Chapter 17: Identification of Urine, Sweat, Fecal Matter, and Vomitus

Urine identification begins with understanding the physiological processes underlying urine formation within the nephron system, which enables forensic scientists to target specific urine components through presumptive testing. High concentrations of urea are detected using DMAC reagent or urease-based assays, while creatinine presence is confirmed through the Jaffe reaction, a colorimetric test sensitive to this kidney metabolite. Confirmatory testing proceeds to more specific markers such as Tamm-Horsfall protein, also known as uromucoid, and 17-ketosteroids, which definitively establish urine as the biological source. Sweat analysis leverages immunological and RNA-based methodologies to identify perspiration-specific proteins, particularly dermcidin, a peptide produced by eccrine sweat glands that serves as a reliable confirmatory marker. Fecal matter examination combines macroscopic and microscopic observation with chemical presumptive assays targeting urobilinoids through fluorescence-based detection methods. Contemporary fecal identification increasingly utilizes DNA analysis of fecal bacterial communities, particularly targeting genes associated with Bacteroides species, which constitute a significant portion of gastrointestinal microbiota and provide genus-level confirmation. Vomitus and gastric fluid identification depends on detecting proteolytic enzymes characteristic of gastric secretion, with pepsin serving as the primary target. Pepsin, a protease responsible for protein digestion in the stomach, can be identified through enzyme-based assays that confirm the presence of gastric contents. Collectively, these analytical approaches enable forensic professionals to distinguish between biological fluids and materials that may otherwise appear similar, providing crucial probative value in casework by establishing biological source material and linking evidence to specific bodily systems or functions.