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COLLECTION OF BODY FLUIDS

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  P 239-240

2026-07-27

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COLLECTION OF BODY FLUIDS

Serological analysis, like other forensic analyzes, has two types of tests. The first is a presumptive test, which is highly sensitive to but not specific for a particular sub stance. For example, a color test may indicate that a stain may be blood, but not what kind of blood (human or nonhuman). It may even give a false positive result; that is, the substance may not be blood but something that reacts with the chemicals used in the test. The idea of presumptive tests is that some false positive results are acceptable as long as no false negative results are obtained. False negative results are possible, of course. The presumptive positive results can be more specifically tested with the second type of test, a confirmatory test, which tests positive for the substance in question and only that substance. Therefore, it is known in advance that some presumptive positive results will not be confirmed. Confirmatory tests lack sensitivity, in that a relatively large amount of the substance must be available for the test to be positive, but a few false negatives are acceptable as long as no false positives are obtained. Generally, confirmatory tests are performed in a laboratory rather than in the field because they require more controlled conditions and additional equipment than presumptive tests. The presumptive/confirmatory test structure allows crime scene and laboratory personnel to sort potential evidence into processing categories, such as “Test for DNA” and “No DNA Testing.” Because of the demands on reconstructive sciences to sort out what is relevant from what is irrelevant, a testing structure like this greatly aids the laboratory to more efficiently process and analyze evidence.