Proposed and interim European quality specifications for imprecision and inaccuracy have been compared with the US CLIA total error criteria for proficiency testing (PT). To assess the relative demands of separate imprecision and inaccuracy specifications vs total error criteria, we derived the imprecision and inaccuracy that would be allowable if a testing process were to provide 90% assurance of achieving the analytical quality required by CLIA PT criteria. Charts of operating specifications (OPSpecs charts) were prepared for commonly used single-rule and multi-rule quality control procedures with 2 and 4 control measurements per run. Of the 23 tests studied, the proposed European specifications for imprecision and inaccuracy were more demanding than the CLIA requirements for 12 tests (albumin, alkaline phosphatase, amylase, calcium, chloride, creatinine, lactate dehydrogenase, lithium, magnesium, total protein, sodium, and thyroxine). The CLIA total error criteria were more demanding than the proposed European specifications for nine tests (alanine aminotransferase, aspartate aminotransferase, total bilirubin, cholesterol, creatine kinase, iron, triglycerides, uric acid, and urea nitrogen). Two tests (glucose, potassium) showed different requirements at different decision levels. Manufacturers and laboratory analysts need to compare these different quality specifications on a test-by-test basis to guide the development, selection, evaluation, and control of laboratory measurement procedures.
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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