Evaluation of amniotic fluid alpha-fetoprotein using an enzyme-linked immunosorbent assay

A simple, inexpensive enzyme-linked immunosorbent assay using commercially available supplies is described. An examination of amniotic fluid alpha-fetoprotein (AFP) values for 15 to 20 weeks' gestation is presented. The interassay coefficient of variation was 12% (N = 40) at a level of 4.75 micrograms/mL. Repeat freezing, thawing, and storage at 4C for three months had no discernible effect on measured AFP value. Data comparison with a radioimmunoassay (RIA) kit indicates similar reliability for both assays. There were no false-negative values (zero of 20). The false-positive rate for RIA was 4.4% (13 of 295) and for enzyme-linked immunosorbent assay was 5.0% (15 of 295).