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Dear Christopher Cat

We adopted a kitten from our neighbor, whose stray cat had a litter.  The veterinarian did a leukemia test, which was negative.

She said we would do Thomas’ FIV test when he was six months old, but I don’t remember why she said we couldn’t do it now.

Would you explain the tests for these two diseases?

Christopher Responds

The feline immunodeficiency virus (FIV) test detects antibodies formed to fight FIV.

The test result may be inaccurate in kittens under six months for two reasons:

Thomas could have a false positive result if his mother had FIV and he ingested antibodies through her milk.  Maternal antibodies disappear by four to six months, so if Thomas doesn’t have the virus, he will test negative after six months.

Thomas could have a false negative result if he was infected but hadn’t developed antibodies yet.  Antibodies usually form within three to four months after a bite wound from an FIV-infected cat.

Conversely, the two principal feline leukemia virus (FeLV) tests detect the FeLV virus.

Veterinarians often do an FeLV ELISA test in the office to measure virus free in the blood.  This test is more sensitive and can detect FeLV virus earlier than the FeLV IFA test which measures virus within cells, and therefore indicates persistent viral infection.

Because both FeLV tests detect the virus, not antibodies, maternal antibodies do not interfere with test results and kittens may be tested at any age.

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