Presumptive Blood Testing and Blood Spatter Presumptive tests for Blood • These tests are done on “reddish-brown” stains that are suspected to be blood • These tests are NOT admissible in court, but gives reason for further specific testing • In reports state either: – “the results indicated that there may have been blood present” or – “there was no indication given from the test results that blood was present” • Tests can give false positives and have different sensitivities. Blood info for testing • Refer to suspected blood as “reddish-brown stains,” even if presumptive test (PT) has been done. • Human blood has the following in red blood cells (RBC) that are specific to PT: – Hemoglobin • 4 proteins w/ Fe atom nestled in it • Responsible for O2 & CO2 transport • Human blood contains Fe which causes it to be red – Heme is the Fe component – Globin is the protein component Two Presumptive tests • Kastle-Meyer (phenolphthalein) • Luminol Kastle-Meyer (KM) • Contains: – Phenolphthalein, zinc, NaOH • Reacts with H2O2 – Which releases an oxygen radical in presence of heme – This oxidizes the KM • When KM is oxidized it turns pink KM cont • • • • • Forms pink color if blood is present Sensitivity 1:10,000 Highly specific (indicative) for blood This is an indirect test False positives from: – Some vegetative material such as potatoes, horseradish – Highly unlikely to have these in a scene which is why it is considered highly specific Process for KM • Place drop of dH2O on a cotton swab • Rub area being tested • Place a drop of ethanol on swab (“cleans sample”) • Place drop of KM solution on swab • Place drop of H2O2 on swab • If turns “hot” pink than it is positive for blood. If turns pink before H2O2 sample is contaminated Luminol • Contains (WI state crime lab formula): – 25 g Sodium carbonate – 0.5 g luminol – 555 mL dH2O – 100 mL H2O2 – H2O2 is added to solution right before using – Solution is good for about 1-2 hrs only • This is a chemiluminesence reaction • H2O2 releases radical O to react with Luminol Luminol cont. • • • • • Sensitivity 1:1,000,000 “glows” if blood is present Specificity: low This is a direct test False positives from: – Plant material containing chlorophyll, copper, brass, nickel salts, chrome fixtures, bleach, etc. Luminol procedure • Must be done in a dark location, get familiar with environment before spraying solution • Spray area to be tested • If blood is present it will cause luminol to glow. Need to photograph. Not long lasting.