Clinical Chemistry, Vol 40, 1909-1914, Copyright © 1994 by American Association for Clinical Chemistry

Allowable imprecision for laboratory tests based on clinical and analytical test outcome criteria

JO Westgard, JJ Seehafer and PL Barry
Department of Pathology and Laboratory Medicine, Medical School, University of Wisconsin, Madison 53792.

The allowable imprecision for laboratory tests has been estimated from criteria based on clinical and analytical test outcome. The analytical outcome criteria studied are the Clinical Laboratory Improvement Amendments (CLIA) criteria for proficiency testing. The clinical outcome criteria are estimates of medically significant changes in test results taken from a study in the literature. The estimates of allowable imprecision were obtained from quality-planning models that relate test outcome criteria to the allowable amount of imprecision and inaccuracy and to the quality control that is necessary to assure achievement of the desired outcome criteria in routine operation. These operating specifications for imprecision are consistently more demanding (require lower CVs) than the medically useful CVs originally recommended in the literature because the latter do not properly consider within-subject biological variation. In comparing estimates of allowable imprecision, the CLIA outcome criteria are more demanding than the clinical outcome criteria for aspartate aminotransferase (asymptomatic patients), cholesterol, creatinine (asymptomatic patients), glucose, thyroxine, total protein, urea nitrogen, hematocrit, and prothrombin time. The clinical outcome criteria are more demanding for bilirubin (acute illness), iron, potassium, urea nitrogen (acute illness), and leukocyte count. The estimates of allowable imprecision from analytical and clinical outcome criteria overlap for aspartate aminotransferase (acute illness), bilirubin (asymptomatic patients), calcium, creatinine (acute illness), sodium, triglyceride, and hemoglobin.

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