Blood analysis has long been one of the forensic scientist's most important tools. Now, a new blood test being developed by Igor Lednev and colleagues at the University of Albany promises to determine the age of a victim or suspect from samples taken from a crime scene within an hour.

Without blood, the detective's life would be a lot harder. Since the average person carries around 4.7 to 5.5 liters (1.2 to 1.5 gal) of blood, it tends to get splashed around crime scenes a lot when violence is involved. Though distressing, it's also a great help because blood is a veritable treasure trove of information. From the way its splattered or sprayed about an area, an examiner can deduce a great deal about the events that took place, cause of death, and about the suspect, if any.

Back in the lab, the blood can tell even more. It can show whether the blood is human, the race and sex of the suspect or victim, state of intoxication or drug use, general health, and (if a matching sample is in a database) provide a positive ID as definitive as fingerprints.

Unfortunately, one thing that blood doesn't like to give up is the age of the person, which can be vital in many cases to gain a conviction or free the innocent. This is because to determine a person's age, you need to have something that changes predictably over time.

The best example and the most widely used technique is to look at the teeth and bones of a person. The development of the teeth, how they have worn, and their pathology can tell a lot about a person's age. Bones, too, tell their story as autopsy and X-rays can determine the growth of bones, how they have fused as a person grows and matures, and how their environment affects them.

Blood, on the other hand, is a bit more tricky. What Lednev and his team were looking for was something in human blood that changes as a person ages and can be identified and quantified in the lab in a very short time. What they settled on was hemoglobin – the painfully complex protein molecule found in red corpuscles that transports oxygen throughout the body and gives blood its distinctive red color. But what interested the scientists is the fact that hemoglobin changes as a person grows older.

The team's new technique relies on Raman spectroscopy, where a sample of blood is illuminated by a laser beam, causing the atoms in the sample to shift to different energy states. As they revert to normal, the electromagnetic radiation they give off allows the investigator to determine the composition and structure of the molecules.

Specifically, the team was looking for molecular subunits in two types of hemoglobin – fetal hemoglobin (HbF), which is found in newborns, and adult hemoglobin (HbA). As a person grows older, the ratio of HbF to HbA grows smaller, so the researchers took samples from volunteers in three age groups – infants, adolescents, and adults. These were then subjected to Raman spectroscopy and the ratio of HbF to HbA in red blood cells per 100 ml of blood was measured.

So far, the team has been able to correctly place the adult and adolescent samples with an accuracy of 99 percent and the infants with 100 percent. One advantage was that the process is not only fast, but non-destructive. Also, no sample preparation was required, meaning it could be used in the field along with more conventional tests.

The next step will be to refine the test in hopes that it will be able to narrow down the results to more exact ages.

The research was published in ACS Central Science.