Alkaline phosphatase (ALP) is an enzyme that is released during bone growth; its levels generally peak by 18 years of age in women and by 19 in men and then decline with age. As reported in Analytical Chemistry, Halamek and his colleagues have successfully used the enzyme as a proxy for age. So far they have been able to predict, with about 99 percent accuracy, whether a mock blood sample spiked with varying concentrations of ALP hypothetically came from a healthy person who is older or younger than 18. Halamek is now trying to narrow the age range.

The study was small—involving fewer than 200 samples—and the technique has not yet been tried in a real-world setting. Plus, there are already (slower) DNA-based methods that can more precisely indicate a person’s age, says Manfred Kayser, a molecular biologist at the Erasmus MC medical center in the Netherlands. Ultimately, though, Halamek thinks his test could complement existing analyses and other types of evidence. He hopes these enzyme tests resemble point-of-care diagnostics that offer immediate results. Find high levels of ALP, he says, and investigators could quickly rule out an older suspect: “You can exclude a lot of samples so that they don’t need to go to the DNA lab.”