The Kastle-Meyer test is used for

• A. To confirm DNA presence.
• B. To presumptively identify blood based on hemoglobin's peroxidase-like activity.
• C. To detect semen via PSA.
• D. To identify if a stain is protein-based.

Answer: (B)

The test is a screening tool for blood that relies on the peroxidase-like activity of hemoglobin. When a stain containing blood is treated with a phenolphthalein indicator and hydrogen peroxide, the hemoglobin in the blood catalyzes a reaction that oxidizes the indicator, turning it pink. This color change indicates presumptive blood presence, giving investigators a quick signal to pursue further confirmatory testing. It’s not definitive identification of blood or its species, and substances with their own peroxidase activity (or strong oxidizers) can sometimes cause a false positive. It also won’t detect semen, DNA, or specifically identify the stain’s source. In practice, a positive Kastle-Meyer result leads to additional confirmatory tests to establish blood presence with greater certainty.