Enzyme-linked immunosorbent assay of apolipoprotein B in blood spotted onto filter paper, suitable for neonatal screening.

This assay was developed to measure apolipoprotein (apo) B in blood samples spotted onto filter paper. The long-term aim is to detect young families with the dominantly inherited familial hypercholesterolemia, during current neonatal screening programs. The interassay CV was 5.6%, and apo B concentrations correlated closely with values measured by radial immunodiffusion. In the present assay, the primary apo B standard selected and the serum samples behaved similarly. Use of Triton X-100 in the extraction of apo B from dried blood prevented the decrease in apo B immunoreactivity that otherwise occurred during storage for 20 days at 4 degrees C. In 57 neonates two to six days postpartum, the mean (and SD) apo B concentration in whole blood was 186 (78) mg/L, and the apo A-I/apo B ratio was higher in female than in male neonates (P less than 0.001), as is also true for adults. The assay is suitable for use in screening programs for newborns, and the observations add to our understanding of lipid metabolism in neonates.