A model for the evaluation of internal accuracy

Objective. To provide an evaluation model of internal accuracy illustrating its use in a quality control program of clinical chemistry. Methods. The m odel uses data transformed to percentage of assigned value (%AV) that allow s the pooling of different controls. Precision is evaluated by the mean of the intracontrol coefficients of variation, and accuracy by the mean of mea ns of the %VAs and its standard deviation. The model was used in 17,280 mea surements of 23 analytes assayed in seven pairs of controls (medium and hig h concentration) during four years in two automated clinical chemistry anal yzers. Results. The model established inaccuracy of 5% to 25% in seven anal ytes, five of them enzymes. It also detected interanalyzer differences in a ccuracy of five analytes (22%) and an erroneous assigned value in 19 of 304 controls (6%). Conclusions. The model showed its capacity to dissect the s ources of variation of accuracy. There was inaccuracy in 30% of the analyte s but further studies are needed to validate these inaccuracies with contro ls of other sources. The model can be useful for control programs of any qu antitative assay system. A summary description of the model's operation is given.