Collection and Storage DNA Evidence

Each year, Genetic Technologies, Inc. successfully analyzes several cases from evidence vaults dating back to the early 1970's. Investigators and others gathering DNA evidence should do so with great care, utilizing the following guidelines.

DNA, in a dry state, is very stable. Ultra-violet light, extreme heat and high humidity are the primary destructive agents of the DNA molecule. There are a few basic rules that must be followed for the proper collection, packaging and storage of DNA evidence.

Stains (Wet) - Blood, Semen, Saliva
Biological evidence should always be allowed to air-dry before packaging/storage. Moisture allows bacterial growth to occur, rapidly destroying nuclear material and therefore, greatly diminishing the possibility of obtaining useful DNA results. Blow dryers and/or other heating devices should not be used to force the item into a dry state.

Wearing non-powdered gloves, lay the item flat on a clean surface, isolated from a high traffic area, or place in a clean paper bag and allow drying for several hours. Powdered gloves may leave a residue on evidentiary material, which may interfere with DNA analysis.

If the item cannot be packaged, due to size or other constraints, disinfect a pair of scissors with a 5% bleach solution and cut out as much of the stained area as possible. In order to avoid contamination issues, gloves should be changed in between handling or seizing each piece of evidence and scissors should be disinfected in between cutting each new stain.

Each piece of evidence/stain should be packaged separately. The cutting should be placed in a clean envelope, paper bag or cardboard box to air-dry. Plastic bags should NOT be used for storing wet evidence, as they do not allow moisture to evaporate.

Pooled, Liquid Blood, Saliva or Semen
When dealing with blood, saliva or semen in a pooled or liquid state, swab as much of the sample as possible onto sterile cotton swabs and allow the swabs to air-dry. Package swabs in clean paper envelopes.

Tubes of Blood, Tissue Samples, Body Remains
Tubes of blood drawn intravenously must be refrigerated, NOT frozen! Tubes of blood will break upon freezing, resulting in a biohazard condition in addition to the potential contamination of other evidentiary material. The blood should be removed from the tube and placed on an appropriate storage substrate as soon as possible. Tissue samples removed during surgery, autopsy, etc. should NOT be fixed in formalin. Formalin and Formaldehyde will interfere with traditional RFLP DNA analysis. PCR DNA analysis is successful in the presence of these fixative reagents, however it is best not to store tissue samples requiring DNA testing in either solution. Tissue samples should be placed in sterile, plastic containers and should be frozen as soon as possible. They may be shipped overnight with cold packs or on dry ice.

Stains (Dry) - Blood, Semen or Saliva
For the best possible results, an item that has biological evidence deposited on it should be submitted in its entirety. Each item should be placed in a separate, clean paper bag, cardboard box or plastic bag (if entirely dry). If the item cannot be submitted in its entirety and a cutting cannot be taken, the following methods of collection may be used.

Place two or three drops of distilled water or physiological saline (0.85%) onto a sterile, cotton swab and rub over the stained area, transferring as much of the stained substance as possible onto the swab. Allow the swab(s) to air-dry and package in clean paper envelopes.

Dried samples may be scraped with a sterile scalpel or disinfected knife blade onto a clean square of paper or glassine paper. The scraping method of collection may result in a significant loss of sample, as the substance subjected to scraping will flake and disperse as very fine particulate matter. The paper should be folded on all edges in order to keep the scrapings from falling out. The folded paper should be placed inside a clean paper envelope and sealed.

Properly collected, stored, and shipped biological specimens for DNA analysis help assure robust results. Specimens in a dry state will offer ample genetic evidence for decades.