Commutability of control materials in cholesterol measurement

Abstract

Franzini C, Luraschi P. Commutability of control materials in cholesterol measurement. Scand J Clin Lab Invest 1993; 53: 51-55.The 'commutability' is the property of a material to show inter-assay changes comparable to those of patients' sera. In order to assess the commutability, the cholesterol concentration was measured in 107 patients' sera and in 24 lyophilized control materials by a direct enzymatic method and by a reference-class procedure. The distance from the regression line of patients' sera results, expressed in SD units (normalized residual), was calculated and used to assess the commutability of each material. Out of 24 materials tested one had a normalized residual outside the ±3 interval (–4.4), and was considered as non-commutable. However, the distribution of the normalized residuals from the remaining 23 materials suggested a different behaviour in comparison with patients' sera, in the specific pair of methods. The relevance of this finding to the control of accuracy is discussed.