The Kastle-Meyer test is an inexpensive, easy and reliable forensic method to detect the presence of blood. Here is how to perform the test.
- Kastle-Meyer solution (make this)
- 70% ethanol
- distilled or deionized water
- 3% hydrogen peroxide
- cotton swabs
- dropper or pipette
- sample of dried blood
Perform the Kastle-Meyer Blood Test
- Moisten a swab with water and touch it to a dried blood sample. You do not need to rub hard or coat the swab with the sample. You only need a small amount.
- Add a drop or two of 70% ethanol to the swab. You don't need to soak the swab. The alcohol does not participate in the reaction, but it does serve to expose hemoglobin in blood so that it can react more fully, to increase the sensitivity of the test.
- Add a drop or two of the Kastle-Meyer solution. This is a phenolphthalein solution, which should be colorless or pale yellow. If the solution is pink or if it turns pink when added to the swab, then the solution is old or oxidized and the test will not work! The swab should be uncolored or pale at this point. If it changed color, start again with fresh Kastle-Meyer solution.
- Add a drop or two of hydrogen peroxide solution. If the swab turns pink immediately, this is a positive test for blood. If the color does not change, the sample does not contain a detectable amount of blood. Note that the swab will change color, turning pink, after about 30 seconds, even if no blood is present. This is a result of hydrogen peroxide oxidizing the phenolphthalein in the indicator solution.