Clinical and Laboratory Standards Institute document M34-A—Western Blot Assay for Antibodies to Borrelia burgdorferi; Approved Guideline is intended for use as a critical tool in the diagnosis of Lyme disease for laboratorians who perform Western blot assays within clinical and reference laboratories. The document addresses the advantages and disadvantages of Western blot assays; antigen preparation; electrophoresis of antigens; transfer of antigens to the matrix; calibration of blots; quality control and proficiency testing; scoring the blot; reporting the results; and interpretation of the report. While the document specifically deals with Western blot assays for antibodies to Borrelia burgdorferi in the diagnosis of Lyme disease, the document’s generic recommendations are applicable to other situations in which Western blot assays are applied in the clinical or reference laboratory.

M34-A is intended to serve as an adjunct in the serologic diagnosis of Lyme disease. To achieve this goal, this guideline presents a comprehensive test methodology for the performance of the Western blot assay for antibodies against the organism Borrelia burgdorferi and other Borrelia spp. which have been implicated as causative agents of Lyme disease. The Western blot methods outlined within M34-A also have broad applicability over a range of other antigens and antibodies. While the interpretive guidelines contained in M34-A are specific to Borrelia species that cause disease in endemic areas in North America, it is anticipated that future expansion of these guidelines to address Borrelia species implicated as Lyme etiologic agents in other areas of the world outside of the United States will foster further global harmonization of these methods.