Which test is used to indicate prior blood presence even after cleanup in a crime scene?

• A. Luminol testing
• B. Kastle-Meyer test
• C. Hemastix
• D. Phenolphthalein test

Answer: (A)

Detecting trace blood after cleanup relies on a test that generates light in the presence of heme. Luminol reacts with the iron in hemoglobin and, in a darkened area, emits a chemiluminescent glow. That glow reveals faint or wiped-away bloodstains that aren’t visible to the naked eye, making it ideal for indicating prior blood presence even after cleanup. It’s extremely sensitive and can be used on a variety of surfaces, guiding investigators to where blood residues remain so they can collect confirmatory samples. Keep in mind it isn’t confirmatory by itself, but it points to locations for further testing. The other options are less suited for this purpose: Kastle-Meyer changes color with the presence of blood but relies on visible residues and can be affected by cleaners or other substances; Hemastix is designed for detecting blood in urine, not surface traces; phenolphthalein is an older presumptive test that can yield false positives and is less reliable for uncovering faint, washed traces.