As a general rule, fecal testing (parvovirus antigen or PCR) is preferred over serological tests for confirming a diagnosis of canine parvovirus.

The fecal parvoviral antigen test is used in dogs showing clinical signs of parvovirus gastroenteritis. The test is very specific for parvovirus infection, but is not very sensitive (many false negative results, so that a negative test result does not rule out parvovirus infection). Parvovirus antigen can be detected in feces for only a short period after infection (experimentally from days 5-8 post-infection).

False negative results can result from:

• Dogs tested too early (may not yet be shedding virus);
• Dogs tested too late (no longer shedding virus or all virus in feces is bound by antibodies and thus not detected).

False positives can result from:

• Recent MLV vaccination (in the last 5-15 days);
• Laboratory error from insufficient washing during the test, especially if the stool is very mucoid.

The test requires 1-2g of feces in a plain RTT sent to the lab on ice. The test code is T695. The test is run daily, except Sunday.

The parvovirus PCR test has been shown to be much more sensitive for detecting canine parvovirus in feces than the fecal antigen test. Dogs experimentally exposed to parvovirus had positive fecal PCR tests from days 3–14 after exposure. The parvovirus PCR test will often confirm the presence of fecal parvovirus DNA even when the parvoviral antigen test is negative. Recent modified parvovirus vaccination (within 14 days) may cause false positive results.

The test code for the fecal parvovirus PCR test is S8710. The test requires 1-2g of fresh feces in a plain RTT sent to the lab on ice (if left out for a few hours, may cause false negative results). The turn around time is 5 days. While waiting for test results, the case should be managed as if the dog had parvoviral gastroenteritis.

Evaluation of serum parvovirus antibody titers is often less helpful in confirming a diagnosis of parvoviral gastroenteritis, because vaccinated dogs or puppies with residual passive antibody obtained from colostrum will have elevated parvoviral antibody titers. If, however, the dog has not been previously vaccinated for parvovirus, acute (now) and convalescent (10–14 days) serum antibody titers may help confirm the diagnosis. In these cases, both IgM and IgG titers should be measured.

Test code for parvovirus IgG and IgM titers is T690.