Heartworm Antigen Test

A variety of commercial test kits are available for the serological diagnosis of Dirofilaria immitis.


Purpose

A variety of commercial test kits are available for the serological diagnosis of Dirofilaria immitis. These tests are used to detect antigen from adult female worms in canine whole blood, serum or plasma.

Principle

A heartworm antigen serology test is an enzyme-linked immunosorbent assays (ELISA) that uses antigen specific antibodies to detect D. immitis antigen from adult female parasites in blood, serum or plasma. The sample and conjugate are combined and added to the test’s sample well. If the sample contains D. immitis antigen then the sample will bind with the antigen specific antibodies in the test well and will return a positive result.

Variations

There are a number of different commercial heartworm antigen test kits available for dogs, all of which are based on ELISA technology and on serological detection of D. immitis antigen. The antigen tests are not as effective in diagnosing heartworm in cats since these hosts more often have all male or immature female parasites in which antigen cannot be detected. In cats serological tests are based on detecting antibody to D. immitis. These do not indicate a current infection, however, simply exposure that had occurred previously.

Benefits

Heartworm antigen tests are very convenient for in-clinic use since they are easy to use, quick, cost effective, accurate and don’t require any skill in parasite identification.

Problems

If the dog is infected with only male worms and/or immature female worms, neither of which produce antigen, the heartworm antigen test will return a negative test result despite infection. Antigen is not detectable until about 5 months post-infection so the test will give a false negative result in infected dogs if done prior that time.

In areas where heartworm is not endemic the likelihood of getting a false positive result from a serological heartworm test is much higher than in an area where it is endemic. The lower prevalence of the infection results in a lower positive predictive value and thus a lower specificity and higher likelihood of getting a false positive test result.

 

References

American Heartworm Society Website:  http://www.heartwormsociety.org/
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