Recent studies have documented that antigen tests may not test positive in up to 7% of dogs due to the occurrence of “antigen-antibody complexes” that are formed in the dog's blood. These complexes bind the circulating antigen so that it is “unavailable” to react on the antigen tests.
Is it possible to have a false positive heartworm test?
Heartworm Positive Do not give your dog any heartworm preventive medication if today's test was positive. False positive tests occasionally occur, so it is important that you consult your veterinarian for follow-up advice. A second test will probably be done.
How accurate is heartworm antigen test?
Depending on prevalence, the positive predictive value of the heartworm antigen test ranged from 15 to 54% and negative predictive value from 99 to 99.9%. For a hospital testing 1,000 dogs per year, false-positive test results may vary from 24 to 27 dogs.
What could cause a false positive heartworm test?
Known causes of false positive heartworm antigen tests include infection with Spirocerca lupi, Angiostrongylus vasorum and A. odendhali, while related nematodes, such as other Dirofilaria spp., Dracunculus insignis and Onchocerca spp., are also thought to induce false positive results [49,50,51,52,53].
What does a positive heartworm antigen test mean?
They are the fastest and most convenient way to test for heartworms, but no test is perfect. False positives and false negatives are possible. That is why positive tests are always confirmed with another method of testing. Usually, a positive antigen test is confirmed with presence of microfilaria in the blood.
Which would be detected by the typical antigen heartworm test in dogs?
There are two main tests for detecting heartworm infection; one test detects adult worms and the other detects microfilaria. Testing for Adult Worms: The American Heartworm Society recommends that a Heartworm Antigen Test should be the primary method of testing for adult heartworm infection.
What is a weak positive heartworm test?
A weakly positive in-clinic test result is likely positive, but the result can be confirmed by repeating the test or ordering a reference lab test. If results are discordant between in-clinic and laboratory tests, Dr. Herrin advises trusting the reference lab result.
Can a dog get a false negative heartworm test?
False-negative antigen tests occur most often in heartworm-infected animals when the host immune response traps circulating D immitis antigen in antigen—antibody complexes, preventing it from reacting with commercial assays.
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