Which of the following is the chemical method used to detect latent blood?

• A. Luminol
• B. Hemastix
• C. Fluorescein
• D. Luminal

Answer: (D)

The test relies on a chemiluminescent reaction. The reagent used is luminol. When luminol encounters the iron in hemoglobin and hydrogen peroxide, it is oxidized and emits a blue glow in the dark, revealing trace blood that isn’t visible to the naked eye. Luminal is an older brand name for luminol, which is why it might appear as an option, but the chemical name and the active method is luminol. Hemastix targets blood in urine, not latent blood on surfaces, and fluorescein relies on fluorescence rather than the chemiluminescent reaction luminol uses.