The Western immunoblot is interpreted as either positive or negative; there is no "indeterminate" with this test. IgG testing is considered positive on the Western blot if at least 5 out of 10 bands are confirmatory, while IgM requires 2 out 3 confirmatory bands.
Most patients with early disseminated or late Lyme disease have persistent antibodies for months to years.
"In no way does that correlate with the efficacy of treatment," Dr. DeBiasi stressed. "That’s a common reason people come in to the clinic. They say, ‘I want you to prove that I’m cured, and this test is negative.’ You have to explain to patients that it’s a test of antibody response, not a test for bacteria in their blood, and that just like with a vaccine, the fact that they have an antibody response is a good thing."
Many patients come in requesting the relatively new Vls C6 antibody test. It’s licensed for the diagnosis of Lyme disease, but studies indicate its sensitivity and specificity aren’t superior to the standard two-step protocol. Dr. DeBiasi reserves the Vls C6 test for travelers who may have been infected with European strains of B. burgdorferi, a situation in which it is advantageous.
She urged her colleagues not to order Lyme serologic testing for patients with fatigue, achiness, and other nonspecific symptoms in the absence of accompanying specific, objective signs of infection, such as erythema migrans or arthritis. It’s a widespread practice, but positive test results in this setting are nearly always false-positives.
Misinformation abounds regarding Lyme disease, especially on the internet. Two resources she recommends as reliable to patients are www.cdc.gov/lyme and www.idsociety.org/lyme.
Dr. DeBiasi reported having no financial conflicts.