A Study of the Sensitivity, Stability and Specificity of Phenolphthalein as an Indicator Test for Blood

Abstract

It has been known for many years that blood shows considerable peroxidase-like enzymic activity and therefore in the presence of hydrogen peroxide will give highly coloured products with certain substrates and, in particular, with amines such as benzidine. The carcinogenic nature of benzidine, however, dictates a search for a satisfactory alternative substrate such as Phenolphthalein which is believed to be non-carcinogenic. This study, designed to ascertain the relative merits of using benzidine and Phenolphthalein as reagents in indicator tests for blood, centres primarily on the sensitivity, stability and specificity of the two substrates. Despite the fact that the three-stage Phenolphthalein presumptive test for blood appears to be somewhat less sensitive than the conventional benzidine test, results indicate that it has several advantages in terms of specificity and stability. Results also indicate that the enzyme peroxidase, which is widely distributed in plants, does not contribute to false positive results in the three-stage Phenolphthalein indicator test for bloodstains.