Lyme disease tests: CMAJ warns of false-positives from some U.S. labs
A deer tick is seen under a microscope in the entomology lab at the University of Rhode Island in South Kingstown, R.I. in March 2002. (AP Photo/Victoria Arocho)
A commentary published in the Canadian Medical Association Journal is making the case against seeking testing for Lyme disease at some U.S. commercial labs.
In the commentary, published Monday, the authors remind readers that specialty commercial labs in the U.S. do not provide a more sensitive test for Lyme disease than what's available from public health providers.
What's more, there is a high rate of false-positive test results associated with these specialty laboratories, the commentary warns.
Still some patients who receive a negative diagnosis in Canada, seek a "second opinion" with a commercial U.S. lab, the commentary says.
"Patients with chronic subjective symptoms without a diagnosis can be vulnerable and desperate for an answer as to the cause of their illness," commentary co-author Dr. Dan Gregson, from the University of Calgary, writes.
"Giving them a false diagnosis based on flawed testing is misleading."
Lyme disease is an infectious disease caused by a strain of bacteria that's typically carried by ticks.
Symptoms of Lyme disease include fatigue, fever, the development of a rash, spasms, and swollen lymph nodes. In most cases, the disease can be treated with antibiotics.
Many Canadians with non-specific symptoms such as joint pain and fatigue may turn to commercial U.S. labs because they suspect they may have Lyme disease. However, many of these labs use only a single test that relies on non-evidence based interpretation, like the Western blot, the authors say.
"A positive test result that relies solely on Western blot testing is most likely a false-positive," the commentary says.
In one recent study, cited in the commentary, false-positive results were found in three of the four specialty U.S. labs studied, with one of the labs having a false-positive rate of more than 50 per cent.
Canada's National Microbiology Laboratory uses testing guidelines from the U.S. Centers for Disease Control and Prevention, which includes two-tier testing algorithms.
"The serologic diagnosis of Lyme disease in Canada is best done using standard laboratory protocols as implemented by the National Microbiology Laboratory of Canada using criteria recommended by the Centers for Diseae Control and Prevention," the authors conclude.