Agreement between laboratory tests and self-reports of alcohol, tobacco, caffeine, marijuana and other drug use in post-partum women.

The agreement between self-reported consumption of several drugs and laboratory tests used to detect their use is examined. Post-partum women (N = 108) enrolled in a research study participated in a detailed interview covering alcohol and caffeine ingestion, tobacco smoking and use of marijuana and other psychoactive drugs. They also kept a 4-day record of their use of these substances. Blood and urine samples were taken and a physical exam done at the close of the record period. Laboratory tests to detect use of alcohol, tobacco, caffeine, marijuana and other drugs were carried out and the results compared to self-reported drug use in the interview and the record. The degree of agreement depended on the drug taken, the test used and the pattern of drug use in the sample. Sporadic or infrequent consumption related poorly to laboratory tests, especially those that were designed as screening tools. Regular consumption could be identified with greater accuracy. However, the group associations evident between self-reports of drug use and laboratory results were not sufficient to guarantee that subjects were correctly classified. Error in both self-report and the decision made from laboratory values must be taken into account in determining the confidence that should be placed in the data and the conclusions drawn from it.