Variables affecting apolipoprotein B measurements in 3- to 5-day-old babies: a study of 4491 neonates

To investigate the feasibility of establishing a neonatal screening program for familial type II hypercholesterolemia, we assayed apolipoprotein B (Apo B), using a radial immunodiffusion assay, in dried blood spot samples from 4491 consecutively born, 3- to 5-day-old neonates. We explored factors influencing levels at the time of sampling and factors associated with the handling of the dried blood spot samples before assay which could affect the assayed value. Assayed Apo B levels were distributed continuously and decreased with increasing delay and temperature of storage of the samples before assay. Female neonates had significantly higher mean Apo B levels than males (p less than 0.0001), with their respective means +/- SD being 0.246 +/- 0.085 g/liter (n = 2086) and 0.225 +/- 0.079 g/liter of whole blood (n = 2390). In both sexes mean Apo B levels were significantly lower in low birth weight (less than or equal to 2.5 kg) and in low gestational age (less than or equal to 36 wk) neonates. For neonates with birth weight greater than 2.5 kg and gestational age more than 36 wk, Apo B levels increased with increasing birth weight and gestational age. Sex, birth weight, and gestational age could account for 5.7% of the variability of Apo B. After adjustments for these variables, the neonate's age at sampling did not influence Apo B levels significantly. Apo B levels were not affected by different dietary regimens, whether breast-fed, formula-fed, or breast-fed with formula complement.(ABSTRACT TRUNCATED AT 250 WORDS)