New Forensic DNA Test Could Help Identify Semen Stains and Estimate a Donor's Age

Researchers in China have developed a DNA-based testing method that could help forensic investigators determine whether a biological stain contains semen and estimate the approximate age of the person who contributed it.

The study, published online on October 29, 2026, in Forensic Science International, was indexed in early November. It describes a combined testing approach designed to obtain two types of forensic information from the same DNA sample.

The research was conducted by scientists affiliated with Sichuan University and collaborating institutions.

Identifying the type of biological material recovered from a crime scene is an important part of forensic examination, particularly in sexual assault investigations.

However, determining that a stain contains semen does not establish the identity or age of the person who deposited it.

The researchers investigated whether DNA methylation could provide additional information.

DNA methylation refers to chemical modifications associated with DNA that can change with age and vary between different biological tissues. These patterns can help scientists estimate biological characteristics without determining a person's identity.

The team developed a multiplex SNaPshot assay containing seven age-associated CpG markers and two semen-specific markers.

CpG sites are locations in DNA where methylation patterns can be measured. By examining several markers simultaneously, the researchers aimed to identify semen and estimate donor age using a single analytical reaction.

The method was initially evaluated using 40 semen samples and 19 non-semen samples.

Researchers reported high specificity for semen identification within the tested samples, with the assay remaining effective using 50 nanograms of DNA.

They also evaluated five machine-learning models for age prediction.

The models were developed using a separate historical dataset containing 136 semen samples and independently tested against 34 samples with complete methylation profiles.

The best-performing model, a linear support vector machine, achieved a mean absolute deviation of approximately 4.65 years.

This means its age estimates differed from the donors' actual ages by an average of about 4.65 years in the evaluated samples.

The researchers also examined 20 simulated biological mixtures containing semen.

Only 12 mixtures met the study's semen-detection criteria. Age estimation in evaluable mixtures produced a larger mean absolute deviation of approximately 8.87 years.

These findings highlight an important limitation: mixed biological evidence can be more difficult to interpret than relatively clean laboratory samples.

For forensic investigators, the approach could eventually provide additional investigative clues when conventional DNA profiling does not produce an immediate identification.

However, estimating someone's age is not equivalent to identifying them. Prediction errors, sample degradation, biological mixtures, and population differences may affect reliability.

The researchers describe the method as a preliminary investigation, meaning further validation is necessary before its routine use in forensic casework.

The study illustrates how forensic genetics is moving beyond DNA identification toward extracting additional biological information from crime-scene evidence.