A 2-test approach for the serologic diagnosis of Lyme disease has recently been proposed. A positive or equivocal result on a first-stage test (eg, an enzyme immunoassay) is followed by a Western immunoblot test. For a sample to be considered seropositive for Lyme disease, the immunoblot result must be positive.
To assess the accuracy of IgM immunoblotting for detection of early Lyme disease and to establish interpretative criteria for a commercially available immunoblot assay.
Serum samples from 44 patients with erythema migrans were tested by an IgM immunoblot assay. All patients were culture-positive for Borrelia burgdorferi. Serum samples from 2 different control groups were also tested. Interpretative criteria were developed using receiver operating characteristic curves.
The presence of any 2 IgM bands was found to be the optimal criterion for a positive test result, and in patients with illness of less than 7 days' duration, this was significantly more sensitive than the criterion of any 2 of the 3 specific bands defined by the Centers for Disease Control and Prevention/Association of State and Territorial Public Health Laboratory Directors Lyme Disease Workgroup (P<.05). Specificity of the criterion of any 2 bands was 100% for 1 group of controls but only 96% for the more clinically relevant control group; this small difference had a large impact on the positive predictive value in populations at low risk for Lyme disease.
Using a commercially available immunoblot test kit, the presence of any 2 IgM bands is proposed as a positive result. The predictive value of a positive IgM immunoblot result, however, is poor in patients with minimal clinical evidence for Lyme disease.Arch Intern Med. 1996;156:2105-2109