Radial immunodiffusion assay of apolipoprotein B in blood dried on filter paper--a potential screening method for familial type II hypercholesterolaemia.

In the search for an effective neonatal screening programme for familial type II hypercholesterolaemia, we have developed and validated a radial immunodiffusion assay for measuring, in dried blood spots, the concentration of apolipoprotein B. The method has advantages over previously described methods, being cheaper, more robust, and suitable for partial automation. In 34 adults there was a close linear relationship between capillary and venous blood spot apolipoprotein B concentrations (r = 0.94), between capillary blood spot and serum apolipoprotein B also measured by radial immunodiffusion (r = 0.90), and between capillary blood spot apolipoprotein B and LDL cholesterol measured by ultracentrifugation (r = 0.85). Apolipoprotein B levels in serum and LDL cholesterol also correlated closely (r = 0.95, n = 40). In 30 normal 3- to 5-day old babies, heel prick blood spot apolipoprotein B levels were 280 +/- 70 mg/l (mean +/- SD) and 790 mg/l in one presumed heterozygote for familial hypercholesterolaemia. We conclude that serum apolipoprotein B measured by radial immunodiffusion accurately reflects adult LDL cholesterol levels, and that the assay, using dried blood spots on filter paper should permit both neonatal and adult screening programmes to detect familial hypercholesterolaemia.