1. Forensic Serology: Color tests
By: Mike O'neill
Mazin Osman
Claudia Palma
Adam Ramirez

2. Color Tests Determination of blood are made by conducting color tests
The Benzidine test was the most commonly used for many years.
However it has been replaced by the Kastle- Meyer test because the benzidine has been identified as a known carcinogen (Can cause cancer)

3. Color Tests
The Benzidine and Kastle-Meyer color tests are based on the observation that hemoglobin possesses peroxidase-like activity
Hemoglobin- A red blood cell protein that transports oxygen in the bloodstream; it is responsible for the red color of blood
Peroxidases are enzymes that accelerate the oxidation of several classes of organic compounds when combined with peroxides

4. Kastle-Meyer Test
The Kastle-Meyer test relies on the iron in hemoglobin to promote the oxidation of phenolphthalin to phenolphthalein.
Phenolphthalin is colorless, but in the presence of blood and hydrogen peroxide, it changes to phenolphthalein, which makes the solution pink.

5. Sensitivity and Limitations
It is extremely sensitive
Capable of detect blood dilutions as low as 1x10^7
If the test result is negative, heme might be absent in the sample
The test will give a false positive result in the presence of any oxidizing agent like cauliflower or broccoli

6. Performing The Kastle-Meyer Test
Collect a sample of the blood using a cotton swab (if the blood is dry, water could be used to moisten the swab)
Add two drops of 70% ethanol to the swab (Helps increase the sensitivity of the test)
Add a drop or two of the Kastle-Meyer solution
Add two drops of hydrogen peroxide solution

7. Results Pink Color Develops Results Interpretation
After Kastle-Meyer is applied
False Positive
The reaction did not occur as the result of blood’s presence
After hydrogen peroxide is applied
Positive
blood is indicated
Never
Negative
Blood is not indicated (may not be present)
False Negative
Blood may be present, but is too dilute to react

8. Benzidine Color Test
The benzidine color test was, for many years, the most popular type of preliminary blood test.
In 1988, however, benzidine was identified as a carcinogen and since then its use has mostly been discontinued.
Benzidine + Blood Stain + Hydrogen Peroxide = Pink Color

9. Strengths of Benzidine
It was a common test for blood.
It is a presumptive test for identifying Blood
An enzyme in blood causes the benzidine to be oxidized to a polymer
which is blue colored. This makes it very easy to find the result

10. Weaknesses of Benzidine
This test is very unreliable. Although a test may appear that it has been positive, the substance that was found due to the color presence may not be the actual substance that was involved.
It is a carcinogen which has been used as part of a test for cyanide and also in the synthesis of dyes. It has been linked to bladder cancer and pancreatic cancer.
It is highly sensitive.

11. Hemastix Presumptive field test for blood
Designed as a dipstick test for blood
Involves moistening a strip in distilled water and then placing it into contact with a suspect blood stain
If the strip appears to turn green, it is positive for blood

12. Strength and Weaknesses
Strengths:
Easy to use
Can be used on the field easily
Weaknesses:
Not as accurate as the Kastle-Meyer or Benzidine tests

13. Susan May Case
On March 12, 1992, Susan May was visiting her aunt Hilda Marchbank. She arrived at the house at approximately 9:30 am and discovered Hilda dead on her bed. She was savagely beaten on her head and face and was smothered with a pillow.

14. Susan May Case
Investigators found a number of stains that appeared as blood on the walls of the scene.
The Kastle-Meyer tests was performed to indicate whether it was blood or not
Some of the stains contained Susan May's blood
Susan May was arrested on March 30, in connection with the murder of Hilda Marchbank

15. Meredith Kercher Case
Meredith Kercher was found dead in the bedroom of her apartment in Perugia, Italy. She had several stab wounds in her throat.
The Kastle-Meyer test was performed on a substance that appeared to be blood and came back positive.
However, this could have been wrong because the pink color could have been caused by reagents used in fingerprint analysis.

16. Review Questions What are color tests used for?
What are the three tests mentioned in this presentation?
What color does a positive Kastle-Meyer tests turn?
What is one
What color does the Benzidine test turn?
Why was the Benzidine test discontinued?
What color does a hemastix strip turn if it is positive for blood?

17. Sources
Saferstein, R. (2011). Forensic Science - An Introduction (Second ed., p. 293). Upper Saddle River, NJ: Pearson Prentice Hall.
Bloodstains. (n.d.). Retrieved April 2, 2013, from
Benzidine (CASRN ). (n.d.). In EPA Integrated Risk Information System. Retrieved April 2, 2013, from
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