Improved diagnosis of neural tube defects: measurement of concanavalin A-reactive variants of AFP in amniotic fluid.

The proportion of alphafetoprotein (AFP) not reacting with Concanavalin A(Con A) was determined by crossed line affinity immunoelectrophoresis (CLAIE) in amniotic fluid obtained from 16 pregnancies with open neural tube defects and other fetal abnormalities, and 25 pregnancies with normal outcome. The percentage of Con A non-reactive AFP was significantly lower in the presence of open neural tube defects (less than 3.9%, n = 13) compared with that in normal pregnancy (range 6.4-25.2%, n = 25). In this retrospective analysis, 2 pregnancies affected by open neural tube defect escaped diagnosis on the basis of an ambiguous total AFP estimation (+2SD less than x less than +5SD) in the amniotic fluid. These observations suggest that the elimination of false diagnose based on total AFP levels may be possible, if supplementary analysis by CLAIE is performed.