introduction of the FIPSE, Antech Diagnostics embarked on an additional six-month prospective study of 28 cats with positive FIPSE titers. All cats were FeLV/FIV negative. Each cat was titered monthly for FIPSE. Routine bloodwork was evaluated initially and at the onset of any signs of illness. FIP was confirmed by histopathology with or without PCR on all cats that died during the study period. While the study is ongoing, the following observations have been made:

• Monthly titers often fluctuated.
  
• 57% of cats became negative by FIPSE during the study. Of cats with low positive titers (1:40 and 1:80), 75% became FIPSE negative. Of cats with higher titers (1:160 and 1:320), 14% became negative. All of these seronegative cats remain clinically healthy.
  
• 11% of cats in the study died of FIP. Of cats with low positive titers (1:40 and 1:80), 5% died. Of cats with higher titers (1:160 and 1:320), 25% died.
  
• Three cats died of FIP (one non-effusive, two effusive). These cats entered the study without clinical signs, but with FIPSE titers of 1:160, 1:80, and 1:320. When they died, their titers were 1:160, 1:80 and 1:80, respectively. All had hyperglobulinemia, hypoalbuminemia, and anemia. These laboratory findings were present weeks before the onset of clinical signs in two of the cases.
  
• 32% of cats remain seropositive and are all healthy to date.
  
• FIPSE titers indicates exposure to FIPV, but seropositivity does not necessarily predict disease.

Selection of the appropriate test for each case is dependent on the clinical situation. In addition to your standard clinical database, the following recommendations can be made:

* For cats with effusive disease, perform PCR testing on the effusion. Be sure to submit a fresh specimen in a LTT, which has been refrigerated and sent on an ice pack. For optimal recovery of the antigen (RNA), this should not be added on to a specimen previously submitted for fluid analysis. A FIPSE run on effusive cases may provide you with quicker turn around time, but please note that a small percentage of cats with effusive FIP may be negative on the FIPSE test just as they may be negative on the FCV-IFA.

* For cats that have non-effusive disease and are FIP suspects, submit FIPSE (serum, RTT or STT only, no LTT) to document exposure to FIPV. If the cat has granulomatous disease for which you are submitting biopsies, consider running PCR on fresh tissue samples. These should be submitted in a small amount of saline in a plain red top tube and kept cold. (LTT should not be used for FIPSE, as it may interfere with the reaction.)

* For cats with known exposure to FIP, consider running FIPSE (serum only) at least 3 weeks after the last known contact. If the test is positive, it documents immunologic response, but clinical outcome cannot be predicted by a single positive test. These cats should be followed over time, both clinically and with laboratory data.

* For healthy new cats coming into a household, consider running both the FIPSE to document prior exposure to FIP and the Exposure Titer #5342 to document exposure to enteric coronavirus. While a cat may be negative on the FIPSE, if it has been infected with enteric coronavirus it is still potentially at risk for viral mutation and developing FIP. Therefore, a coronavirus positive cat entering a multicat household may create risk for all felines in the household.

* Vaccinating cats for FIP may produce a positive FCV-IFA titer, but vaccination will not affect the FIPSE.