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Kastle Meyer (Km) Forensic Test For The Presence Of Blood

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Forensic science is one of the most important pillars used to understand the facts and events of crime, through the analysis of evidence in the crime scene and the re-creation of crime events that will help the crime investigators to solve there crime cases , through certain procedures of documentation and collection of materials available in the crime scene and through which are identified indications that can lead to arrest the perpetrator or to identify the victim or to know what happened at the crime scene. In this context we will focus on how we can detect a blood presence in the crime scene, this test will help to differentiate the blood from other substance which will save the time, effort and even the costs by transferring a lot of samples in to the lab to examine blood presence by using some tests at the crime scene which will indicate blood presence.

There are three commonly known tests that can be applied at the crime scene, the Leucomalachite Green (LMG), phenolphthalein Kastle Meyer (KM) and the Luminal test. Those three tests can give us a fast result of a blood presence at the crime scene. We will explore one of those methods that can be used at the crime scene in detail.

Kastle Meyer (KM) test

Kastle Meyer (KM) test is a quick, simple, reliable, and not expensive forensic test for the presence of blood, its sensitive, specific, and consume as little of the sample as possible. The 3-stage Kastle Meyer (KM) test has been used for decades as a rapid, presumptive test for blood. The test identifies the heme component of hemoglobin, which in the presence of hydrogen peroxide catalyzes the oxidation of the indicator phenolphthalein, turning it to pink.

Materials & Procedure: To apply the test some material must be provide as follows:

  • Kastle-Meyer solution
  • 70% ethanol
  • distilled or deionized water
  • 3% hydrogen peroxide
  • cotton swabs or filter paper
  • dropper or pipette.

Procedure

  1. Add a few drops of distilled water on the swap or filter paper and gently rubbed to the dry blood sample only small amount needed.
  2. After that use 2 drops of the 70% ethanol to the swap or filter paper to increase the sensitivity of the test no reaction will accord.
  3. Adding 1-2 drop of KM (phenolphthalein) solution it should be colorless or pale on the swap or filter paper at this stage.
  4. Adding 1-2 drops of 3% hydrogen peroxide solution in this stage the swap or filter paper must turn in to pink instantly which will indicate a positive test for blood presence. This chemical reaction can help to distinguish blood from other substance instantly.

False positive

For the KM test the result must show negative and positive, as we know by now if the sample turns in to pink color this will be an indication of blood presence therefore if the sample doesn’t show any change in color instantly this will mean that there is no blood is detected although if the sample will kept for approximately 30 second their will be a chainage in the color due the reaction even if no blood is present. This is a result of hydrogen peroxide oxidizing the phenolphthalein in the indicator solution. This test also will provide false positive result for example as we mentioned above if there is no blood the sample will turn in to pink after a while this is because of the chemical reaction of the presence of oxidizing and it can be found in broccoli or cauliflower this is an important fact should be putt in consideration of the forensic team at the crime scene. One important fact about the KM test it cannot differentiate between human molecules or animal it only detects blood presence of any kind.

The Kastle-Meyer blood test is an extremely sensitive test, the analysis of a wet or dry stain should have no impact on the sensitivity capable of detect blood dilutions as low as 1:107. If the test result is negative, it is reasonable proof that heme is absent in the sample. This can show how efficient and sanative the KM test.

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