Transcript Presumptive Testing and Blood Spatter

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
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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.
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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.