Serology

Chapter 13

Forensic Serology: Examination and identification of body fluids at a crime scene.

Includes blood, saliva, seminal fluid, vaginal secretions, urine, feces, and tissues.

What is Blood?

Blood is a connective tissue with blood cells that are suspended in a liquid.

How much blood does the average contain?

Females = 4 – 5 liters

Males = 5 – 6 liters

Blood makes up about 8% of your total body weight.

Blood is composed of a living portion and a non-living portion.

Living

Non-living

Plasma – yellowish liquid in which blood is suspended.

Plasma consists of 91% water, 7% proteins and 2% other substances!

Red Blood Cells (Erythrocytes)

Carries O₂ to the body’s cells.

Hemoglobin can bind to CO₂ but most CO₂ is carried in the plasma.

As they develop

Make up about 95% of the living portion of the blood.

they lose their nucleus and most of their cell organelles.

Iron is necessary for oxygen transport and 2/3 of body’s iron is in the hemoglobin.

Erythrocytes are 700 times more numerous than white blood cells and 17 times more numerous than platelets.

RBC’s live for about 120 days in males and 110 days in females.

They are broken down in the liver and spleen.

White Blood Cells (Leukocytes)

They are larger than red blood cells but fewer in number.

Has nuclei and cell organelles

Purpose is to fight disease.

There are different types of leukocytes.

They can move out of blood vessels and into tissues when needed.

Platelets – pieces of cytoplasm with a cell membrane.

Clotting factors cause threadlike substances which trap cells to stop bleeding.

Platelets help form blood clots.

Karl Landsteiner won the Nobel Prize for discovering the different types of blood in the ABO system.

Red blood cells have markers on them called antigens.

4 different blood types

White

African-American

Type O (47%)

Type A (41%)

Type B (9%)

Type AB (3%)

Type O (46%)

Type A (27%)

Type B (20%)

Type AB (7%)

Blood type is considered to be class evidence.

Plasma includes proteins called antibodies.

Antibodies can only attach with a specific antigen and this is known as agglutination.

When the wrong type of blood is introduced into the body the antibodies will cling to the antigens and agglutination will occur.

Agglutination is the clumping together of cells.

ABO Blood Types

There is also two Rh groups (Rh positive and Rh negative).

You are Rh-positive if you have Rh antigens on the surface of your cells.

85% of Caucasians and 95% of African-Americans are Rh-positive.

ABO Blood Types and Rh Factors

Protocols for chemical analysis of blood:

1. Preliminary physical examination to spot potential evidence

2. Recording of evidence and the exact location (Photos and videotaping)

3. Preliminary screening tests – presumption tests

4. Specific confirmatory tests

Preliminary Blood Tests

Luminol

Chemiluminescence – emits own light

Blue to yellow-green color is shown in the presence of blood

Color appears immediately & lasts for at least 30 seconds

Does not affect DNA testing

Outline of Body

Footprint

Shoe print

Luminol

Fluorescein

Also emits its own light

Applied with hydrogen peroxide

Shine a strong short-wave light to induce fluorescence

Added thickening agent allows it to be used on vertical surfaces

Fluorescein does not interfere with DNA typing

Luminol and fluorescein are not specific only for blood.

They can give false positives in the presence of certain vegetable extracts.

Kastle-Meyer test is a field presumptive test for blood.

Kastle-Meyer Test

Combines phenolphthalein and hydrogen peroxide.

Turns a vivid fuchcia or pink color in the presence of hemoglobin.

Kastle-Meyer Test

Confirmatory tests

The Teichmann and Takayama tests are the most popular confirmatory test.

A crystallizing reagent is added to the blood and distinct shaped crystals form.

Takayama Test

Blood must be determined if it is human.

Can be determined by the immunoprecipitation type tests.

Human blood is injected into a rabbit, which produces antibodies to human blood. The rabbit blood is then an antiserum.

There will be a reaction between any anti-human antibodies in the antiserum and the antigen in the blood.

The reaction will leave a precipitin ring on the test tube.

Ouchterlony Test

Antigens and antibodies diffuse through a gel towards each other.

They form a brownish precipitate where they meet.

If there is not precipitation then the blood is not human.

The Hexagon OBTI

When blood in the well mixes with the reagent it will migrate up the strip to where the anti-human antibodies are and forms a blue line if positive.

The control line is blue.

Blood has a higher surface tension so it does not act the same as water.

Tends to adhere to external surfaces and only spreads when enough external forces overcome the surface tension.

Blood is viscous and flows more slowly than water.

Bloodstains are divided into 3 categories:

Passive

Spatter

Altered

Refer to the table at the bottom of page 310.

Blood dropping straight down is will form a circular pattern.

The size of a blood drop depends on how large the surface from which it falls is. The larger the surface, the larger the droplet.

The longer the distance of the fall, the greater the diameter of the splatter.

The greatest acceleration rate of blood is called the terminal velocity (about 25 ft./sec for a drop of 0.05 mL volume.

Average sized drop will reach TV at a height of about 7 feet.

Low Velocity - This type of spatter is usually caused by an impact to the blood source at a rate of 5 feet per second and is usually about 4 millimeters in diameter.

Medium Velocity - This type of spatter is usually caused by an impact to the blood source at a rate of 5-25 feet per second.  Stains caused by this type of force are usually 1-3 millimeters in diameter, but may be larger or smaller.

High Velocity - This type of spatter is usually caused by an impact to the blood source in excess of 100 feet per second and is usually less than 1 millimeter in diameter, although it can be larger or smaller.

Blood striking a hard surface will not spatter unless the surface is rough. (Page 306)

Blood cast at an angle will have an elongated appearance at the sight of impact and leave a trailing edge that can help determine the direction it came from.

Area of convergence is determined by drawing lines from the leading edges of the stain through the long axis.

Where the lines come together is the general area where the blood came from.

The angle of impact can be determined by measuring the blood stain and using the formula below.

Arcsin X

width (mm)

length (mm)

​

=

Degree of angle

Arcsin X

2.4 (mm)

3.1 (mm)

=

50.73 ^o angle

Sample Problem