Evaluation of a sensitive immunoenzymetric assay for maternal-serum alpha-fetoprotein screening. Comparison with radioimmunoassay.

An automated immunoenzymetric assay (IEMA) using monoclonal antibodies (Tandem-E, Hybritech) was evaluated for maternal serum alpha-fetoprotein (MSAFP) testing, in comparison with a classical radioimmunoassay (RIA) (Clinical Assays). The IEMA was superior in terms of sensitivity, precision, and linearity. Systematic bias between the two methods resulted in a narrower spread of clinical results, expressed as multiple-of-median, with the IEMA. Consequently, the IEMA produced fewer results that by usual criteria would be considered high (suggesting increased risk of neural tube defect) or low (suggesting increased risk of Down's syndrome). Although both methods may be comparably suitable for neural tube defect screening, the IEMA is advantageous for Down's syndrome risk assessment.