Processing
PRESUMPTIVE BLOOD TESTS
Presumptive blood tests can be used to determine the possible presence of blood. Most presumptive blood tests indicate the possible presence of blood with a color change when blood and an oxidizer are present. All of the presumptive tests below utilize the heme portion of the hemoglobin molecule in blood.
Phenolphthalein (Kastle Meyer) Presumptive Blood Test
This test will produce a positive result for both animal and human blood.
Prior to using the chemicals, test the kit using a positive control (human bloodstain) and a negative control (sterile, clean swab) to ensure that the chemicals are working properly.
For indirect testing – use a sterile cotton swab or piece of filter paper (slightly moistened with distilled water for dry stains) to collect a sample of the suspected bloodstain.
For direct testing – cut away a very small piece of the stain.
Add a drop of the Phenolphthalein Working Solution to the swab, filter paper or cutting.
Add a drop of the Hydrogen Peroxide to the swab, filter paper or cutting.
A rapidly appearing pink color will indicate the presumptive positive presence of blood. If there is not an immediate color change, this indicates a negative result.
o-Tolidine Presumptive Blood Test
This test will produce a positive result for both animal and human blood.
Prior to using the chemicals, test the kit using a positive control (human bloodstain) and a negative control (sterile, clean swab) to ensure that the chemicals are working properly.
For indirect testing – use a sterile cotton swab or piece of filter paper (slightly moistened with distilled water for dry stains) to collect a sample of the suspected bloodstain.
For direct testing – cut away a very small piece of the stain.
Add a drop of the o-Tolidine Working Solution to the swab, filter paper or cutting.
Add a drop of the Hydrogen Peroxide to the swab, filter paper or cutting.
A rapidly appearing blue-green color will indicate the presumptive positive presence of blood. If there is not an immediate color change, this indicates a negative result.
Heme Stix Presumptive Blood Test
This test will produce a positive result for both animal and human blood.
For indirect testing – use a sterile cotton swab (slightly moistened with distilled water for dry stains) to collect a sample of the suspected bloodstain.
For direct testing – cut away a very small piece of the stain.
Remove the cap from the Heme Stix tube. Insert the head of the swab into the tube. Break off and leave the head of the swab inside the tube and remove the remainder of the stick. If using a cutting, drop the entire cutting into the tube.
Squeeze the outside of the Heme Stix tube to break the vial containing the brown solution. Allow the solution to coat the swab or cutting.
Reinsert the cap with the second vial attached to it into the Heme Stix tube. Squeeze the exterior of the Heme Stix tube to break the second vial which contains the clear liquid.
A rapidly appearing blue-green color will indicate a presumptive positive presence of blood. If there is not an immediate color change, this indicates a negative result.
Leucomalachite Green Presumptive Blood Test
This test will produce a positive result for both animal and human blood.
Prior to using the chemicals, test the kit using a positive control (human bloodstain) and a negative control (sterile, clean swab) to ensure that the chemicals are working properly.
For indirect testing – use a sterile cotton swab or piece of filter paper (slightly moistened with distilled water for dry stains) to collect a sample of the suspected bloodstain.
For direct testing – cut away a very small piece of the stain.
Add a drop of the Leucomalachite Green Working Solution to the swab, filter paper or cutting.
Add a drop of the Hydrogen Peroxide to the swab, filter paper or cutting.
A rapidly appearing blue-green color will indicate the presumptive positive presence of blood. If there is not an immediate color change, this indicates a negative result.
Hexagon OBTI Presumptive Blood Test
This test is specific to human blood. So if it is important to differentiate between possible animal blood and human blood, this test should be used.
Open the collection tube that is provided with the kit and use the attached applicator to scrape a small amount of sample into the collection tube.
Replace the cap on the tube and gently shake the tube gently to mix the collected sample with the tube’s buffer solution.
Add three drops of the buffer and stain solution from the collection tube into the sample window on the test strip.
The liquid sample will move across the test strip, passing the letters “C” and “T”. If a line appears at “C”, this means that the test has performed properly. If a line appears at “T”, this means that the sample has tested positive for the presumptive presence of human blood.
- Presumptive blood tests are sensitive, but not necessarily specific.
- Any color changes that occur before the addition of peroxide may indicate the presence of a chemical oxidant.
- A positive color alone should not be interpreted as proof that a stain is blood.
- False positives can result from the presence of copper salts, nickel salts, and vegetable peroxidases.