Serology and Blood Analysis

What is Serology?

• Serology is the examination and analysis of body fluids

  • Including saliva, semen, urine, and blood

• From 1950 to the late 1980’s, forensic serology was a most important part of lab procedures

• BUT with the development of DNA techniques, significance was placed in developing DNA labs

• However, with limited funds and the time required for DNA testing, most labs still use many of the basic serology testing procedures when starting an investigation. 

Blood Characteristics

• Plasma is the fluid portion of the blood (55%)

• Cells (45%)

  • Erythrocytes are red blood cells. They are responsible for oxygen distribution

  • Leukocytes are the white blood cells; they are responsible for “cleaning” the system of foreign invaders

  • Thrombocytes or Platelets are responsible for blood clotting

• Serum is the liquid that separates from the blood when a clot is formed.

Blood Terminology

• ABO blood groups: based on having A, B, both or no antigens on red blood cells

• Rh factor: may be present on red blood cells; positive if present, negative if not

• Antigen: a substance that can stimulate the body to make antibodies. Certain antigens (proteins) found on the surface of red blood cells account for blood type.

• Antibody: a substance that reacts with an antigen

  • Type O has A and B antibodies and no antigens

  • Type A has B antibodies and A antigens

  • Type B have A antibodies and B antigens

  • Type AB has no antibodies but A and B antigens

• Agglutination: clumping of red blood cells; will result if blood types with different antigens are mixed. 

Population Distribution

Type O: 45%

Type A: 40%

Type B: 11%

Type AB: 4%

Paternity Testing

• Many cases of disputed paternity can be resolved when suspected parents and offspring are related according to their blood group systems

• Type O blood is considered a recessive gene

• Type A: AA or Ao

• Type B: BB or Bo

• Type AB: AB

• Type O: OO

Unknown Stain at a Scene

• Questions to be answered:

  • Is it blood?

  • Is it human blood?

  • Whose is it?

    • Determine blood type, alcohol content, drugs present, DNA analysis

  • How did it get there?

    • Determine the method(s) in which blood may have been deposited

Presumptive Test for Blood Determination

• Kastle-Meyer Color Test: a mixture of phenolphthalein and hydrogen peroxide; the hemoglobin will cause the formation of a deep pink color if the blood is present (presumptive test only)

• Hematest Test Strips: reacts with the heme group in the blood causing a blue green color

• Luminol Test: reaction with blood to produce light

  • Large areas can be quickly screened for blood by spraying luminol reagent

  • “Luminol test is extremely sensitive - it is capable of detecting blood stains that have been diluted up to 300,000 times.”

  • Does not interfere with subsequent DNA testing!

Animal vs. Human Blood

• Reptiles and Amphibians have larger nucleic red blood cells

• Mammals have no nucleus in RBC

• Precipitin Test - a precipitate forms

  • How is it made? 

    • Human blood is injected into a rabbit.

    • Antibodies are formed. The rabbit’s blood is extracted as a human antiserum

    • The antiserum is placed on the unknown blood. The sample will react with human proteins if human blood is present. A PRECIPITATE will form

    • This test is very sensitive and requires only a small amount of blood. 

DNA Analysis

• Since the 1990’s DNA has been replaced forensic reliance on blood factors (such as ABO) for the routine characterization of bloodstains

• DNA analysis gives extremely accurate individualization results.

• Only way to individualize it

Blood Spatter Evidence

• A field of forensic investigation which deals with the physical properties of blood and the patterns produced under different conditions as a result of various forces being applied to the blood. Blood, as a fluid, follows the laws of physics. 

Blood Droplet Characteristics

• A blood droplet will remain spherical in space until it collides with a surface

• A droplet falling from the same height, hitting the same surface at the same angle, will produce a stain with the same basic shape

Conditions Affecting Shape of Blood Droplet

• Volume of blood in the droplet

• Angle of impact

• Velocity at which the blood droplet left its origin

• Height

• Texture of the target surface

  • On clean glass or plastic: droplet will have smooth outside edges

  • On a rough surface: will produce spines on the edges of drop

Questions Answered by Blood Spatter Interpretation

• The distance between the target surface and the origin of blood

• The point(s) of origin of the blood

• Movement and direction of a person or an object

• The number of blows, shots, etc. causing the bloodshed and/or the dispersal of blood

• The position of the victim and/or object during bloodshed

Bloodshed Terminology

• Angle of Impact: angle at which blood strikes a target surface

• Drip Pattern: blood that indicated higher volume and deposition on vertical surface

• Cast-Off: blood that is thrown from an object in motion 

  • Removing a knife and blood flies off (usually on ceilings)

• Forward Spatter: blood that flows in the same direction as the force

• Back Spatter: blood that is direct back towards the source of energy

• Expirated Spatter: created by blood that is expelled from the mouth or nose from an injury - presence of oxygen in drops or lighter color can differentiate - can correlate with injuries sustained. 

  • Had air bubbles and looks different on a surface

• Contact Blood Stain: blood stains caused by contact between a wet clood-bearing surface and a second surface

  • Types:

    • Transfer: an image is recognizable and may be identifiable with a particular object

    • Swipe: wet blood is transferred to a surface which did not have blood on it

    • Wipe: a non-blood bearing object moves through a wet bloodstain, altering the appearance of the original stain

      • Can indicate that there is a struggle

• Directionality: relates to the direction of a drop of blood traveled in place from its points of origin

• Velocity:

  • High Velocity: greater than 25 feet per second, usually 100 feet per second; gives a fine mist appearance

  • Medium Velocity: 5 to 25 feet per second

  • Low Velocity: less than 5 feet per second

Bloodstain Patterns

• The shape of a blood drop:

  • Round: if it falls straight down at a 90 degree angle.

  • Elliptical: blood droplets elongated as the angle decreases from 90 to 0 degrees; the angle can be determined by a formula

• The pointed end of the blood stain faces the direction of travel

• The harder and less porous the surface, the less the blood drop will break apart.

Impact

• The more acute the angle of impact, the more elongated the stain

• 90 degree angles are perfectly round drops with 80 degree angles taking on more elliptical shapes

• At about 30 degrees the stain will begin to produce a tail

• The more acute the angle, the easier it is to determine the direction of travel. 

Area of Intersection and Convergence

• The location of the blood source can be determined by drawing lines from the various blood droplets to the point where they intersect.

• The area of convergence is the point of origin; the spot where the “blow” occurred. It may be established at the scene with measurements of angles by using strings. 

Blood Evidence

• Blood itself is class evidence and would include blood type. BUT, if you can determine the DNA you would have individual evidence.

• Blood stain patterns are considered class evidence in a courtroom. Experts could argue many points including direction of travel, height of the perpetrator, position of the victim, etc.