Some people have heard that the blood test for Lyme disease is "positive in less than 65% of cases" and believe that this applies to ALL patients and ALL stages of disease. This is not true.
The "two-tiered" blood test measures antibodies that the human body naturally makes to "fight off" infection. The blood is analyzed first with a test known as ELISA or EIA. If the result is positive or borderline, then a second test, known as a Western Blot, should be performed.
It will typically take up to several weeks after a person is infected for the test to produce a positive result. This delay is common for antibody tests. In particular, patients with a pink or reddish "bulls-eye" rash (erythema migrans) may have negative test results early in the illness. However, patients who have been ill and infected for more than a few weeks will test positive 85-100% of the time.
If you have been ill for months or years and test negative for Lyme disease using the current two-tier testing, it is unlikely that Lyme disease is the cause of your symptoms.