The 4dx Test Demystified

posted: by: Margaret Eastman, DVM Tags: "Clinic Specials" "News" 

It used to be a right of spring, like putting away the snow blower. Now that the pharmacology of heartworm preventatives have changed and we generally give preventatives year round, the annual “heartworm test” can be performed with your dog’s annual exam and vaccination. For years, the blood test for heartworm was quite reliable. More recently, the folks at Idexx have added additional tests so this annual event yields yet more information on your pet’s exposure to tick-borne disease.

When we give you the results for your dog’s heartworm test, the report looks like this:

AP_spp             Negative

EC-EE              Negative

HW                  Negative

Lyme               Negative

All those negatives are great, but a positive isn’t the end of the world. Here’s the legend for your results:

AP_spp:  Anaplasmosis

Anaplasmosis is a tick-borne rickettsial bacteria that is commonly found in the Midwest.  Dogs who are sick from Anaplasma may experience fever, lethargy and a decreased appetite. Most dogs who are affected show no obvious symptoms. If one of our healthy patients comes up positive for Anaplasma (and they often do), we check a complete blood count to make sure the platelet count is normal.


EC-EE: Ehrlichia

Ehrlichia, also a tick-borne rickettsial bacteria can cause similar symptoms to Anaplasmosis. However some of these patients can become quite ill over time. They can develop limb swelling, bleeding disorders, and enlarged internal organs as well as lymph nodes. And some never show any symptoms at all. As with Anaplasma, dogs who give us a positive EC-EE result and feel fine get a CBC checked to make sure their platelets and red cells are normal.



We’ve all heard of lyme disease, and in some parts of the country it’s more likely your dog will test positive than it won’t if it spends any time in the woods. If we get a positive lyme result in a dog who feels fine, we check a urine sample for the presence of protein. Dogs who develop symptoms due to their lyme disease may experience fever, enlarged lymph nodes, shifting lameness, and joint swelling. They may also develop kidney disease – thus the protein in the urine.


HW: Heartworm

This result is pretty straightforward. It can take at least six months for a heartworm infection to develop to the stage where it can be detected with this very sensitive test. For this reason we often hold off on testing puppies and adults new to our area until there’s a window of exposure that could yield a positive result. For more information on heartworm disease, you can refer to my previous post.


So what does a positive on a tick-borne disease mean?  On this test, it means your dog was exposed. If the CBC or urinalysis is normal, we make a note and it goes no farther than that. If we find an abnormal result from our lab work, we may put your dog on the appropriate antibiotic, then recheck the lab work to see if the abnormalities resolve.

Probably the most valuable aspect of this test relates to you, the human side of the equation. If your dog is being exposed to tick-borne disease, you probably are as well. It’s important to take measures to minimize tick attachment for both you and your dog. Products like Frontline and NexGard play an important role in tick control, but don’t forget to dress appropriately and check yourself for ticks when you and your dog have been enjoying the wonders of nature together.

I hope this helps demystify the results of your dog’s 4Dx test. We live in a beautiful part of the country, and ticks are definitely the trade off. Hopefully having this additional information with your dog’s heartworm status will add to your peace of mind when enjoying the great outdoors.