Lyme disease concern: Canadians likely to get false-positives from some US labs

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Lyme disease is spreading its wings in Canada and with more and Canadians being affected, there are all the chances that few people may be looking to seek diagnosis from labs in the US.

This is according to a commentary published by experts at University of Calgary in CMAJ (Canadian Medical Association Journal).

Experts are of the opinion that Canadians who have nonspecific symptoms such as joint pain, fatigue and mental fog may assume that they may have Lyme disease and because of this assumption, they may turn to commercial US laboratories for a diagnosis. According to experts, many of these laboratories use only a single test that relies on nonevidence-based interpretation, such as the Western blot test. A positive test result that relies solely on Western blot testing is most likely a false-positive.

Recent research has found false-positive results in people without Lyme disease at 3 of 4 commercial US laboratories (ranging from 2.5% to 25%), with a rate of more than 50% of false positives at one lab.

Tests at the National Microbiology Laboratory of Canada, which uses guidelines from the US Centers for Disease Control and Prevention (CDC), are as sensitive as those used in speciality US laboratories.

“Patients with chronic subjective symptoms without a diagnosis can be vulnerable and desperate for an answer as to the cause of their illness,” writes Dr. Dan Gregson, divisions of Medical Microbiology and Infectious Diseases, departments of Pathology and Laboratory Medicine, and Medicine, University of Calgary, Calgary, Alberta, with coauthors. “Giving them a false diagnosis based on flawed testing is misleading.”

“Patients and physicians should be cautious in choosing a referral laboratory in the US when seeking ‘second opinion’ serology after receiving a negative test result in Canada,” write the authors. “Laboratories that use the standard CDC two-tier testing algorithms should be preferred over those that report results based on unproven, unvalidated, in-house criteria.”

Patients who are experiencing Lyme disease-like symptoms should receive a complete evaluation to determine the cause of their symptoms.