Relevance of analytical and biological variations to quality and interpretation of test results: examples of application to haematology.
In the frame of a comprehensive quality system, the level of quality to be attained (analytical goals or quality specifications) need to be defined. Among the several approaches used for such a definition, that based on the (intra-individual) biological variation seems to be scientifically sound, and the most universally applicable. Data on biological variation are easily generated by applying specific experimental protocols. Once the biological variation is known, it can be combined to the analytical variation for the calculation of the critical difference. This is the difference between two repeated measurements in the same patient, due to the effect of both analytical and biological variation: when this difference is exceeded, a significant change in the patient's condition can be assumed. Some examples of calculation of the analytical goals and of the critical differences are shown, based on some quantities usually measured in the haematological laboratory.
Franzini
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Laboratorio di Chimica Clinica, Ospedale L, Sacco, Milan, Italy.
D000704:Analysis of Variance; D006403:Hematologic Tests / Q000592:standards* / Q000706:statistics & numerical data; D006801:Humans; D011786:Quality Control