Biological variability and reference intervals for total plasma homocysteine

We determined the intra-individual biological variability of plasma homocys teine in 20 healthy subjects. The intra-individual coefficient of variation was relatively low (8.3%), indicating that a single measurement can be use d to characterize the average homocysteine concentration. A population stud y measuring plasma homocysteine and serum folate levels was conducted on se rum samples collected from 1109 randomly selected, fasting adults with a wi de age range. We determined age- and gender-specific central 0.95 intervals and found that subjects in the highest quartile of serum folate had signif icantly lower (P = 0.0001) mean plasma homocysteine concentrations than did those in the lowest quartile of folate values. An 'ideal' homocysteine ref erence range, based on targeting these subjects who are likely to be folate replete, is preferable to the population-based range using the central 0.9 5 interval.