Forensic Serology Test

Serology

Study of the body fluids

Which body fluids contain serum?

Blood

Saliva

Semen

plasma

Liquid part of the blood composed water, trace minerals, several proteins, and antibodies

ABO identity

Typing of whole blood

Which two blood antiserums are needed in determining blood type?

Anti-A

Anti-B

How is the ABO blood group determined?

The reaction of Anti-A and Anti-B with specific blood antigens

Blood Type A

42%

Antigens on Erythrocytes (Agglutinogens) -- A

Antibodies in Plasma (Agglutinins) -- Anti-B

Can Give Blood To -- A, AB

Can Receive Blood From -- O, A

Blood Type B

10%

Antigens on Erythrocytes (Agglutinogens) -- B

Antibodies in Plasma (Agglutinins) -- Anti-A

Can Give Blood To -- B, AB

Can Receive Blood From -- O, B

Blood Type AB

3%

Antigens on Erythrocytes (Agglutinogens) -- A and B

Antibodies in Plasma (Agglutinins) -- Neither Anti-A/Anti-B

Can Give Blood To -- AB

Can Receive Blood From -- O, A, B, AB

Blood Type O

45% -- most common

Antigens on Erythrocytes (Agglutinogens) -- Neither A or B

Antibodies in Plasma (Agglutinins) -- Both Anti-A & Anti-B

Can Give Blood To -- O, A, B, AB

Can Receive Blood From -- O

Rh Factor

Landsteiner discovered this in blood, labeling it Rh+ if the antigen was present in the red blood cells and Rh- if it was not

What questions must the forensic scientist answer when examining dried blood?

1. Is it blood?

2. Is it human blood? animal blood?

3. Whose blood is it?

What are the presumptive tests made whenever a blood-like stain is found at the scene of a crime?

1. Color Tests -- Kastle-Meyer test & Leucomalachite (Hemastix) test

2. Fluorescent Chemical test -- Luminol

Kastle-Meyer test

When blood, hydrogen peroxide and phenolphthalein are mixed together, a dark pink color results. Color change is due to the hemoglobin causing a chemical reaction between the hydrogen peroxide and phenolphtalein

Luminol

The reaction with blood causes a glow; it is a highly sensitive chemical that is capable of presumptively detecting bloodstains diluted up to 300,000 times

Precipitin test

Used to determine if a confirmed blood stain is of human or animal origin; when animals are injected with human blood, antibodies form that react with the invading human blood to neutralize its presence; these antibodies can be recovered from the human anti-serum; any kind of animal antiserum can be produced in this way

SENSITIVE TEST -- 10-15 year old blood stains can give positive results

Bloodstain Pattern Analysis

Examination of the shape, distribution, appearance, and location of bloodstains and spatters

Categories of Bloodstain

1. Passive Bloodstains

2. Transfer Bloodstains

3. Projected Bloodstains

Passive Bloodstains

Drops created or formed by the force of gravity acting alone; includes drip tails and flow patterns, clots and blood pools

Transfer Bloodstains

Created when a wet, bloody surface comes in contact with a secondary surface; a recognizable image of all or a portion of the original surface may be observed in the pattern; includes smudges, swipes, smears

Projected Bloodstains

Created when an exposed blood source is subjected to an action or force greater than the force of gravity; the size, shape, and number of resulting stains will depend primarily on the amount of force used to strike the blood source

Types of Projected Bloodstains

Arterial spurts/gushes

Cast-off Stains

Impact Spatters

Arterial spurts/gushes

Bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery

Cast-off Stains

Blood released or thrown from a blood-bearing object in motion

Impact Spatters

Bloodstain patterns created when a blood source receives a blow or force resulting in the random dispersion of smaller drops of blood; the greater the force, the smaller the diameter of the blood drops in the pattern

Types of Impact Spatters

Low Velocity Impact Spatter

Medium Velocity Impact Spatter

High Velocity Impact Spatter

Low Velocity Impact Spatter

The majority of the spatters are large and circular with diameters of 4 mm or larger

Medium Velocity Impact Spatter

Usually seen in blunt force or stabbings; the diameters of the spatters are 2 mm - 4 mm

High Velocity Impact Spatter

Impact spatter that measures less than 2 mm in diameter (mist-like appearance); usually associated with gunshots, explosions, and high speed collisions

Factors Affecting the Appearance of Blood Drops

Height

Target Surface

Angle of Impact

Height

Size of the blood drop is related to the distance fallen; as the height increases, the diameter of the blood drop increases; after 7 feet, all blood drops of equal volume will look the same since there is no change in air resistance

Target Surface

Smooth, hard, and less porous surfaces (like glass and glazed tile) produce smooth edged drops with less spattering; Rough, more porous surfaces (like wood, paper, concrete) produce drops that are irregular in shape with more spattering

Angle of Impact

Acute angle formed between the direction of the blood drop and the surface which it strikes; vertical drops are circular (90 degrees); as it decreases, the shape of the blood drop becomes more elongated and develops a "tail"

Tail

Points in the direction that the blood has traveled, but is not included in the length measurement

Area of Convergence

- Location where blood drops meet by drawing a line through all the drops away from the direction of travel (2D)

- Determines the source of the blood or the spot where the victim was struck

Point of Origin

Determined mathematically or by stringing (for each blood drop, a string can be guided back to the point); use the area of convergence and the angle of impact of each blood stain

Height = Distance x tangent of angle of impact

Blood

- Can be distinguished as to human or animal

- DNA analysis can provide individual identification