Not For the Squeamish! How Accurate is the Kastle-Meyer Blood Test?

Presenter(s)

Gwendolyn Hohl

Abstract or Description

This experiment aims to test the accuracy of the Kastle-Meyer blood test. This test is frequently used for blood at a crime scene due to its affordability, speed, and ease of use. However, it is estimated that approximately one-third of the test's positive results are false positives.  Peroxidases, such as those in potatoes, have been shown in studies to have the capacity to produce a false positive. Following research, a reasonable hypothesis would be that a positive sample was highly likely obtained from human blood, myoglobin-saturated water, and potatoes.

 To perform this experiment, safety gear must first be put on. Next, pour the substances into separate plates. Swab each substance with sterile cotton swabs. Add one drop of 70% ethanol and one drop of Kastle-Meyer reagent to the swab. If the swab turns pink immediately, the test detects a chemical oxidant and is contaminated; restart the process. If not, apply one drop of 3% hydrogen peroxide to the swab. The test is successful if the swab turns a vivid magenta color. The test is considered negative if there is no color change. Compare the outcomes after repeating this procedure with each substance.

After experimentation, the myoglobin-saturated water samples produced false positives, while potatoes produced a true negative. Two out of six samples were false positives: the bovine hemoglobin and porcine hemoglobin. 

In conclusion, the hypothesis was partially incorrect because potatoes had a negative result instead of a positive one, but myoglobin samples yielded false positive results.