Understanding the EIA Test
Several types of EIA tests exist. Validated and FDA-approved EIAs include “ELISA” (enzyme-linked immunosorbent assay and “ELFA” (enzyme-linked fluorescent immunoassay). Lyme disease testing measures a person's antibody (or immune response) to the bacteria that cause Lyme disease. EIA tests are designed to be very "sensitive”, meaning that when they are used properly, almost everyone with Lyme disease will test positive. It is also possible, however, to test positive with an EIA test even when you do not have Lyme disease. This can occur because of other medical conditions, including:
- Tick-borne relapsing fever
- Anaplasmosis (formerly known as granulocytic ehrlichiosis)
- Some autoimmune disorders (e.g., lupus)
- Bacterial endocarditis
- Infection with Helicobacter pylori, Epstein Barr virus, or Treponema denticola (bacteria found in the mouth that can cause gum disease and/or infection after dental procedures)
For this reason, doctors want to verify any "positive" or “equivocal” (indeterminate) EIA results by performing an immunoblot test such as a Western blot. The Western blot or other FDA-approved type of immunoblot can help distinguish patients who have Lyme disease from those with other conditions.
Additional information on the EIA/ELISA test is available.
New tests may be developed as alternatives to one or both steps of the two-step process. Before CDC will recommend new tests, their performance must be demonstrated to be equal to or better than the results of the two-test procedure. For more details, see Recommendations for Test Performance and Interpretation from the Second National Conference on Serologic Diagnosis of Lyme Disease.