Measurement of apolipoprotein B in plasma from hyperlipidemic subjects treated with cholestyramine or placebo: differential effects of storage at -70 degrees C.

Using radial immunodiffusion, we measured apolipoprotein B (apoB) concentrations in fresh plasma from 216 hyperlipidemic male subjects and in aliquots of the same plasma stored at -70 degrees C for 22 months. At the time of sampling, 112 were being treated with cholestyramine, the rest with a placebo. ApoB concentrations in the stored samples were significantly and positively correlated with apoB concentrations in the fresh samples (r = 0.84, P less than 0.001), the mean (and SD) being 1680 (320) mg/L and 1570 (320) mg/L, respectively. This 6.5% decrease in the stored samples was statistically significant (P = 0.0005), but there was no significant correlation between the decrease in apoB values in the stored samples and plasma triglyceride concentrations measured in the fresh samples. The correlation between the two apoB analyses was greater in the cholestyramine-treated group (r = 0.90) than in subjects treated with the placebo (r = 0.75).