September 17, 2014
2 min read

Little difference in percentage of positive Lyme tests between labs

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Rates of positive Lyme disease test results were similar between a university laboratory, a commercial laboratory and two laboratories that specialize in Lyme disease testing, according to researchers from Columbia University.

“In addition to occasional differences in testing methodology, some of these laboratories provide two sets of criteria for a positive test, one based on the CDC recommendations and the other devised by the laboratory itself,” the researchers wrote in Clinical Infectious Diseases. “Some patients and clinicians believe that an [enzyme-linked immunosorbent assay] or [Western blot] obtained through a Lyme specialty laboratory may be more sensitive than comparable tests performed at a national commercial laboratory or academic center.”

The researchers obtained specimens from previous research protocols of 37 patients with Lyme disease and 40 healthy controls. The serum samples were sent for Lyme enzyme-linked immunosorbent assay (ELISA) and immunoglobulin M and IgG Western blot assays at four laboratories: one university lab, one nonspecialty commercial lab and two Lyme specialty labs (Lab A/Lab B). The two specialty labs also performed Lyme C6 peptide ELISA testing.

Among the samples from patients with Lyme disease, the labs had similar numbers of positive ELISA and IgG Western blot test results, but the number of discordant pairs between the university lab and the others ranged from eight for Lab B to 14 for Lab A. The university lab had the highest number of positive results using CDC criteria to interpret IgG Western blot: 56.8% vs. 43.2% to 48.6%. The number of discordant pairs between the university lab and the others for IgG Western blot results was similar.

When using the CDC recommended two-tiered algorithm, the university lab had a 48.6% positivity rate vs. 37.8% to 43.2% for the other labs. Compared with ELISA alone, the CDC algorithm reduced discordant pairs between the university lab and the other labs. The two specialty labs also used in-house criteria for IgG Western blots. Using these criteria, the positivity rate at Lab A dropped from 43.2% to 37.8%. At Lab B, the rate increased from 48.6% to 70.3%.

The C6 ELISA demonstrated 100% specificity at both Lab A and Lab B. Positivity was 67.6% at Lab A and 62.2% at Lab B. The IgM test performed poorly at all labs. At the university lab, there was 21.6% positivity, and positivity ranged from 2.7% to 43.2% at the other labs.

“In light of the relatively high level of discordance among laboratories, some clinicians may consider sending patient sera to a second laboratory if a case of Lyme disease is highly suspected but not confirmed by initial testing,” the researchers wrote. “However, this practice should be restricted to those laboratories demonstrated to have good specificity on these tests.”

Disclosure: The researchers report no relevant financial disclosures.