According to many experts, there is no reliable test for Lyme disease and many other tick-borne diseases at this time. Your doctor should make a clinical diagnosis based on your symptoms, medical history, and exposure to ticks. Doctors should not rely solely on tests. There are several blood tests available, but none are completely reliable. The blood test most typically used is called an ELISA (or Lyme titer) test. The test results may mean nothing if it is negative, and it rarely indicates infection if it is performed too early (2 to 6 weeks after the tick bite).
Patients with persistent Lyme Disease and other TBDs seldom have a positive ELISA test, possibly because they have ceased to produce the antibodies detectable by the test. Many experts believe that the ELISA test is only about 30-60% accurate. The ELISA test is not based on the specific Lyme bacteria strain that is most useful for accurate diagnosis. While a positive ELISA test is a reasonably reliable indication of infection, a negative test is useless.
The Western blot test for Lyme Disease (LD) often shows infection when an ELISA test does not. Unfortunately, the U.S. Centers for Disease Control (CDC) have set strict 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 miss many people with LD. Doctors who use only the CDC guidelines to decide whether or not to treat leave many infected people without 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.