Feline panleukopenia virus (FPV) PCR in cats

What it shows

PCR detects the DNA of FPV in a sample. Faeces, whole blood, bone marrow and tissue are possible samples; faeces are used most often. PCR is more sensitive than the quick antigen tests run in the clinic, so ABCD advises a PCR when a cat with suspected panleukopenia has a negative in-clinic test.

PCR finds the virus’s genetic material, not the illness itself.

Higher than reference — what it may be a sign of

For PCR, “higher than reference” means the virus was detected. Possible explanations:

• Panleukopenia — in a cat with typical signs and a low white blood cell count, a positive result supports the diagnosis.
• Recent vaccination — modified live vaccine virus is shed in faeces. Faecal antigen tests and faecal PCR can be positive for at least 4 weeks after such a vaccine. Vaccination within 14 days may also give a false positive in-clinic antigen test. That is why the vet asks for the date of the last vaccine.
• Healthy shedders — healthy cats have been described whose faecal PCR stayed positive over weeks. Kittens infected in the womb may shed virus for a long time. Persistent infection itself is rare.
• Canine parvovirus variants — CPV-2a, 2b and 2c can infect cats and cause panleukopenia, and circulating canine strains can cause clinically significant disease in cats.

Lower than reference

“Not detected” is the expected result in a healthy cat. It does not exclude infection in every case: virus may be present below the test’s detection limit. Viral load can be low and shedding in faeces can be intermittent — this is also why a negative in-clinic test is followed by PCR. The Merck manual advises confirming a negative result in a kitten with typical signs by testing again. The vet decides whether and when to repeat the test.

Look at together with

• White blood cells — FPV lowers them; in severely affected cats, especially kittens, counts as low as 0.05–3 × 10⁹/L have been reported.
• Neutrophils and lymphocytes — a blood smear may show a deep fall in both, with neutrophils falling before lymphocytes.
• Platelets — a low count is sometimes reported.
• In-clinic faecal antigen test — a positive result in a sick cat supports the diagnosis; a negative one leads to PCR.
• Vaccination record — the type and date of the last vaccine.

Units and conversion

PCR has no units: the form shows whether FPV DNA was “detected” or “not detected” (sometimes “positive” / “negative”) in the sample sent, most often faeces. Some forms also print a Ct value; what it means is explained in the article on feline herpesvirus PCR. In the app the result is stored as text, as printed on the form.

Reference range

The reference range is on your lab’s form; for this PCR it is usually “not detected”. A positive result is read together with the signs, the white blood cell count and the date of the last vaccine. A negative result in a cat with typical signs does not close the question. The result helps the vet choose the next steps.

Cats and dogs

Sources

1. ABCD (European Advisory Board on Cat Diseases) — Guideline for feline panleukopenia
2. DeTar L. Feline Panleukopenia. Merck Veterinary Manual, professional version
3. Cornell Feline Health Center — Feline Panleukopenia Virus
4. Merck Veterinary Manual — Canine Parvovirus Infection (Parvoviral Enteritis in Dogs)
5. Cornell University Animal Health Diagnostic Center — Interpretation of PCR results
6. UC Davis Real-time PCR Research and Diagnostics Core Facility — Diagnostic FAQs