How could you get a false positive test to indicate blood by using the Kastle-Meyer test?
False positive results may occur as powerful oxidising agents (for example, copper and iron salts) will turn the Kastle‐Meyer solution pink but this will happen before addition of the hydrogen peroxide.
What are disadvantages of Kastle-Meyer test?
Disadvantages – expensive, time-consuming 3. Testing crime scene samples for blood a. The Kastle-Meyer Test is a presumptive test for blood i.
How accurate is the Kastle-Meyer test?
Also according to the results presented here through the sensitivity test, the Kastle-Meyer Reagent was able to detect the presence of blood in the samples up to the dilution of 1:10,000 in human and dog, but not in 1: 100,000, as in previously described results, while cat blood was detectable up to a 1: 1,000 dilution …
What is considered a positive result for the Kastle-Meyer test?
A drop of phenolphthalein reagent is added to the sample, and after a few seconds, a drop of hydrogen peroxide is applied to the swab. If the swab turns pink rapidly, it is said to test presumptive positive for blood.
How sensitive is the Kastle-Meyer test?
During the direct tests, Kastle Meyer showed a higher sensitivity, detecting blood down to a dilution of 1:16,384, one order of magnitude lower than Hemastix.
Does a positive phenolphthalein Kastle-Meyer test prove that a stain is caused by human blood?
Other substances such as plant peroxidases and chemical oxidants may also cause a positive reaction. Therefore, a positive phenolphthalein test only indicates the presence of blood but does not confirm the presence of blood.
What is a common presumptive test for blood that can detect blood even if it is not visible to the naked eye?
Fluorescein is a presumptive blood test for latent bloodstain detection. It has been used in forensic applications to reveal trace amounts of blood. Traces of latent blood can be detected even after repeated cleansing of the crime scene.
Why is the Kastle-Meyer test presumptive?
Phenolphthalein reacts with hydrogen peroxide in the presence of hemoglobin to turn from colorless to pink. This reagents provide a presumptive test for blood, as food samples which contain hemoglobin (meat) and certain vegetables will also generate a positive response.
Is Kastle-Meyer a presumptive test?
Kastle Meyer and Hemastix reagents are presumptive tests commonly used in forensic casework for the detection of blood, and their suitability has been reviewed in numerous publications.
What might cause a false positive presumptive test?
What might cause a false positive presumptive test? A false positive presumptive test may be due to two or more non-coliform bacteria working synergistically to produce sufficient gas in the tube.
What is false positive presumptive test?
A presumptive test is a qualitative analysis that allows to identify, or confirm, the presence of a substance in a sample. These determinations usually occur, after a chemical reaction, and a specific colour is produced. A false positive is another substance reacting the same way, producing the expected result.
Why do blood contaminants give false positive result when used with the screening test for blood?
False- positive results may be due to the poor specificity of surrogate tests (e.g. pH, glucose) or, for culture-based tests, due to laboratory contamination of the culture system during handling.