There out of four commercial laboratories in the US that were sent blood samples from patients suspecting they had Lyme disease returned false-positives in up to half of all cases.
The problem was uncovered by researchers at the University of Calgary in Canada, a country that has seen an escalation of the disease in recent years.
Many Canadians who suspect they have Lyme disease-and who have similar symptoms, such as joint pain, fatigue and mental fog-are turning to the laboratories for a second opinion, especially if an initial test in Canada has failed to detect the disease.
They become "vulnerable and desperate for an answer", says Dr Dan Gregson at the university. But the American laboratories are providing a misleading diagnosis in far too many cases, which is stopping the patient receiving appropriate treatment.
Laboratories that use the standard CDC two-tier testing algorithms are most likely to return an accurate reading, he said, whereas those that employ only the Western blot method should be treated with caution.
(Source: CMAJ, August 2015; doi: 10.1503/cmaj.141413)