Measurement uncertainty in clinical biochemistry

The definition of the term Measurement Uncertainty used in International Vocabulary of Basic and General Terms in Metrology is: A parameter associated with the result of a measurement, that characterises the dispersion of the values that could reasonably be attributed to the measurand. In simple terms it is how different a repeated laboratory result is from the first one. Different approaches are developed in the estimation of measurement uncertainty due to the many variables in clinical laboratories.The Modelling approach is that, uncertainty components include sampling, sample preparation, sample portion selection, calibrators, reference materials, input quantities, equipment used, environmental conditions, condition of the sample and changes of operator should be evaluated individually and combined as variances. The alternative approaches such as Single Laboratory Validation, Inter-Laboratory Validation, and Use of the External Quality Control Data use internal quality control charts and certified reference material or external quality control data..In our study we adopted Use of the External Quality Control Data approach and used internal and external quality control results of clinical chemistry and immunoassay tests for 2008, 2009, 2010. Combined Standart Uncertainty (Uc) is characterized by two parameters. The precision component is calculated by intralaboratory reproducibility and the bias is obtained from the deviation of assig0,ned value in external quality control program and the imprecision of the measurement on the peer group. Uc is multiplied by 1.96 to provide a level of confidence of approximately 95% which is called Expanded Uuncertainity (U).Although there is no demand from physicians and patients, laboratories should estimate their own measurement uncertainty in evaluating their perfomance and also in reaching a common solution.