- What laboratory techniques are used to carry out the assay?
- What exactly is being measured?
- What is a "band"?
- How are the results interpreted?
- What are the CDC criteria for a "positive" test?
Although some of the medical jargon associated with immunology can be a little overwhelming, the scientific principles behind these tests are not difficult to grasp. The following article is offered as a primer in the techniques and interpretation of Western blotting, and should help most patients navigate their way through some of the medical and scientific terminology associated with the assay.
First of all, it should be noted that the Western blot is usually performed as a follow-up to an ELISA test, which is the most commonly employed initial test for Lyme disease. "ELISA" is an acronym for "enzyme-linked immunosorbent assay." There are ELISA tests and Western blots for many infectious agents; for example, the usual testing regime for HIV is also an initial ELISA followed by a confirmatory Western blot.
Both the ELISA and the Western blot are "indirect" tests -- that is, they measure the immune system's response to an infectious agent rather than looking for components of the agent itself.
In a Lyme disease ELISA:
- Antigens (proteins that evoke an immune response in humans) from Borrelia burgdorferi (Bb) are fixed to a solid-phase medium and
- Incubated with diluted preparations of the patient's serum. If antibodies to the organism are present in the patient's blood, they will bind to the antigen.
- These bound antibodies can then be detected when a second solution, which contains antibodies to human antibodies, is added to the preparation. Linked to these second antibodies is an enzyme which changes color when a certain chemical is added to the mix.
- Although the methodology is somewhat complicated, the basic principle is simple: the test looks for antibodies in the patient's serum that react to the antigens present in Borrelia burgdorferi. If such antibodies exist in the patient's blood, that is an indication that the patient has been previously exposed to B. burgdorferi.