Heartworm testing

[Ayemee]

Hello guys,

I work as a vet assistant and I’m a little confused about the protocol to heartworm testing. I don’t work until Saturday and it’s driving me nuts haha.

1. A dog can be on HW prevention until 7 mos, but once 7 mos, they should be tested for heartworms to be able to continue HW prevention.

- My Q: what if they haven’t been regular with the HW prevention? Should you still test? To me, i don’t think it’d matter since either way, it’s been long enough for the heartworms to show up positive on the test.

2. A dog comes in and is at least 7 months and has never been on HW prevention, we should go ahead and test for heartworms.

3. A dog that is 3 yrs old comes in, and has been irregular on HW prevention. We can still test, correct?


My big Q is why can’t we test a dog for heartworms thats at least 7 mos old if the owner has not kept the dog on heartworm prevention each month? Either way...it shouldn’t affect the test, I don’t think?

I had a dog come in yesterday at work who was 8 mos and I was going to do a 4DX test but the doctor said since the patient hasn’t received HW prevention for 2-3 months, we can’t do the test.

Confused

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[pinkpuppy9]

Hello guys,

I work as a vet assistant and I’m a little confused about the protocol to heartworm testing. I don’t work until Saturday and it’s driving me nuts haha.

1. A dog can be on HW prevention until 7 mos, but once 7 mos, they should be tested for heartworms to be able to continue HW prevention.

- My Q: what if they haven’t been regular with the HW prevention? Should you still test? To me, i don’t think it’d matter since either way, it’s been long enough for the heartworms to show up positive on the test.

2. A dog comes in and is at least 7 months and has never been on HW prevention, we should go ahead and test for heartworms.

3. A dog that is 3 yrs old comes in, and has been irregular on HW prevention. We can still test, correct?


My big Q is why can’t we test a dog for heartworms thats at least 7 mos old if the owner has not kept the dog on heartworm prevention each month? Either way...it shouldn’t affect the test, I don’t think?

I had a dog come in yesterday at work who was 8 mos and I was going to do a 4DX test but the doctor said since the patient hasn’t received HW prevention for 2-3 months, we can’t do the test.

Confused

I'm thinking your doctor may be considering the life cycle and wanting to test the dog in 3 more months (since the dog has been off prevention for 3 months) but I could be wrong about his/her intentions. Being on/off heartworm prevention does not impact test results other than the test hopefully being negative because the dog is heartworm free You can test any dog at any time regardless of preventative status. It's not necessarily 'wrong' to test now, but a skipped month(s) = window for heartworm infection and negative now does not mean negative in 6 months or a year. I've seen newly adopted dogs test negative at adoption, only to be positive at their next yearly snap after being on 12 months of prevention. It happens, it takes a lot of explaining to clients.

Maybe someone else has more insight, I can only think of the 6-month infection maturity rule as a possible explanation here.

 

[Ayemee]

I'm thinking your doctor may be considering the life cycle and wanting to test the dog in 3 more months (since the dog has been off prevention for 3 months) but I could be wrong about his/her intentions. Being on/off heartworm prevention does not impact test results other than the test hopefully being negative because the dog is heartworm free You can test any dog at any time regardless of preventative status. It's not necessarily 'wrong' to test now, but a skipped month(s) = window for heartworm infection and negative now does not mean negative in 6 months or a year. I've seen newly adopted dogs test negative at adoption, only to be positive at their next yearly snap after being on 12 months of prevention. It happens, it takes a lot of explaining to clients.

Maybe someone else has more insight, I can only think of the 6-month infection maturity rule as a possible explanation here.

But even if the dog was off of the HW prevention for 3 months and is 8 months old, how would it change things by waiting another 3 months? The heartworms are already at the point where they can be diagnosed from a test

 

[Lupin21]

But even if the dog was off of the HW prevention for 3 months and is 8 months old, how would it change things by waiting another 3 months? The heartworms are already at the point where they can be diagnosed from a test

Each test is expensive. Knowing it has only had 3 months of lapse means the client's money is best spent from that window on rather than having to retest again.

 

[Ayemee]

Each test is expensive. Knowing it has only had 3 months of lapse means the client's money is best spent from that window on rather than having to retest again.

But why would you have to re-test? If the dog had heartworms, it would show up positive one way or the other.

 

[Lupin21]

But why would you have to re-test? If the dog had heartworms, it would show up positive one way or the other.

Yes, but if it was infected in that three month window, it would be negative, and you would have to retest anyway in three months again to confirm a negative. Two tests. Expensive.

 

[Ayemee]

Yes, but if it was infected in that three month window, it would be negative, and you would have to retest anyway in three months again to confirm a negative. Two tests. Expensive.

I get what you’re saying but why when a dog comes in over a year old and hasn’t been on heartworm prevention for 6 mos, we go ahead and test. Then test annually there on regardless if they haven’t been regular with the hw prevention? Unless they come in and say their dog hasn’t been on hw prevention for at least 6 months, then yes, we go ahead and retest.

Does that make sense where my confusion arises?

 

[Lupin21]

I get what you’re saying but why when a dog comes in over a year old and hasn’t been on heartworm prevention for 6 mos, we go ahead and test. Then test annually there on regardless if they haven’t been regular with the hw prevention? Unless they come in and say their dog hasn’t been on hw prevention for at least 6 months, then yes, we go ahead and retest.

Does that make sense where my confusion arises?

You need to understand that the test detects adult female worm reproductive antigen. It takes six months from infection to adulthood for the worms. Therefore, any lapse in prevention, you have to count from that point on to when you see the animal for determining the best time for testing for which the infection date on has been six months.

Another point is that people sometimes skip a month without knowing it or even if they are giving the product, there may be a lapse somewhere else, so yearly testing makes sure the dog is indeed still negative. This also allows for a record in case the dog comes down positive so the company can pay for treatment and record the evidence for signs of resistance.

 

[Ayemee]

You need to understand that the test detects adult female worm reproductive antigen. It takes six months from infection to adulthood for the worms. Therefore, any lapse in prevention, you have to count from that point on to when you see the animal for determining the best time for testing for which the infection date on has been six months.

Another point is that people sometimes skip a month without knowing it or even if they are giving the product, there may be a lapse somewhere else, so yearly testing makes sure the dog is indeed still negative. This also allows for a record in case the dog comes down positive so the company can pay for treatment and record the evidence for signs of resistance.

That makes sense - so if a two year old dog comes in but has only been on prevention for two months, would we wait until the full 6 month period to test? Basically, is that the rule for no matter what age?

What would you do if a owner came in and said he wanted to update his 4DX but knows he missed a few months throughout the year. It’s still okay to test?

 

[Lupin21]

That makes sense - so if a two year old dog comes in but has only been on prevention for two months, would we wait until the full 6 month period to test? Basically, is that the rule for no matter what age?

Unless of course you want to know right there and there, and don’t mind retesting.

correct. The animals age has nothing to do with it, other than it is pointless to test an animal less than six months of age. That is again, due to the worm's cycle, not the age of the dog.

 

[Ayemee]

correct. The animals age has nothing to do with it, other than it is pointless to test an animal less than six months of age. That is again, due to the worm's cycle, not the age of the dog.

Okay! Makes sense!

Thanks a lot for your help, I was really racking my brain over this.

 

[Cephal0pod]

Here are a couple of handy resources if you would like to learn more. The CAPC (Companion Animal Parasite Council) website linked below is also great for most other parasites you will deal with/talk with clients about in a small animal general practice setting.

Home

Founded During The Heartworm Symposium Of 1974, The American Heartworm Society Aims to further scientific progress in the study of heartworm disease inform the membership of new developments, encourage and help promote effective procedures for the diagnosis, treatment and prevention of heartworm...

www.heartwormsociety.org

Heartworm

capcvet.org