An evaluation of tetramethylbenzidine as a presumptive test for blood.

In forensic use, a presumptive test indicating the possible presence of blood is an invaluable tool. This type of test has particular value in screening out samples that are definitely not blood and do not require further testing. Used in this manner, a test should be sensitive to some component of blood which remains even after the blood has dried, aged, or become diluted. This ideal test should also be specific. No such ideal specific test actually exists; however, the tests that are currently used have been characterized, and remedies for nonspecific reactions have been devised (I). Since a presumptive test is used for screening, it should be simple to use and provide rapid results. Any test should be safe for the examiner applying it. Since its discovery in 1904 (2), benzidine has enjoyed both extremes of popularity and credibility. Early workers found benzidine to be a sensitive and specific test for blood. In time benzidine was discovered to be nonspecific for blood but specific for peroxidase. Because of its lack of specificity, man workers have discouraged its use [35]. In 1964, Culliford and Nickolls [1] published an in-depth review of the benzidine test. They found that false positives could be obtained from blood contamination, chemical oxidants, catalysts, and vegetable peroxidases. It was their contention that with a few precautions these interferences could be eliminated or explained. Because of Culliford and Nickolls’ work, the use of benzidine was bolstered. In 1975, the Forensic Science Foundation 6] reported in a study that 51% of 215 responding forensic laboratories used benzidine as at least one of their presumptive tests. The remaining 49% in the study were distributed among seven other color tests, indicating that benzidine enjoys a reasonably widespread use in forensic work. As a result of the sporadic popularity of benzidine and its dangers in use [7], other tests have been devised. Most, such as σ-tolidine has been reported to induce neoplasm [8]. Leucomalachite green and phenolphthalein are not true peroxidase tests but indicate the presence of a “nonspecific” oxidizing system [9]. Although benzidine is considered a hazardous substance, most serologists consider it too valuable to abandon. Benzidine was suggested as a possible carcinogen as early