Principles of heartworm testing in dogs presented for veterinary hospital employees

1. Training Module II The Heartworm Test and Heartworm Preventatives

2. Who needs a heartworm test? Wellness testing Heartworm testing in dogs over six months old is done routinely as a part of wellness testing in most parts of the U.S. In most practices, it is incorporated into the annual physical exam and/or along with routine immunizations. Sick dogs Dogs who have never had preventative or whose owners have lapsed in administering heartworm preventatives Why? It’s rare, but administering preventative to a positive dog can cause death. We had one this year—owner gave pill and his dog died in under 2 hours! Rarely, we will test cats, but it’s too complicated for this presentation.

3. Patient Selection Screening test for dogs and puppies over 6 months old Required for prescribing heartworm preventative prescriptions Recommended yearly by American Heartworm Society In our clinic, we allow dogs with a purchase history consistent with giving the pills monthly to be tested every other year. Some vets require a test yearly, and some are downright lax about testing. Coughing dogs Dogs with labored breathing Dogs with syncope (fainting) Dogs with ascites (swollen, fluid-filled abdomen) Outdoor dogs with vague clinical signs Dogs with stroke-like signs

5. Advantage Multi

6. Revolution

7. Proheart InjectionEvery six months

8. We can never truly tell if a client is faithfully giving the pill, or if their dog is actually taking the pill (as opposed to burying it in the sofa cushions or in the yard). But we do have a purchase history regarding heartworm preventatives If a client purchases the product, we assume they are administering the medication But, always ask anyway! Sometimes they will admit that they didn’t give them all Heartworm Preventative & Compliance-Is the dog actually taking the medicine?

9. What if they “missed a few months?” If the client missed one month, we tell them to give the pill and their dog needs to be retested 6-7 months after the dose was missed. We can manually insert a retest date into the Electronic Medical Record If the client missed more than a month, we require a retest before we will refill the heartworm preventative, and we also recommend retesting the patient during their next annual exam

11. Regular Patient here but buys Heartworm Rx from On-line Pharmacy?We have no record of purchase history because they buy their heartworm preventative elsewhere “Traveling vet” or mobile vets On-line Pharmacies Home-brew We require a heartworm test every 12 months. If they buy it from us, we let them go 2 years. We will not fill Rx here or approve prescriptions to outside pharmacies without a test If they are a patient of record here, we will fill Rx Inconsistent Preventative Purchase History?

12. Four types of in-house tests: Heartworm Antigen Test Direct Blood Smear Modified Knott’s Test (“Filter test”) Canine Wellness Profile on the Abaxis machine Hasn’t proven totally accurate! Recently, we ran an Abaxis heartworm test with every Canine Wellness Profile to confirm discrepancies—after 25 tests there were none Blood Tests for Canine Heartworm Infection

13. Products we prescribe/endorse here Interceptor Trifexis Advantage Multi Tri-Heart Plus

14. Heartworm Antigen Test Our mainstay heartworm test Many manufacturers We use Abaxis here Occasionally, due to a really great deal, we may have a different test kit, but most of them are similar Industry standard Tests for a protein in the blood that is associated with adult female heartworms All male infections may test negative Immature infections may test negative Most dogs do not test positive unless they have been infected for at least 5 to 6 months

15. Conducting the Test “Wet the needle” of a TB syringe with heparin before drawing blood (prevents clotting) Draw some heparin into the syringe and then shoot it all back up into the bottle

16. Open the heartworm test kit Write patient name or room number on test Add 1 drop of heparinized whole blood, serum or plasma to the test well on the left (arrow) Add 2 drops of conjugate to the test well on the left Set timer for 10 minutes Conducting the test

17. Reading the test Negative test: No Color on the left side Within 10 minutes. Only the Positive control on the right side develops color Positive Test Color develops On the left side Within 10 minutes Positive Control

18. Invalid Test/Quality Control Positive control stripe fails to develop color—means the test is invalid and must be repeated. Entire test window is opaque and bloody Blood and conjugate do not flow across the test window within 2 minutes Sometimes it helps to elevate the left side of the test by leaning it against the syringe containing the blood sample Sometimes happens if the sample clots

19. Questionable Results? Sometimes results are questionable! Very weak or almost no color development on the test stripe Clinical signs are not consistent with test results The vet thinks it’s a positive and it tests negative The vet thinks it’s a negative and it tests positive

20. What the vet may want done if results are questionable Run a direct blood smear If live microfilaria are seen, it confirms Heartworm Positive. If no microfilaria are seen, it does not confirm negative status. Further testing is needed. Do chest x-rays Send a serum sample to AViD Labs Wait and retest in 1 month

21. Direct Blood Smear Not accurate enough to be a used-alone test!!! 1 drop of heparinized whole blood on a slide Put cover slip on Tech or Vet read slide looking for living, moving microfilaria 100% accurate if microfilaria are seen If no microfilaria are seen, it still could be a positive

22. Modified Knott’s Test or Difil Test Obsolete—we no longer use this Used to concentrate microfilaria and trap them in a filter and is read by a tech under the microscope

23. Samples Sent to AViD Labs For questionable tests Is an antigen test similar to ours Run on serum Collect blood in a Vacuutainer serum separator (red top) tube Spin down the tube Transfer serum into a transfer tube Fill out AViD submission form, Call AviD for courier pickup Place sample in AViD box outside Sometimes even this is questionable!

24. The Abaxis Canine Wellness Test We have gotten some questionable results with this test Sometimes they test positive on an antigen test and negative on the Wellness rotor Sometimes they test negative on the antigen test and positive on the Wellness rotor. Recently Abaxis asked us to run one of their Antigen test kits on each patient we are doing a Canine Wellness on. We did this 25 times All of our tests agreed But we remember no test is perfect

25. Quiz The industry standard heartworm test is a. AViD Laboratories b. Direct blood smear c. Antigen test d. Modified Knott’s test We run all of the following heartworm tests except a. Modified Knott’s tests b. Abaxis Canine Wellness Profiles c. Direct blood smear d. Antigen tests

26. Quiz, continued Our heartworm antigen tests do all except a. Are semi-quantitative and tell how many heartworms the pet has b. Have built-in quality control c. Can be run on one drop of whole blood d. Take only 10 minutes Heartworm antigen tests checks for a. Heartworm microfilaria b. A protein secreted by adult female heartworms c. Heartworm ova d. Adult heartworms in the blood stream

27. Quiz, continued Minimum age for heartworm testing is 5 to 6 months One and one-half years old 3 weeks old False negative tests can occur If there is an all female worm infection If there is an all male worm infection If pet has been infected less than five to six months ago If the owner is giving heartworm preventative B & C We require a heartworm test before prescribing heartworm preventative on all dogs over 6 months old True False

28. Quiz, continued If the positive control fails to turn pink You didn’t put enough buffer. Add another drop or two Tilt the left side of the test device up by leaning it against the TB syringe you took the blood in There is something intrinsically wrong with the test kit It’s ok, sometimes they do that A Direct blood smear Is 100 % accurate all of the time Is 100% accurate if moving microfilaria are seen If no microfilaria are seen, it’s definitely negative Is so easy and cheap we should do it more

29. Quiz, continued 10. If the test results are questionable, the vet may Want you to take a chest x-ray Sent some serum out to Antech Labs Send the pet to Upstate Veterinary Specialists for a cardiac ultrasound A & B None of the above

30. Slide Presentation By Jacquelyn H. Burns, DVM Holmes Veterinary Hospital 1001 Church Street Laurens, SC 29360 (864) 984-2365 www.holmesvethospital.com Copyright © Jacquelyn H. Burns, 2011