Lyme Disease testing algorithm/CDC
Positive WB for Lyme disease/CDC
Diagnosis can be made from a characteristic clinical picture, but not all patients present with a classic erythema migrans lesion.
Atypical lesions: CDC
A serological testing approach is used to obtain laboratory diagnosis. A two-step testing procedure is recommended by the CDC, as outlined in the top image on the right. 60 to 70% of enzyme immunoassay (EIA), enzyme-linked immunosorbent assay (ELISA), or immunofluorescence assay (IFA) tests are positive by week four. For this reason, an EIA (rarely IFA) is performed as the first step. If the EIA/IFA is positive or equivocal (indeterminate), the CDC recommends that an immunoblot (commonly a Western blot) test is performed as the second step.
If the patient has had symptoms ≤ 30 days, perform both the IgM and IgG Western blots (WB). If the patient has had symptoms ≥ 30 days, just perform the IgG WB. When interpreting the IgG WB, it is required that at least five IgG bands are detectable, as shown in the lower image on the right.
False-positive EIA/ELISA tests may be caused by numerous infections and conditions; thus, the need for a confirmatory WB. Some of the more common false-positive results are seen in:
- Tick-borne relapsing fever
- Some autoimmune disorders (eg, 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)
The ELISA test is very sensitive, so if it is negative, go no further unless symptoms persist. Then, repeat the ELISA or IFA at a later time. Cultures can be performed, but the yield is low (only about 27% in one study). Polymerase chain reaction (PCR) is also not very sensitive (positive about 50% of the time). This is primarily because it is difficult to choose the specimen most likely to yield a positive test.
There are limitations to testing. For one thing, there is not a Food and Drug Administration (FDA) approved rapid test, nor is there an antigen test available. Decay of antibodies is unpredictable; therefore, you cannot determine if a positive test result is a new infection or a previous one. Furthermore, there is no test to determine if the patient is cured.
Several laboratory-developed tests have come under scrutiny. The CDC has issued warnings against many of these because they can be inaccurate.