Detailed Procedure:

Any investigator working at a scene where blood or bodily fluids may be present should observe Universal Precautions. Please consult your laboratory for specific guidance on how to collect blood evidence based on the particular situation and the scene you are processing. General guidelines for collecting liquid blood, such as from a pool of blood, are as follows.

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To collect liquid blood:

1. Photograph the blood and its location. Photograph spatters, stains, and drops in both wide angle and closeup.

2. Wear new, unused, clean latex or nitrile gloves, respiratory, and eye protection.

3. A pool of wet blood on an immovable surface, like a tile floor, can be collected using an absorbent medium, such as a new, unused, clean sterile cotton gauze pad.

4. Open the gauze pad packaging and lay the pad on the pool of blood. Allow the pad time to absorb the blood.

5. If the pool is not sufficient for absorption onto a sterile cotton gauze pad, collect the stain using a new, unused, clean sterile cotton swab, rubbing it over the stain to remove as much of the blood as possible. Be sure to concentrate as much blood as possible on each swab (ie: two swabs with concentrated amounts of blood are better than six swabs slightly stained with blood).

6. Air dry the gauze pad or swab before packaging by laying it on a clean sheet of paper or hanging it up, at room temperature, away from direct heat, sunlight, or drafts. If blood evidence items are not dried before packaging, they may putrefy and therefore be unusable.

7. Once the sample is dry, place it in a new, clean evidence collection envelope. If swabs are being submitted, place them cotton tip first into the envelope. Seal the envelope with tape, not your saliva. Before inserting the item in the package, label the package with identifying information, including case number, date, exhibit number, a brief description, and your name. Initial and date the tape.

8. Submit a new, unused gauze pad or swab in a separate container as a control sample.

9. Store the item in a secure, temperature-controlled location, such as a refrigerator or climate-controlled evidence storage room, until you are able to transport it to the laboratory. Do not leave the swabs or any biological evidence in a hot car.

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If you are unsure how to collect this item, document the item photographically and contact your forensic laboratory for guidance before proceeding with collection procedures.

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Laboratory testing of blood:

Blood samples can be examined to possibly determine the nuclear DNA profile (sex is determined during the DNA analysis), species, blood type, and other characteristics of the donor. Comparison of questioned nuclear DNA profiles to known profiles is possible. Comparison of DNA to other samples via computerized database (eg: CODIS for DNA profiles) may be possible.

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Known blood samples:

Generally, known DNA is collected using a buccal swab. Please contact your forensic laboratory for assistance. A court order may be required to collect this type of sample.

 

Source:

CFITrainer.Net®. “Evidence Collection Toolbox.” Website, video, 2013.