Accuracy and comparability of long-term measurements of cholesterol.

Laboratories of the Lipid Research Clinics Program (LRC) maintained the accuracy of their measurements of total cholesterol by using seven pooled serum calibrators supplied by the Centers for Disease Control (CDC). Over the 11-year life of the LRC, each calibrator was prepared in succession and a target value was assigned by the CDC reference method for cholesterol. The results of a special experiment in which six of the seven calibrators were analyzed simultaneously demonstrated that the target values were accurately assigned. Deviations of the target values from the experimental means ranged from zero to 1.7% of the original target value. The experiment revealed no evidence of drift in the bias of the reference method over the life of LRC and demonstrated the accuracy, consistency, and the comparability of the values assigned to the successive calibrator pools used by the LRC laboratories during more than eight years. It demonstrated the reliability of a reference method and the suitability of frozen serum pools for maintaining an accurate measurement base for serum cholesterol.