Scientists at Erasmus University Medical Center in Rotterdam say as a forensic technique it could be used to revive police investigations that have hit a dead end, AAAS ScienceMag.org reported Monday.

The blood-age test relies on a peculiarity of T cells, immune cells in the body that recognize and fight microbial infections.

As T cells develop, they modify their DNA to recognize a wide variety of bacteria and other pathogens.

In the modification, some DNA is left over that is useless to the T cell, which discards it, researchers say.

The amount of discards in the body can be used to estimate a person's age since people produce fewer and fewer T cells as they get older.

"We take advantage of this waste product" in estimating a person's age from a sample of blood, forensic molecular biologist Manfred Kayser says.

The researchers found a correlation between the number of T cell DNA fragments and age, allowing them to pinpoint how old a person was to within plus or minus 9 years.

It's a wide range but enough to place suspects into generational categories, which could be helpful to police, Peter de Knijff, head of the forensic laboratory at Leiden University Medical Center in the Netherlands, says.

With this new test, de Knijff says, at least police can narrow down their suspect pool.

"This is the best we have right now," he says.

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