Factors Affecting the Results of Serum Cholesterol Determinations: An Interlaboratory Evaluation

We present results of an interlaboratory survey of cholesterol assays in which methodology, standardization technique, type of standard, reagent source, and control sera used are considered. Each of these factors is evaluated, on both clear and icteric sera, with respect to accuracy, interlaboratory precision, and associated random error. We find that most participants use direct techniques, that these laboratories do not use correction procedures where these are needed, and that not all extractants effectively prevent bilirubin interference. Our data illustrate that precision on clear sera is best by direct procedures, but not in the presence of bilirubin. Participants uniformly exhibit better intralaboratory precision than interlaboratory agreement, regardless of the variable being studied. It is appropriate to consider the interactions of variables if a technique is to be properly evaluated.