Alpha-fetoprotein: a sensitive avidine-biotin assay

A conventional enzyme-linked immunosorbent assay (ELISA) for alpha-fetoprotein was modified to incorporate the avidine-biotin complex, in order to enhance sensitivity. Five modifications of this assay were compared, of which the 2-step noncompetitive avidine-biotin assay (NABA) was found to be the most rapid and sensitive (detection limit 0.05 ng/ml). Levels of AFP in human cord serum measured by the 2-step NABA method showed good correlation (r = 0.965) with measurements by radio-immuno assay, and the assay can be performed within one hour. The simplicity and sensitivity of this assay should make it a reliable method of choice for determination of alpha-fetoprotein.