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To the Editor:—
Many clinical laboratory tests are not entirely specific and results may be pushed into an abnormal range by a variety of influences. The report of Fine and Kaplan (197:584, 1966) provides a reminder that the simple Watson-Schwartz reaction for porphobilinogen in urine is such a test. As the authors point out, a positive test for porphobilinogen should always be confirmed by butanol extraction.Patients today often are taking drugs which were unknown when now well-established laboratory tests were in the development stage. When these drugs, or their breakdown products, appear in the blood and urine specimens, results of the tests are sometimes altered.Our laboratory has observed abnormal reactions in several tests performed on the urines of patients taking meprobamate or drugs of the phenothiazine group. Of tests affected, the Watson-Schwartz reaction for porphobilinogen was the one most often requested. The observed color reaction was not
LaZerte GD. Porphobilinogen Tests and Drug Treatments. JAMA. 1966;198(5):564. doi:10.1001/jama.1966.03110180108038