A. According to many experts, there is no reliable test for Lyme disease at this time. Your doctor should base his or her diagnosis on your symptoms, medical history, and your exposure to ticks. Doctors should not rely solely on tests. There are several blood tests available, but all have limitations. The blood test typically used by most family doctors, called an ELISA (or Lyme titer) test, means nothing if it is negative, and it rarely indicates infection if it is performed too early (2 to 6 weeks after the tick bite) because your immune system has not yet made the antibodies the test is looking for.
Patients with persistent LD seldom have a positive ELISA test, possibly because they have ceased to produce the antibodies the test looks for. Many experts believe that the ELISA test is only about 30-50% accurate. While a positive ELISA test is a reasonably reliable indication of infection, a negative test is meaningless.
There are other tests that may be more accurate. The Western blot test for Lyme disease often shows infection when an ELISA test does not. Unfortunately, the U.S. Centers for Disease Control (CDC) have set arbitrary criteria for considering a Western blot test as positive for LD. These criteria were established for statistical analysis of the spread of the disease and were not intended to guide doctors in their diagnosis and treatment. The CDC surveillance criteria are very strict and miss many people with LD. Doctors who use only the CDC surveillance criteria to decide whether or not to treat leave many infected people without proper antibiotic treatment. Even if the test results are not positive by CDC standards, any positive Lyme-specific “bands” are useful indicators of infection. Another test, PCR analysis, looks for the DNA of the Lyme bacteria in blood, urine, or tissue. Multiple tests are usually required before a sample is obtained that contains the bacteria. However, in recent years PCR testing has become extremely reliable when positive. Most doctors are unaware of this test.
New tests that culture blood in a growth medium and then use PCR to detect the growing colony of Lyme bacteria show promise, as do tests that employ nanoparticles to bind to Lyme antigens.
Medical experts emphasize that LD requires a clinical diagnosis, which means that the doctor should examine the patient for typical LD signs, listen to the patient’s history and description of his or her symptoms and use this information to make a determination. Blood tests are usually done at the same time, but should not be relied upon.
According to ILADS (the International Lyme and Associated Diseases Society), if the doctor suspects LD, and sees little reason to believe the patient has some other disease, he or she should begin antibiotic treatment without delay. Of course, doctors should also perform general blood and other tests to rule out other diseases or conditions.