Forensic serology color tests
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Forensic Serology: Color tests. By: Mike O'neill Mazin Osman Claudia Palma Adam Ramirez. Color Tests. Determination of blood are made by conducting color tests The Benzidine test was the most commonly used for many years.

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Forensic Serology: Color tests

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Forensic Serology:

Color tests

By: Mike O'neill

Mazin Osman

Claudia Palma

Adam Ramirez

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  • However it has been replaced by the Kastle-Meyer test because the benzidine has been identified as a known carcinogen (Can cause cancer)

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

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.

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

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


Blood may be present, but is too dilute to react

False Negative

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

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

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.


  • 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

Strength and Weaknesses


  • Easy to use

  • Can be used on the field easily


  • Not as accurate as the Kastle-Meyer or Benzidine tests

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.

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, 1992 in connection with the murder of Hilda Marchbank

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.

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?


  • 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 92-87-5). (n.d.). In EPA Integrated Risk Information System. Retrieved April 2, 2013, from






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