Training Module IIThe Heartworm Test and

Heartworm Preventatives

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 dogsDogs 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.

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

Heartworm PREVENTATIVES

Oral monthly◦Ivermectin-based

Heartgard Plus Iverheart Plus Tri-Heart Plus Iverheart Max

◦Milbemycin-based Interceptor Sentinel Trifexis

• Topical Monthly• Advantage Multi• Revolution

• Proheart Injection

Every six months

Heartworm Preventative & Compliance-Is the dog actually taking the medicine?

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

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 RecordIf 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

Inconsistent Preventative Purchase History?

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 will not fill Rx here or approve prescriptions to

outside pharmacies without a test

• Transferred records here from another vet with record of negative test within the last 12 months and record of consistent purchase history

If they are a patient of record here, we will fill

Rx

• Regular Patient here but buys Heartworm Rx from On-line Pharmacy?

We require a heartworm test every 12 months. If they buy it from us, we let them go 2 years.

Blood Tests for Canine Heartworm Infection

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

Products we prescribe/endorse here

InterceptorTrifexisAdvantage MultiTri-Heart Plus

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 heartwormsAll male infections may test negativeImmature infections may test negative

◦Most dogs do not test positive unless they have been infected for at least 5 to 6 months

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

Conducting the test

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

Reading the test

Positive TestColor develops On the left side Within 10 minutes

Negative test: No Color on the left sideWithin 10 minutes. Only the Positive control on the right sidedevelops color

Positive Control

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 bloodyBlood 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

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

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-raysSend a serum sample to AViD LabsWait and retest in 1 month

Direct Blood Smear

Not accurate enough to be a used-alone test!!!

1 drop of heparinized whole blood on a slide

Put cover slip onTech 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

Modified Knott’s Test or Difil Test

Obsolete—we no longer use thisUsed to concentrate microfilaria and trap

them in a filter and is read by a tech under the microscope

Samples Sent to AViD Labs

For questionable testsIs an antigen test similar to oursRun 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!

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

Quiz

1. The industry standard heartworm test isa. AViD Laboratoriesb. Direct blood smearc. Antigen testd. Modified Knott’s test

2. We run all of the following heartworm tests excepta. Modified Knott’s testsb. Abaxis Canine Wellness Profilesc. Direct blood smeard. Antigen tests

Quiz, continued

3. 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

4. Heartworm antigen tests checks fora. Heartworm microfilaria

b. A protein secreted by adult female heartworms c. Heartworm ova d. Adult heartworms in the blood stream

Quiz, continued

5. Minimum age for heartworm testing isa. 5 to 6 monthsb. One and one-half years oldc. 3 weeks old 6. False negative tests can occur

a. If there is an all female worm infectionb. If there is an all male worm infectionc. If pet has been infected less than five to six months agod. If the owner is giving heartworm preventativee. B & C

7. We require a heartworm test before prescribing heartworm preventative on all dogs over 6 months old

a.Trueb.False

Quiz, continued

8. If the positive control fails to turn pinka. You didn’t put enough buffer. Add another drop or twob. Tilt the left side of the test device up by leaning it against the

TB syringe you took the blood inc. There is something intrinsically wrong with the test kitd. It’s ok, sometimes they do that

9. A Direct blood smeara. Is 100 % accurate all of the timeb. Is 100% accurate if moving microfilaria are seenc. If no microfilaria are seen, it’s definitely negatived. Is so easy and cheap we should do it more

Quiz, continued

10. If the test results are questionable, the vet mayA. Want you to take a chest x-rayB. Sent some serum out to Antech LabsC. Send the pet to Upstate Veterinary Specialists for a cardiac

ultrasoundD. A & BE. None of the above

Slide Presentation By

Jacquelyn H. Burns, DVMHolmes Veterinary Hospital 1001 Church Street Laurens, SC 29360 (864) 984-2365 www.holmesvethospital.com

Copyright © Jacquelyn H. Burns, 2011