Both tests must be positive for an individual to be diagnosed with Lyme disease and fit the CDC criteria. The IgM Western blot must have 2 out of 3 bands reactive OR the IgG Western blot must have 5 out of 10 bands reactive. If the ELISA or IFA test is positive or indeterminate, it must be confirmed with the Western blot. If negative, the Western blot should not be order, according to the CDC. The two-tier diagnostic criteria requires that an ELISA screening test be performed first. The CDC recommends a two-step process when performing serological testing for Lyme disease. There are suggestions from the literature that a persistently positive IgM may reflect an ongoing infection, or a more severe disease. However, the Bb infection is unique and the IgM antibody may persist for years. The IgM would normally disappear in most infections and be replaced by the IgG class antibodies, which typically indicates the resolution of the infection. With most infections, the IgM class antibody appears first and can be used to identify an infection early on. For example, the CDC criteria does not include Bb specific antigens 31 kD and 34 kD. There are labs that report the full spectrum of bands for IgM and IgG to assist when making a diagnosis using clinical judgment. It can be difficult to interpret the results of the Western blot, since multiple “bands” need to be identified and the amount of reactivity on each determines whether or not the band will be reported. While the Western blot is more accurate than the ELISA, it has been found to not be a sensitive test. For the IgG Western blot to be positive, the CDC requires that 5 out of 10 specific Bb antigens (18, 23, 28, 30, 39, 41, 45, 58, 66, and 93 kDa) are identified. In order to have a positive IgM (immune globulin) Western blot, the CDC requires that 2 out of 3 specific Borrelia burgdorferi (Bb) antigens (23, 39 and 41 kilodalton (kDa)) are present. If enough of the antigens are present, the test is considered positive. The Western blot test identifies individual antigen patterns typically seen in Bb. The Western blot has a greater sensitivity than the ELISA. In certain cases, additional tests may be ordered, including a spinal tap or MRI. Our office typically tests for Lyme disease with both the ELISA and Western blot, and includes testing for possible co-infections. Numerous studies have found it to have a poor sensitivity rate. However, the ELISA is not an accurate screening test. If negative, the clinician may dismiss the possibility of a Lyme disease diagnosis and choose not to perform the Western blot. Typically, the ELISA test is used to initially screen for Lyme disease. The tests cannot determine if there is an active infection which could be causing the persisting symptoms, since antibodies can be produced for months or years after an infection has cleared. The ELISA and Western blot can only detect whether a person has been exposed to Bb. Both tests measure antibodies (proteins made by the immune system to fight infection) to Bb, the bacterium that causes Lyme disease. The ELISA and Western blot are the most common tests used to diagnose Lyme disease. “Effective communication and engaging your patient to elicit a complete medical history including any possible exposure to ticks is critical in making a diagnosis.” ─ Dr. Because of the varied presentations and necessity of relying on a patient’s symptoms, several tests may be helpful. That said, laboratory tests can be used to support the diagnosis. The person could have been infected with a strain of Bb that is not covered in testing. The Lyme bacteria are not always present in the blood. Antibodies to Borrelia burgdorferi (Bb) do not appear in the blood until several weeks (usually 4-6 weeks) after the tick bite. If a patient has received antibiotics in the early stage of the disease, antibody levels may be too low to be detected or nonexistent. The sensitivity of the tests varies greatly depending upon how long an individual has been infected and on the type of clinical manifestations. There can be several reasons for the inaccurate results. Yet there are numerous scientific articles documenting false negatives and low sensitivity of such tests. However, all too often, physicians will ignore clinical presentations if laboratory tests are negative. Lyme disease should be diagnosed clinically, without reliance on testing. Often the diagnosis of Lyme disease depends upon the physician’s readiness to listen.
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