There is insufficient experimental data about bias for serum cholesterol measurements. In 1986, "standard" (lyophilized) external quality assessment/proficiency testing (EQA/PT) control materials and frozen mixtures of native patient sera were sent simultaneously to routine clinical US laboratories. The differences between results depended on the reagents and equipment used, and ranged from -8.8% to +4.4%. In addition, some analytical systems did not find any difference at all between the "standard" and native control materials. The authors considered the differences that were observed to be caused by the influence of the matrix of the "standard" EQA/PT control materials (1).
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