Maternal alphafetoprotein screening by the polypropylene tube immunoradiometric assay on dried blood.

The polypropylene tube immunoradiometric assay for alphafetoprotein (AFP) determination was applied to maternal serum along with a radioimmunoassay technique during the second trimester of pregnancy. Blood from pregnant women was collected by finger prick on strips of chromatography paper (Schleicher and Schuell No. 903C) and air dried. A 4.75 mm disc spot was eluted in anti-AFP coated tubes containing 1.0 ml of assay medium. After one hour the medium was vortexed and the tubes washed and counted on a Concept 4tm (Micromedic Systems, Horsham, PA. 19044). The sensitivity of the technique is about 9 micrograms/l (35 ng/l in the assay) by the Rodbard formula. The concordance between the dried blood and the serum RIA tests in normal pregnancies was over 90 per cent at the 95th and 97th percentiles. This assay on dried blood spotted on chromatography paper was tested on 1003 patients and proved to be an ideal alternative to whole serum screening techniques: it minimizes sample manipulations and can easily be integrated into an existing newborn screening programme.