Forensics Blood Analysis Test

serology

examination & analysis of body fluids

• used to be one of the most important forensics tool b4 DNA.

What specific fluids does Serology analyze?

Saliva, semen, urine, and blood.

What studies does serology include? (3)

Microscopy, toxicology, and spatter pattern analysis

serum

liquid that separates from clotted blood

2 parts of blood

Plasma and Cells

plasma

fluid portion of blood obtained by centrifuging a sample

• 55% of blood

cells

makes up 45% of blood

erythrocytes

red blood cells

leukocytes

white blood cells

thrombocytes

platelets

questions asked about an unknown stain (5)

• Is it blood?

• Is it human blood?

• Whose is it?

• Blood type, alcohol, drugs present

• Methods in which blood may have been deposited.

presumptive test

used to initially confirm if a stain is blood

• can be false positive, needs a confirmation test

What test is used for visible blood?

Kastle Meyer Color Test

Kastle Meyer Color Test

• Highly sensitive & can pick up traces of blood

• (some) Plant materials can give false positives

• Based on color change of phenolphthalein (yellow to pink) caused by hydrogen peroxide binding to iron in blood.

• Presence of blood —swab turns deep pink

What test is used for latent blood?

luminol

Luminol

• Very sensitive, can detect blood diluted up to 1 in 10k

• Can be used on old or degraded blood.

• Oxygen in RBCs react with Luminol —> glows

• Lot’s of false positives, especially with bleach.

2 ways to differentiate between Human and Animal Blood

• Microscopic observations

• Preciptin Test

Microscopic observation

Animal cells: larger cell, has a nucleus

Human cells: smaller cells w/out a nucleus

Precipitin Test

Animal serum and human antibodies are combined.

• Antiserum reacts with human protein

• small amount of blood needed bc test is sensitive

Karl Landsteiner

Discovered 4 types of blood based on presence or no presence of antigens on surface of RBC

Landsteiner & Weiner

Discovered the Rh factor while studying blood of Rhesus monkey.

breakdown of Rh positive across races

Caucasian: 85%

African American: 94%

Asian: 99%

antigens

a substance that stimulates the body to make antibodies

• antigens are proteins

• antigens on rbc’s membrane tells blood type

antibodies

substances that react with an antigen

ABO groups

based on having A, B, both, or no antigens on RBC.

Rh Factor

may be present on rbcs; positive if present, negative if not.

agglutination

blood clumping of RBCs that forms when you mix blood w/ different antigens.

Blood Type A (4)

Antigen: A

Antibody: B

Can give blood to: A or AB

Receives blood from: A or O

Blood Type B (4)

Antigen: B

Antibody: A

Can give blood to: B or AB

Receives blood from: B or O

Blood Type AB (4)

Antigen: AB

Antibody: none

Can give blood to: AB

Receives blood from: A, B, AB, or O

Blood Type O (4)

Antigen: None

Antibody: AB

Can give blood to: AB, A, B, O

Receives blood from: O

Rh Factor Positive

Antigen: D

Antibody: none

Can give blood to: +

Receives blood from: + or -

Rh Factor Negative

Antigen: none

Antibody: D

Can give blood to: + or -

Receives blood from: -

universal donor

O-negative

universal recipient

AB positive

Blood Spatter Analysis

A field of forensic investigation that deals w/ physical properties of blood and the patterns produced by the various of forces applied to it.

• blood follows laws of physics

blood droplet characteristics

• dropplet approx 0.05 mL

• remains spherical in space until it collides w/ a surface called target

• droplets that fall from the same height, hits the same surface at the same angle will produce stains w/ the same basic shape.

conditions that can affect blood shape (5)

• size of droplet

• angle of impact

• height

• velocity when the blood droplet left orgin

• texture of surface

droplets appear ___ on clean glass or plastic surfaces?

droplets will have smooth outside edges

droplets appear ___ on rough surfaces?

scalloping on the edges

what spatter analysis shows (6)

1. distance btwn target surface & origin of blood

2. points of orgin

3. movement and direction of person or obj

4. # of bullets/blows, causing bloodshed

5. type and direction of impact created by bloodshed

6. position of victim or object

angle of impact

angle at which blood strikes a target surface

bloodstain transfer

bloody object comes in contact w/ a surface and leaves a patterned blood image on the surface

cast-off

blood thrown from an object in motion

• usually straight

• spatter

backspatter

blood that is directed BACK towards the source of energy

frontsplatter

blood that is directed AWAY from source of energy

contact stain

bloodstains caused btwn a wet blood bearing surface and a second surface (may or may not have blood).

swipe

wet blood transferred to surface w/ no blood

• non-spatter

wipe

non-blood bearing obj moves through wet bloodstain, alters appearance of og stain.

high velocity

gives a fine mist appear (gun), greater than 25 ft per sec, usually 100 ft per sec

medium velocity

typically from blunt force/stabbing, 5-25 ft per second

low velocity

5 ft per second or less (blood dripping)

directionality

relates to the direction a drop of blood travels in space from its point of orgin

the direction of travel is in the direction of….

the tail

Round blood drop

Falls straight down from a 90* angle

Elliptical blood drop

blood drops elongate as the angle decreases from 90* to 0

impact angle formula

sin^-1(width/length) = impact angle

• always decimal, small/large

at what degree do blood drops take on eliptical shapes?

80 degrees

the more acute the angle of impact….

the more elongated the stain & easier to determine direction of travel

what degree does stains begin producing a tail?

30 degrees

area of intersection (AOI)

2-D spot on floor where blood drops intersect

area of convergence (AOC)

3-D point of origin where the “blow” occurred

• may be established at the scene by measuring angles w/ strings

how can aoc be established at the scene

measuring angles w/ strings

colored strings

can be attached to wall @ each blood drop to help determine position of victim

lasers

actual use is to reconstruct bullet trajectories, but can be used for blood spatters