ANALYTICAL GOALS DEVELOPED FROM THE INHERENT ERROR OF MEDICAL TESTS

Biological variation is inherent in all medical tests and is a major s ource of error in clinical test interpretation. We use inherent test e rror due to biological variability as the touchstone by which to valid ate the clinical acceptability of analytical goals. Analytical goals s hould consist of sets of complementary limits for total error, bias, a nd imprecision and a medical usefulness criterion (MUC) to ensure that the total error goal is met with stated certainty. We propose analyti cal goals that are limits for the total error of a measurement system, the joint capability of the process control prodecures and the measur ement process. Thus, the goals are the allowable analytical error for proficiency evaluation, internal process control, and the total error budget for design of method performance characteristics. We define MUC as the allowable maximum proportion of test diagnostic efficiency los t due to analytical error near medical decision points. MUCs <0.03 are not routinely clinically useful; MUCs >0.08 allow method performance characteristics that are undesirable for general clinical use. Using M UC = 0.05 and recommendations that imprecision not exceed one-half of the biological CV, we propose that fixed bias should not exceed one-fo urth to one-third of the intraindividual biological CV of the analyte and that total analytical error should not exceed 1.25 to 1.40 times t he biological CV. Modification of these analytical goals may arise for reasons of documented clinical practice or process stability. Our mod el quantifies in medical utility terms the results of such modificatio ns.