In North America, Lyme disease (LD) is caused predominantly by the spirochete Borrelia burgdorferisensu stricto, and is transmitted by blacklegged ticks. Long Island, New York, is highly endemic for the disease. The C6 peptide (C6P) is currently used as a screening test for LD in our institution. Our objective was to examine how screening with C6P concorded with diagnosis of LD at the Veterans Affairs Medical Center, Northport, Long Island. A retrospective chart-review of 2558 C6P tests was performed during the period of 1/1/2010 to 12/31/2016. Patients were categorized by Lyme Disease (LD) or no LD groups. LD group was defined as having an erythema migrans (EM) rash, or ≥ 2 IgM bands or ≥ 5 IgG bands on immunoblot. Out of the 409 patients with positive or equivocal C6P, 181 patients with LD were based on presence of EM, or Western blot IgM and IgG test results; 228 did not have LD. The positive predictive value of C6P was 44.5%. EM was the most common presentation. In the LD group, history of tick bite (P: 0.0001), headache (P: 0.0036), joint swelling (P: 0.0086) and myalgias (P: 0.0005) were more likely to be present. Zip code mapping of our cases mirrored those previously reported in the Suffolk County Department of Health. In our review we encountered a significant number of false positive C6 assays. False positive C6P tests were ordered by primary care physicians (PCP) (37%) followed by neurologists (33%). A history of tick exposure and clinical findings of early Lyme disease such as headaches or joint aches were more likely to denote a true positive C6 peptide test. Rigorous education of physicians about Lyme disease and pitfalls of our available diagnostic tests are needed for their proper utilization.
Keywords: Borrelia burgdorferisensu stricto; C6 peptide; Lyme disease; Western blot.
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