Unit 7B The Forensics of Blood

How many and what are the different presumptive tests?

1. Kastle Meyers

2. Hemastix

3. Luminol

4. Fluorescein

5. Leuco Crystal Violet (LCV)

What three questions will be asked if investigators find a red substance?

1. Is it blood?

2. is the blood human or animal

3. Who does the blood belong to?

What test will be asked if investigators try to figure out if a red substance is blood?

Kastle Meyers Test

What test will be asked if investigators try to figure out if if the blood is human or animal?

Precipitin Test

What test will be asked if investigators try to figure out who the blood belongs to?

Blood Typing and DNA fingerprinting

Presumptive tests have reagents that react with what in blood?

Properties of hemoglobin in blood

What is Kastle Meyers reagent?

Phenolphthalein

What will Kastle Meyers react with?

Hemoglobin

What color does Kastle Meyers produce a positive result?

Pink

What is a setback for the Kastle Meyers test?

It can produce false positives because other substances that aren’t blood can catalyze (speed up reaction) to produce a false positive

What is Hemastix reagent?

Tetramethylbenzidine (TMB)

What will Hemastix react with?

Hemoglobin

What color does Hemastix produce a positive result?

Green or blue green color

What is Luminol reagent?

Luminol solution

What will Luminol react with?

Hemoglobin, iron present in blood, metals, paints, cleaning products, plant materials

What color does Luminol produce a positive result?

Blue luminescence

Why would Luminol be used?

To find blood that would be cleaned or removed

What are two setbacks for Luminol?

1. Other substances react with the luminol solution like metals, paints, cleaning products, and plant materials

2. The chemical reaction can destroy other evidence in the crime scene

What is Fluorescein reagent?

Fluorescein solution

What will Fluorescein react with?

Hemoglobin

What color does Fluorescein produce a positive result?

Greenish-white or yellow

Why would Fluorescein be used?

To detect old or latent blood in a crime scene

What is the purpose of Leuco Crystal Violet (LCV)?

Blood enhancement to get blood to be more visible to be analyzed and photographed

What does Leuco Crystal Violet (LCV) react with?

Hemoglobin

What color does Leuco Crystal Violet (LCV) produce a positive result?

Bluish-purple

What are three reasons why a presumptive test produces a false positive?

1. Adding hydrogen before phenolphthalein

2. Other substances can catalyze (speed up the reaction to make it look positive) the reaction

3. Contamination 

What test will be used after investigators find out a substance is blood?

Precipitin Test

What is the Precipitin test?

Anti-human antibodies will be added to the red substance, if the substance agglutinates that means there is a presence of human proteins on the surface of red blood cells. 

What two tests will be used after investigators determine if a substance is blood and if they determine if the blood is human?

DNA Fingerprinting and Blood Typing

What is DNA Fingerprinting?

Gel electrophoresis to separate samples size and charge to compare samples to find a match (I think)

What is blood typing?

Add specific antibodies to a unknown blood sample if it agglutinates that means that is the blood type 

For example- if you add A antibodies to a blood sample and it agglutinates that means it is blood type A