Presumptive Blood Testing and Blood Spatter

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Presumptive Blood Testing and Blood Spatter
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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.

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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

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Two Presumptive tests

• Kastle-Meyer (phenolphthalein)
• Luminol

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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

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KM cont

• Forms pink color if blood is present
• Sensitivity 110,000
• 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

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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

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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

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Luminol cont.

• Sensitivity 11,000,000
• 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.

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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.