Forensic Serology: Color tests

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 • However it has been replaced by the Kastle-Meyer test because the benzidine has been identified as a known carcinogen (Can cause cancer)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

Results 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.

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

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

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?

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, fromhttp://www.bcps.org/offices/science/secondary/forensic/Bloodstain.pdf • Benzidine (CASRN 92-87-5). (n.d.). In EPA Integrated Risk Information System. Retrieved April 2, 2013, fromhttp://www.epa.gov/iris/subst/0135.htm • http://www.sciencebuddies.org/science-fair-projects/project_ideas/BioChem_p037.shtml#background • http://chemistry.about.com/od/homeexperiments/a/Kastle-Meyer-Test-To-Detect-Blood.htm • http://lem.ch.unito.it/didattica/infochimica/2006_Luminolo/determinazionesangue.html • http://www.susanmay.co.uk/student-report2.htm • http://viewfromwilmington.blogspot.com/2011/07/forensic-tests-for-presence-of-blood.html

Forensic Serology: Color tests