Results of B-vitamin supplementation study used in a prediction model to define a reference range for plasma homocysteine.

Because high plasma concentrations of homocysteine constitute an enhanced risk for premature coronary heart disease, it is necessary to establish a reference range for normal concentrations of plasma homocysteine. The frequency distribution of plasma homocysteine concentrations tails to the right, and the nonparametric approach is unsatisfactory for defining a normal plasma homocysteine reference range. By using subjects' responses to appropriate vitamin supplementation, we developed a mathematical prediction model to calculate the plasma homocysteine concentration that could be expected for each individual treated with a vitamin supplement. With this model, we can predict that plasma homocysteine concentrations will approach a normal frequency distribution with a 95% reference range (mean +/- 2 SD) of 4.9-11.7 mumol/L, provided the vitamin status of the study population is improved.