Reference distributions for apolipoproteins AI and B and the apolipoprotein B/AI ratios: a practical and clinically relevant approach in a large cohort.
The two serum apolipoproteins in the highest concentrations, apolipoprotein (apo) AI and apolipoprotein B, and the apolipoprotein B/AI ratio are measured to assess clinical risk for atherosclerotic heart and peripheral vascular diseases. The study is based on a cohort of over 37,000 Caucasian individuals from northern New England measured in one laboratory by immunonephelometry using standardized reference materials. All samples received for protein analyses were accepted provided adequate identifying information was available. Laboratory and demographic information was entered into a single database for subsequent study. Our results show that for males without evidence of inflammation, values of apo AI change little through life. For females, however, values gradually increase until about 60 years of age then fall somewhat thereafter. Among adults, females have higher apo AI values on average, than males. Apo B values change significantly through life, increasing after the end of the second decade to a peak during the sixth decade, then falling thereafter. In the past, concern has been expressed that apo AI is an acute phase reactant (APR), thus complicating cardiovascular risk assessment. The effects of an APR (C-reactive protein >or=10 mg/L) on apo AI, but not on apo B, are measurable for both sexes, most noticeably beyond the age of 60 years in males and females. When values were expressed as age- and gender-specific multiples of the median (MoMs), the resulting distributions fit a log-Gaussian distribution well over a broad range. The size of the relatively homogenous cohort, by a standardized approach, provides a firm basis for comparison to preexisting reference intervals and for establishing a clinically useful and current reference interval for the three main apolipoprotein values.