Presumptive Blood Tests November 13, 2018

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?

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.

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

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).

Presumptive Blood Videos Kastle-Meyer https://www.youtube.com/watch?v=ZvhN9DDm9iI Luminol https://www.youtube.com/watch?v=u73H-5-RP5Y Bluestar https://www.youtube.com/watch?v=OB8G9T6JukM

Presumptive Blood Videos Fluorescein https://www.youtube.com/watch?v=ZS-UorKIfLU Hemestix: https://www.youtube.com/watch?v=k-ur9TSKSaw (tetramethylbenzideine) KM; LG; TB: (7 minutes 40 seconds) Blood Evidence collection https://www.youtube.com/watch?v=pnH2HnB-GrI

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?

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

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

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?