Whereas, SM provided a summative evaluation of method performance. The individual interpretation of bias and imprecision using FFP criteria allowed for the clear determination of the major source of error. There was some difference seen in interpretation for the other nine analytes. Comparing the quality processes eleven analytes produced a green light for both FFP and SM. The SM varied with analyte concentration with six analytes producing low Sigma values. Most analytes achieved at least minimum bias. The day-to-day imprecision of most tested analytes (except sodium and chloride) were smaller than the allowable imprecision (ranging from minimum to optimum). The outcomes of both quality approaches were then compared. The desirable total allowable error was determined from biological variation data and applied to the SM calculation. Biological variation data was used to calculate the minimum, desirable and optimal imprecision and bias for determination of FFP. Commercial external quality assurance (EQA) samples were used to determine the systematic error between the test method result and the instrument group mean result from the EQA program for each analyte. Third party commercial lyophilized internal quality control samples of human origin were used for day-to-day imprecision calculations. Twenty serum/plasma analytes were evaluated on the Beckman Coulter AU680. This study aimed to evaluate the imprecision and bias data generated for 20 routine chemistry analytes against both the biological variation fitness for purpose (FFP) and Sigma metrics (SM) criteria.
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