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Laboratory Diagnosis of Tick-Borne Infections

Part 1



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Diagnosis of Lyme Disease

Slide 25

July 2010

Currently, the CDC recommends a “2-step” approach for the serologic diagnosis of Lyme disease. In the first tier of testing, the specimen is tested by a highly sensitive screening assay, such as an EIA. If the result of the screening EIA is negative, the report should go out as Negative, and no further testing is required with the present specimen. However, in the case of short disease duration, it may be beneficial to submit a follow-up specimen in 7-14 days if clinically indicated. If, on the other hand, the result of the screening assay is positive or equivocal, the specimen should then be tested by Western blot for IgM and IgG-class antibodies.

Currently, the criteria for determining whether a Lyme Western blot is positive or negative depends on the total number of diagnostic bands determined to be present on the test strip. For instance, an IgM Lyme Western blot is positive if at least 2 of the 3 diagnostic bands are present. And for IgG, the laboratory must observe at least 5 of the 10 diagnostic bands for a positive result. Specimens meeting these criteria are reported as positive, and these results would support a clinical suspicion of Lyme disease. If these criteria are not met, the result is reported as negative and no further testing is required, except in the setting of short disease duration. If this is the case, a follow-up specimen can be tested in 1-2 weeks if clinically indicated.

I just want to emphasize one additional point regarding Lyme WB before we move on. The criteria for Lyme WB were established to guide the interpretation of serum samples, and should NOT be applied when interpreting cerebrospinal fluid serology results. To assist in the diagnosis of neuroborreliosis, we recommend that the CSF sample and a companion serum sample be submitted for Lyme antibody index testing, which is designed to assess whether intrathecal antibodies to Borrelia burgdorferi are present in CSF.  Although Lyme serology is a reliable method to assist in the diagnosis, there are several important limitations that we should discuss.

Diagnosis of Lyme Disease

 


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