A heartworm test is a blood test designed to check for evidence of the roundworm parasite, Dirofilaria immitis, more commonly known as heartworm. The test should be performed on any cat in which heartworm is suspected. Typically, these are cats showing signs of coughing, dyspnea, vomiting, lethargy, anorexia, and weight loss.

There is no contraindication to performing this test. Normal cats test negative for heartworm. Negative results help rule out the existence of heartworm disease.

What Does a Heartworm Test Reveal?

There are two different tests used to check for heartworms in dogs, but only one of these has been found effective in cats.

Microfilaria test: Microfilaria are "heartworm babies." Screening for them is rarely done in cats because it is often negative even when heartworms are present. The reasons for microfilaria being absent from the bloodstream when adult worms are present include:

Only a single heartworm being present (thus no mating of worms is possible).

The infection is with either all male or all female worms.

The cat's immune system is actively destroying the microfilaria as they are being produced.

Antigen Testing: Heartworm antigen tests detect antigen derived primarily from mature female worms. Immature infections, low worm burden, male only infection, or sexually immature worms may not produce enough antigen for detection. Also, cats may take a while after infection to develop positive antigens.

How Is a Heartworm Test Done?

Heartworm testing involves drawing a blood sample. The blood is placed immediately in a glass container with a substance that prevents clotting of the sample. The sample is then submitted to a laboratory. The canine heartworm test cannot be used to detect feline heartworm disease. It takes 1 to 2 days to obtain the results of the test.

Is a Heartworm Test Painful?

In order to obtain a blood sample, a needle must be passed through the skin and into a blood vessel. As with humans, the pain associated with venipuncture will vary from individual to individual, but is no more painful than any other injection.

Is Sedation or Anesthesia Needed for a Heartworm Test?

Sedation or anesthesia is not needed for a heartworm test.