Periodic verification of results' comparability between several analyzers: experience in the application of the EP31-A-IR guideline.

Objectives: To assess the usefulness of the EP31-A-IR guideline published by the Clinical and Laboratory Standards Institute (CLSI) to perform the periodic verification of results' comparability between several analyzers.

Methods: Twenty-four biochemistry parameters that could be measured in different analyzers were included: albumin, alkaline phosphatase, alanine aminotransferase, amylase, aspartate aminotransferase, calcium, chloride, C-reactive protein, creatine kinase, creatinine, direct bilirubin, gamma glutamyl transferase, glucose, lactate dehydrogenase, magnesium, phosphate, potassium, sodium, total bilirubin, total cholesterol, total protein, triglycerides, urea and uric acid. In accordance with the EP31-A-IR guideline: (1) Patient samples were selected considering the concentration or activity of interest. (2) Acceptance criteria were established specifically for each concentration or activity level. A quality specification based on biological variation or on state of the art was selected, considering the analytical performance of the available technology. (3) Maximum allowable differences (MAD) between analyzers were calculated. (4) Measurements were performed as stated in appendix B of the guideline. (5) Maximum differences between analyzers were calculated. Results were considered comparable when the maximum difference was less than or equal to the MAD.

Results: For the 24 parameters evaluated, any difference between analyzers exceeded the MAD.

Conclusions: The EP31-A-IR guideline proved to be useful for periodic verification of results' comparability. However, it must be considered that, to be practicable, it may require to adjust the acceptance criteria in accordance to the analytical performance of the available technology; as well as the number of analytical measurements conforming to the laboratory resources.