Presumptive tests for blood play a critical role in the examination of physical evidence and in the determination of subsequent analysis. The catalytic power of hemoglobin allows colorimetric reactions employing phenolphthalein (Kastle-Meyer test) to indicate "whether" blood is present. Consequently, DNA profiles extracted from phenolphthalein-positive stains are presumed to be from blood on the evidentiary item and can lead to the identification of "whose" blood is present. Crushed nodules from a variety of legumes yielded phenolphthalein false-positive reactions that were indistinguishable from true bloodstains both in color quality and in developmental time frame. Clothing and other materials stained by nodules also yielded phenolphthalein false-positive reactivity for several years after nodule exposure. Nodules from leguminous plants contain a protein (leghemoglobin) which is structurally and functionally similar to hemoglobin. Testing of purified leghemoglobin confirmed this protein as a source of phenolphthalein reactivity. A scenario is presented showing how the presence of leghemoglobin from nodule staining can mislead investigators.
Keywords: CSF1PO; D13S317; D16S539; D18S51; D19S433; D21S11; D2S1338; D3S1358; D5S818; D7S820; D8S1179; DNA extraction; DNA typing; FGA; Hemastix; Kastle-Meyer; TH01; TPOX; amelogenin; blood test; bloodstain; capillary electrophoresis; false-positive; forensic science; hemoglobin; leghemoglobin; legume; phenolphthalein; polymerase chain reaction; presumptive; short tandem repeats; vWA.
© 2013 American Academy of Forensic Sciences.