What Is a Light Positive Lyme Test in Canines?

Lyme disease is a bacterial infection typically passed to dogs after a bite from a deer tick. While the disease is curable, treatment can be expensive and painful for the dog. Most dogs with Lyme disease don't immediately show symptoms, but if your dog is lethargic, has localized skin swelling and redness, or has recently been bitten by a tick, you should consult your vet. There are several tests available for Lyme disease, and a light positive test generally indicates a low level infection or an error in testing procedure.

  1. Lyme Disease Test

    • The most commonly used Lyme disease test is a simple blood draw called the 3Dx test that tests for a number of parasites. Some veterinarians use a blood test called the 4Dx test that tests for anaplasmosis, another tick-borne disease. Referring to these tests as Lyme disease tests, however, can be a bit misleading. Blood tests can't actually test for Lyme disease. Instead, they test for heightened levels of bacterial pathogens associated with Lyme disease in the blood. The presence of pathogens can indicate either exposure or infection, and a "light positive" Lyme disease test typically requires a follow up.

    Lyme Disease Vaccination

    • Although it is not part of the group of vaccinations most commonly administered to dogs, a Lyme disease vaccine is available. This immunization produces immunity to the disease by exposing your dog to a low-level, non-threatening number of Lyme disease pathogens. If your dog was recently vaccinated against the disease, a light positive result on a test is most likely due to the immunization, so make sure your vet has your dog's complete immunization records.

    False Positive Results

    • Lyme disease test results that are only faintly positive are almost always repeated because of the potential for a false positive. If the test only shows a small number of pathogens, it may be that the blood sample was contaminated or the test was read incorrectly, so ask your veterinarian about repeating the test again in a few days.

    Infection and Treatment

    • For most dogs, a light positive test occurs in the early stages of the disease, before symptoms have become apparent. Ask your vet about beginning immediate treatment for the illness. The good news is that the earlier the disease is caught, the less difficult treatment is likely to be because your dog is not already fighting off a heavy bacterial load.