Semen test is a sensitive rapid test for the qualitative detection of human PSA in vaginal samples and in liquids or stains suspected of containing semen. PSA-based testing can detect even small concentrations of human PSA, including traces found on textiles and other materials.
The test can be used to examine suspected traces in connection with sexual offence investigations or suspected infidelity. The result indicates whether PSA has been detected in the sample, which suggests the presence of semen. However, the test does not show who the semen came from, how it came into contact with the material or when the stain was formed.
What does the semen test detect?
PSA, or prostate-specific antigen, is a protein produced by the prostate gland. It occurs in high concentrations in human semen. Small amounts of PSA may also occur in other body fluids, but their concentrations are generally considerably lower.
The semen test is based on monoclonal antibodies that react with human PSA. The test has a detection limit of 4 ng/ml PSA, making it sensitive to small PSA concentrations.
What is the semen test used for?
The semen test can be used to detect PSA in samples suspected of containing human semen. It has been used to examine samples associated with suspected sexual offences and in investigations of suspected infidelity.
Suspected stains may be found on underwear, bed sheets or other textiles. A small amount of material from the stain is mixed with water and then examined with the test strip in accordance with the instructions supplied with the product.
A positive result means that PSA has been detected in the sample, which suggests the presence of semen. The result does not identify who the semen came from, explain how it came into contact with the material or indicate whether sexual activity was consensual or forced.
What samples can be examined?
According to the product information, the test can be used with vaginal samples and suspected liquid or stain samples.
- Vaginal samples
- Suspected liquid samples
- Dried stains
- Underwear
- Bed sheets and other bedding
- Other textiles and materials with suspected stains
Dried semen may, in some circumstances, still be detected several weeks after the incident. The ability to detect PSA is affected by factors such as the amount of sample, the material, storage conditions and whether the textile has been washed or cleaned.
How to use the semen test
The test and sample should be brought to a temperature of approximately 15–30 °C before testing. Prepare the sample according to the instructions supplied with the product.
- Prepare the sample in a clean container.
- Remove the test strip from its sealed pouch.
- Immerse the test strip vertically in the sample liquid for 10–15 seconds.
- Do not allow the liquid to rise above the MAX line.
- Remove the strip and place it on a clean, level surface.
- Read the result after 5 minutes.
Do not interpret the result after 10 minutes. For best results, the test should be performed within one hour of preparing the sample.
How to interpret the result
Positive result
Two coloured lines appear: a control line at C and a test line at T. A faint test line should also be interpreted as positive. A positive result means that PSA has been detected in the sample at or above the test’s detection limit.
Negative result
Only the control line at C appears. No test line appears at T. This means that PSA has not been detected at or above the test’s detection limit.
Invalid result
If no control line appears at C, the result is invalid. Repeat the test using a new test strip.
What does a positive result mean?
A positive result shows that human PSA has been detected in the examined sample. This suggests that the sample contains semen.
The test does not show who the semen came from and cannot link the sample to a particular person. It also cannot establish when the stain was formed, how the semen came into contact with the material or whether sexual activity was consensual or forced.
How should the test be stored?
Store the test in its sealed pouch at 2–30 °C. Do not freeze the test and do not use it after the expiry date.
Important information in cases of suspected sexual offences
If rape or another sexual offence is suspected, the police or healthcare services should be contacted as soon as possible. Washing, changing clothes and handling suspected evidence should, where possible, be avoided before professional evidence collection has taken place.
More information about reporting a crime and the support available can be found on the Finnish Police website.
Frequently asked questions about the semen test
What is a semen test?
A semen test is a rapid test that detects human PSA in a sample. PSA occurs in high concentrations in human semen and is therefore used as a marker when examining suspected semen stains.
How sensitive is the semen test?
The test has a detection limit of 4 ng/ml PSA. This means that it can detect small concentrations of human PSA in the examined sample.
Can the test be used on dried stains?
Yes. Suspected dried stains on underwear, bed sheets and other textiles can be used as sample material when the sample is prepared according to the instructions.
Can semen be detected several weeks later?
Yes. Dried semen may, in some cases, still be detected several weeks after the incident. Detection is affected by the amount of sample, the material, storage conditions and any washing or cleaning.
How quickly is the result available?
The result is read after 5 minutes. The result must not be interpreted after 10 minutes.
Can the test show who the semen came from?
No. The test only shows whether human PSA has been detected in the sample, which suggests the presence of semen. It cannot identify who the semen came from or link the sample to a particular person.
Can the test prove infidelity or a sexual offence?
No. A positive result only shows that PSA has been detected in the sample, which suggests the presence of semen. It does not show how or when the semen came into contact with the sample, who it came from or whether sexual activity was consensual or forced.
