Equations were derived during an eight-month period and later validated twice in the same setting. There were 6,570 electrolyte and blood cell profile panels ordered during the equation derivation period. Except for two equations involving abnormalities with very low prevalences, the equations were also well calibrated. Prior results for the abnormality being considered were the strongest predictors, followed by other laboratory results, diagnoses, and the physicians' estimate of the probability that the test would be abnormal. Clinical data can accurately predict abnormal results of common outpatient laboratory tests.
Computers can help find the necessary data and produce estimates of risk.