Points to consider when conducting DNA analysis from semen.

When performing DNA analysis from semen, there are a number of important precautions that must be taken in order to increase the reliability and accuracy of the results. Semen is a suitable sample for DNA analysis, but if care is not taken in the collection method, storage and handling, the DNA may deteriorate, making accurate analysis impossible.

The following section details the precautions to be taken when carrying out DNA testing from semen.

1. Accurate collection of samples

Prevent contamination: when collecting semen, it is important to avoid contamination from other substances (e.g. blood, saliva, skin cells) and the environment. This requires ensuring that the containers and utensils to which the sample is attached are clean.
Suitable quantity: it is recommended that as sufficient a quantity of semen as possible be collected. Smaller quantities can be used for DNA testing, but the greater the quantity, the greater the accuracy for detecting DNA.
Correct labelling: once the sample has been taken, it must be labelled correctly to prevent misidentification. It is important to clearly state who collected the sample, the date and time, and the type of sample.

2. How to store the samples

Prompt processing: ideally, the collected semen sample should be sent to the agency performing the DNA analysis as soon as possible. Over time, the DNA may deteriorate, reducing the accuracy of the analysis.
Appropriate storage temperature: if time is required for appraisal, it is recommended that samples are kept refrigerated. For long-term storage, frozen storage below -20°C is recommended. DNA may be degraded if left in high temperatures or high humidity.

3. Handling of samples

Avoid direct contact: when collecting semen samples, it is important that hands and other objects do not touch the sample. Contamination with another person’s DNA may result in inaccurate results.
Use of disposable tools: it is recommended that disposable containers and tools for taking samples are used and kept clean. Reusable containers and tools must be rigorously disinfected.

4. Note sample deterioration

DNA degradation over time: semen contains DNA, which naturally degrades over time.In particular, prolonged exposure to the open air or exposure to high temperatures and humidity causes DNA to degrade more quickly, so it is important that it is promptly sent for appraisal or stored appropriately.
Chemical effects: if semen comes into contact with chemicals such as detergents or disinfectants, DNA may be damaged, which can negatively affect the results of the identification. It is recommended that semen samples are handled in a chemical-free environment.

5. Where there is a mixture of several DNAs.

Risk of mixed samples: the identification of samples can be complicated if the DNA of more than one person is mixed, e.g. in cases of sexual contact.In such cases, it is important to inform the agency carrying out the analysis in advance that the samples may be mixed.
Difficulty of analysis: mixed samples require a high degree of skill and experience for appraisal. It is important to choose a reliable appraisal institute.

6. Points to note in legal proceedings

Semen samples as evidence: the use of semen samples as evidence in legal proceedings requires proper storage and handling of evidence; if DNA results are used in court, the entire process from sample collection to identification must be strictly controlled.
Use a reliable appraisal institute: for appraisal results to be recognised as legally valid, they must be carried out by an accredited institute.In Japan, an appraisal body must meet specific criteria if it is to be used as evidence in a court of law.

7. Factors affecting appraisal results.

Sample quantity and quality: having a sufficient quantity of semen sample will increase the accuracy of the assay, but even small quantities can be assayed with proper processing.Conversely, deterioration or contamination increases the risk of inaccurate results.
Sample condition: if the semen sample collected is fresh and properly stored, the accuracy of the identification will be improved.On the other hand, dried semen or samples that have been aged for some time can make DNA extraction more difficult.

Summary

When performing DNA identification from semen, proper collection and storage of the sample and prevention of contamination are of paramount importance.Semen can be a very reliable DNA sample, but improper handling can lead to inaccurate results.Preventing sample deterioration and contamination and ensuring that the sample is handled by a reputable laboratory is key to obtaining accurate and reliable test results.They must also be handled in accordance with evidence preservation and legally authorised procedures when relevant to legal proceedings.