1. Presumptive Blood Tests
November 15, 2018

2. Forensic Characterization of Bloodstains
What three questions need to be answered by the criminalist when examining dried blood?
Is it blood?
Is it human blood?
How closely can it be associated with a certain individual?

3. What is a Presumptive Blood Test?
A presumptive blood test would indicate the presence of blood at the crime scene using color tests, fluorescence, and microcrystalline tests.

4. Presumptive Blood Tests
Color Tests – Chemical reactions that cause a color change.
Kastle-Meyer Test (pink)
Leucomalachite Green (green)
Tetramethyl benzidene (blue-green)
Fluorescence-Chemical reaction that gives off energy in the form of light.
Luminol
Bluestar
Fluorescein
Alternative Light Sources – Different wavelengths of light will reveal different components.
Microcrystalline tests – the addition of chemicals to the blood that form characteristic crystals containing hemoglobin

5. Hemoglobin
Hemoglobin (Hb) a protein found within the red blood cells (Erythrocytes).
Its main function is to carry oxygen throughout the body.
Hemoglobin contains four iron (Fe) containing heme groups.
Hemoglobin has peroxidase-like activity. This means that it can accelerate the oxidation (loss of electron) of chemicals in the presence of peroxides (Ex: Hydrogen Peroxide (H2O2).

6. Presumptive Blood Videos
Kastle-Meyer
Luminol
Bluestar

7. Presumptive Blood Videos
Fluorescein
Hemestix:
(tetramethylbenzideine)
KM; LG; TB: (7 minutes 40 seconds) Blood Evidence collection

8. Task: Presumptive Blood Tests
What is the chemical reaction involved to produce the observed reaction?
What is the limitation for this method?
What are the advantages?

9. What a positive test looks like What a negative test looks like
What it looks like
How it works
What a positive test looks like
What a negative test looks like
Advantage
Disadvantages
Other (ie. Examples, sensitivity, etc)
Alternative Light Sources
UV or violet light (absorption)
blood absorbs UV or violet light (black light)
dark relative to the background
no change
Some visibility, easy
Does not fluoresce at visible wavelengths
Luminol
C8H7O3N3
chemiluminescent: electron in the oxygen atom is boosted to higher energy orbitals
glows
does not glow
Very sensitive, non-destructive in aqueous solutions, can be used with PCR
Low selectivity
(w/Cu, metals, bleach, food items test positive), can interfere with some older serological tests
sensitive - 1: 108
Fluorescein
C20H12O5
Absorbs at 445 nm (indigo) and fluoresces at 520 nm ( green)
fluorescence
no fluorescence
better than luminol when bleach is present
less sensitive than luminol, subject to false positives like luminol
sensitivity - 1: 104; only used if luminol doesn't give useable results

10. alkaline phenophthalein and hydrogen peroxide
What it looks like
How it works
What a positive test looks like
What a negative test looks like
Advantages
Disadvantages
Other (ie. Examples, sensitivity, etc)
Kastle Meyer Test
alkaline phenophthalein and hydrogen peroxide
reacts with the heme group in blood to turn the stain pink (oxidation reaction)
bright pink
yellow or colorless
low cost; can be run 2 ways: one is more selective, one is more sensitive
false positives from horseradish, potato or other vegetable peroxidases and Vit C
Leucomalachite Green
LMG and hydrogen peroxide
LMG reacts with the heme group in blood to turn the stain blue green
blue green
colorless
Vitamin C doesn't interfere as much
Less sensitive than KM; false positives from vegetable peroxidases
Tetramethyl benzidene
3,3'5,5'-tetramethylbenzidine
TMB + diisopropylbenzene dihydroperoxide
orange to green to blue (highest blood concentration
More convenient than KM
More expensive than KM
Hemastix detects blood in urine; forensic labs use Hematest tablets

11. Define a presumptive test. Where in the blood is hemoglobin found?
Presumptive Blood Test Lab Analysis Questions:
Define a presumptive test.
Where in the blood is hemoglobin found?
Break down the word hemoglobin, what is heme and what is globin?
What does the heme react with in order to give a positive result to the Hematest?
What chemical reaction takes place to cause a positive Kastle-Meyer test?
If an investigator receives a positive result to a Kastle-Meyer test, can they guarantee that blood is present? Why or why not?
How do investigators find blood stains that are not immediately visible under normal lighting?
What pieces of evidence tested positive for blood?