Antibody to hepatitis A virus (
anti-HAV) and
IgM class antibody to HAV (
IgM anti-HAV) in sera from 73 patients with
hepatitis A and from 550 normal subjects were measured by
enzyme immunoassay (EIA) and the results were compared with those of radioimmunoassay (RIA). Since RIA has the disadvantage of requiring
radioisotopes and special equipment, the clinical applicability of EIA and possible methodological problems were evaluated. The EIA for
anti-HAV showed an excellent correlation with RIA, indicating its usefulness for the demonstration of the immune status in these subjects. Positive results of
anti-HAV were obtained in the early stage after the onset of
hepatitis A. However, pretreatment for inactivation of samples was required. False-positive reactions were found in sera to which
sodium azide was added as preservative. In the measurement of
IgM anti-HAV, a fundamental study revealed quite satisfactory results, correlation with the results of RIA was excellent. In patients with
hepatitis A, the titers reached a peak in the second to third week, followed by a gradual decline. Changes to a negative reaction were never encountered within three months. We concluded that the EIA is an useful tool in the diagnosis of
hepatitis A and can replace RIA.