Dating Your Blood

The CSI franchise makes it seem like detectives only need a few drops of blood, some saliva, or a strand of hair to close a murder investigation within 24 hours. Some of the techniques on the shows do not exist—or if they do, it takes weeks, not minutes, to get results. But many of these fantasies are tools investigators dream of using, and scientists continue to search for new ways to solve crimes using DNA evidence. Researchers at Erasmus MC University Medical Center Rotterdam in the Netherlands were able to determine a person’s age by running a DNA test on a drop of blood.

Investigator Manfred Kayser designed a test that looks for spliced remnants of T cells in the blood. When bacteria or viruses invade a body, the immune system triggers T cells in the blood. As the T cells activate, they produce small, spherical cells called signal joint TCR excision circles (sjTRECs). Researchers know that sjTRECs decrease at a constant rate each year, making easy to quantify age.

Kayser analyzed 200 blood samples from infants to 80-year-olds.

Using florescent DNA, which binds to sjTRECs, Kayser determined the amount of sjTRECs in the blood, estimating a person’s age within nine years. He notes that this test worked just as accurately on samples, which sat in storage for a year, meaning this could be an affective tool in reducing cold case backlogs. This test is one of the most accurate phenotypic DNA tests. The other frequently noted phenotypic test determines whether a person’s eye color is blue or brown, but is far less accurate.

And while guessing an age within nine years may not seem accurate enough, it can be useful to investigators who have no information about suspects.