The diagnostic significance of autoantibodies to the acetylcholine receptor.

The predictive value of the assay for antibodies to the acetylcholine receptor (anti-AChR) is dependent upon the reference range used and the question being asked by the clinician. A reference range has been established after assaying sera from 200 healthy individuals, 314 patients with diseases often considered in the differential diagnosis of myasthenia gravis (MG) or found in association with MG, and 72 patients with active adult onset MG. If the assay is to be used to screen an unselected population for MG a conservative cut off point (2 units) should be used. After establishment of a differential diagnosis more significant may be attributed to a lower result (1 unit or greater). A negative result does not exclude MG. In patients with Systemic Lupus Erythematosus. Graves' disease or thymoma anti-AChR has been demonstrated in the absence of signs of MG. Such patients may have latent or subclinical MG. Two such patients subsequently developed clinically evident MG concomitant with a rise in anti AChR titre above their particular 'biological threshold'.