Routine laboratory testing for medical disorders in psychiatric inpatients.

We examined the clinical utility of routine admission laboratory testing for medical disorders in 250 psychiatric inpatients by using clinical criteria to classify laboratory abnormalities as true- or false-positive results. The mean number of tests per patient was 27.7. The mean percentage of true-positive results was 1.8%; the mean predictive value was 12%. When three clinically defined subgroups were examined, both measures of test performance varied in direct proportion to the pretest probability of medical disease. Eleven patients (4%) had important medical problems discovered through routine laboratory testing. A testing battery consisting of nine tests in women and 13 in men would have identified all of these patients. Our results suggest that extensive, routine testing for medical disorders in this setting is unnecessary and that more efficient and accurate testing strategies, based on clinical information, can and should be developed.