Estimation of trueness of measurement results obtained in external quality assessment.

ABSTRACT

BACKGROUND: We demonstrated that lyophilised EQA/PT control materials, under certain circumstances, provide equal information about bias values as pools of native patient sera, and that in some cases, long-term reliable work with such materials is possible. METHODS: Bias values, estimated from results of routine surveys of EQA SEKK (Czech Republic) programmes for eight basic blood serum analytes using lyophilised control materials, were compared with bias values reached in the CAP (USA) programme where pools of native and lyophilised patient sera were used. RESULTS: Results for the components Na, K, Mg, Cl, P, urea, glucose, and uric acid were assessed. No significant differences were found between the bias values estimated by CAP using native sera, and those estimated by SEKK using lyophilised sera. CONCLUSIONS: It can be concluded that well-prepared lyophilised control materials may show the required commutability level. If so, they constitute a practical and cost-efficient alternative to native or fresh frozen sera when assessing bias.