A new forensic blood test could allow law enforcement to determine whether blood at a crime scene came from a minor or an adult and how recently the person parted with it (Anal. Chem. 2016, DOI: 10.1021/acs.analchem.6b01169). Jan Halámek of the University at Albany, SUNY, and colleagues focused on alkaline phosphatase (ALP), an enzyme that hits peak levels in the blood during adolescence before decreasing sharply around age 17 for females and 18 for males. The researchers tested 100 samples of human serum spiked with randomly generated concentrations of ALP chosen to match natural enzyme levels found in juveniles and adults. The team determined the ALP concentrations with a known assay that is catalyzed by the enzyme: the conversion of p-nitrophenyl phosphate to p-nitrophenol, a yellow compound that can be measured using spectrophotometry. A statistical test on the measurements revealed that the assay had a 99% probability of differentiating young males from older ones and a 100% probability of differentiating young females from older ones, even after the samples sat on a lab bench near a window for 48 hours to simulate crime scene conditions. The researchers also developed a model based on ALP activity to predict how long blood has been at a crime scene.