Immunoglobulin M level in the diagnosis of type A hepatitis

The serum immunoglobulin M level has often but not always been found to be higher in type A than in type B hepatitis. Studies of this question, however antedated the recognition of non-A, non-B disease, and the etiologic characterization may have been mistaken in many instances. It was appropriate, therefore, to reopen the question by an investigation of 62 serologically defined cases. IgM values above 300 U/ml occurred in 28 of 33 type A episodes, three of 24 type B, and none of ten non-A, non-B cases. Although nonspecific, the IgM assay is a generally available procedure that may provide useful evidence concerning the etiologic form of acute viral hepatitis.