Utilization and yield of drug screening in the emergency department

Emergency qualitative tests for drugs are commonly ordered during evaluation of cases of suspected drug overdose. We prospectively compared the utilization and yield of drug screens based on urine and of identical tests of gastric contents under actual clinical conditions in a busy metropolitan emergency department. During the 4.5-month study period, physicians ordered drug screening in 405 of 582 (70%) study cases. Screens of both types of body fluid were ordered in only 95 cases (16%), suggesting study physicians regarded these tests to be functionally equivalent. Drug screens of gastric fluid were favored in cases involving acute ingestion and in medically complicated cases requiring gastric lavage. Urine drug screens were favored in clinically stable cases with primarily thought or behavior disorders. In the 95 cases for which both drug screens were ordered, gastric screens in 18 cases detected 20 drugs not detected by urine drug screening. Urine screening, on the other hand, identified 74 drugs not found on gastric screening in 48 cases. Gastric drug screening also performed poorly in comparison to quantitative serum drug levels. Seventeen false-positive urine or gastric screens were noted as well. Despite significant technical limitations, physicians frequently order drug screens in our emergency department. Qualitative drug screening of gastric fluid may prove useful in cases involving acute ingestion, but samples of urine and serum must also be submitted for analysis if optimal test performance is to be achieved.