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Canine Heartworm Testing

For dogs older than 5 ½ months
Heartworm is a parasite that is spread by mosquito bites. It can be prevented with medication. However, heartworm preventatives are not safe if used on dogs that are already infected.
If you would like Animal Control to test the dog you’re planning to adopt, tell the receptionist. The fee is $40.00.
For dogs being spayed/neutered prior to going home:
  • The heartworm test will be done at the time of surgery. If the test is positive, you will be phoned before you come to pick up the dog. If you decide NOT to take the dog after learning that the test was positive, you may get a refund OR apply the money to the adoption of another dog.
For dogs that have already been spayed/neutered and are otherwise ready to go home, you may:
  • Leave your dog at Animal Control until the test has been performed or;
  • Take your dog home and make an appointment to bring him/her back for testing in a few days. If the test is positive, Animal Control will phone you.  If you decide NOT to take the dog after learning that the test was positive, you may return the dog and get a refund OR apply the money to the adoption of another dog.
If you decide to keep a dog that tested positive for heartworm, you should consult with your private veterinarian about the disease and how it may affect your particular dog. You, not Anne Arundel County Animal Control, are responsible for the cost of caring for your pet.
Test Results
The following are possible interpretations of positive and negative test results. You should consult with your private veterinarian for specific advice concerning your pet.
Heartworm Negative
A negative result almost always means that your dog does not have an active infection with adult heartworms at this time. It is probably safe for your private veterinarian to start your dog on preventative medication. Heartworm is spread by bites from infected mosquitoes and, because of the time lapse between being bitten by an infected mosquito an the appearance of enough heartworm proteins in your dog’s blood to make the test register positive, there is a small possibility of a false negative test result. Consult your private veterinarian regarding the appropriate preventative medication for your dog and the interpretation of the test results.
Heartworm Positive
This means that your dog probably has adult heartworms in his/her blood today. 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. Heartworm is a serious, even life threatening disease, but it can be treated. If it is caught before your dog’s heart and lungs are damaged by the parasite, most dogs do extremely well. The cost of treatment varies greatly depending upon the amount of diagnostic work needed and the damage the parasite has caused before being detected. Consult your private veterinarian.
What is a false negative test?
This happens when your dog is infected with adult heartworms and the test fails to detect their presence. Early infestations, very low numbers of parasites, and infestation with mostly male worms are the most common causes of false negatives. False negative heartworm tests are rare.
What is a false positive test?
A false positive test result occurs when the test comes out positive, but your dog does not have adult heartworms in his/her body at this time. It is impossible to tell the difference between a false positive and a true positive result with a single test, so your veterinarian will probably retest the dog or do a different test. False positives are unusual.

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Anne Arundel County, Maryland. 44 Calvert Street, Annapolis, Maryland 21401 | Tele: (410) 222-7000