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Confirmatory Tests for Blood

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p244-245

2026-07-30

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Confirmatory Tests for Blood

Confirmatory tests for blood utilize the formation of crystals through the application of heat and testing chemicals. For example, the Takayama test (also known as the hemochromogen test) is performed by taking a small sample of the presumptive stain and placing it under a coverslip. The sample is heated briefly and, while being observed through a microscope, pyridine under alkaline conditions in the presence of a reducing sugar is added with a pipette. If blood is present, salmon-colored crystals form. The Takayama test is very sensitive, and even very old bloodstains may give a positive reaction. Heating the sample properly is key: Even when blood is present, improper heating of the sample can result in a false negative. Historically, the Teichmans test was used as a confirmatory test for blood; it is essentially the same procedure with different chemicals. A modification of the Takayama test appeared in the Journal of Forensic Sciences in 1993; the author, Hatch, used a reagent (dithiothreitol) to increase the rate of crystal formation (Hatch, 1993). Practically speaking, most forensic laboratories today do not conduct confirmatory tests for blood—the sample, if presumptively positive, will go straight to the DNA unit. A sensitive and simple test card (such as the ABAcard HemaTrace) is a cost-effective way to confirm blood on a stain too small for DNA analysis. Forensic laboratories are learning that it is simply not possible to send all potential evidence to the DNA unit; doing so creates the backlogs that currently burden those same laboratories. Some type of intelligent, evidence-based selection is necessary to route relevant evidence for the proper analyzes as well as determine which analysis should be conducted.