Serology and Bloodstain Pattern Analysis - Forensics

Main functions of blood

Transport, regulation, and protection

Transport

Oxygen, nutrients, metabolic wastes, hormones

Regulation

Temperature, pH, fluid volume

Protection

Prevents blood loss and infection

Hematopoiesis

Production of blood in bone marrow

Formed elements

Living blood cells (45%)

Plasma

Nonliving fluid 55% of its volume, primarily water (92%) with proteins, nutrients, and clotting factors, acting as a transport medium for cells and vital substances, helping regulate pressure, temperature, and fight infections, and is crucial for transfusions and treatments for rare diseases

Red Blood Cells

AKA erythrocytes

Normal RBC count

4-6 million cells in every drop of blood

Main function of RBCs

Transport oxygen and carbon dioxide

Hemoglobin

Contains iron used to transport oxygen

White Blood Cells

WBCs, AKA leukocytes

Agranulocytes

Type of white blood cells

Lymphocyte (WBC)

Increases immune response via antibodies or direct cell attack

Platelets

AKA thrombocytes

Normal platelet count

150K - 400K cells in every drop of blood

Main function of platelets

Seal small tears in blood vessels; blood clotting

ABO Blood Typing

Determined by proteins on the surface of erythrocytes (RBCs)

Type A blood

A antigens only

Type B blood

B antigens only

Type AB blood

A & B antigens

Type O blood (+ or -)

Neither A nor B antigens (However if it is positive it has RH factor)

Rh factor

Presence/absence of Rh is represented by +/-

Type A+ blood

A and Rh antigens

Type O- blood

AB nor Rh antigens

Antibodies in Type A blood

Anti-B antibodies

Antibodies in Type B blood

Anti-A antibodies

Antibodies in Type AB blood

No antibodies

Antibodies in Type O blood

Anti-A and Anti-B antibodies

Serology

Laboratory tests that confirm/exclude presence of a blood type

Angle of Impact

Angle formed between a path of a blood drop and the surface it contacts

Forward spatter

Blood that travels away from source of force

Back spatter

Blood directed back at the source of force

Low-velocity spatter

Produces blood drops with diameter greater than 3mm

Medium-velocity spatter

Produces blood drops with diameter of 1 to 3mm

High-velocity spatter

Produces blood drops with diameter of 1mm or less

What is the composition of blood plasma?

Plasma is a yellowish liquid that carries nutrients, hormones, proteins, and waste, and helps regulate temperature and pH.

What is the primary function of red blood cells (RBCs)?

RBCs contain hemoglobin and transport oxygen to tissues and carbon dioxide away.

What role do white blood cells (WBCs) play in the body?

defend against infections and foreign invaders.

What are platelets and their function?

Platelets are cell fragments that help with clotting and wound repair.

How is blood type determined?

By antigens on the surface of red blood cells.

What antigens are present in Type A blood?

A antigens.

What antibodies are present in Type B blood?

Type B blood has Anti-A antibodies.

What is the universal donor blood type?

Type O negative because it has no antigens.

What is the universal recipient blood type?

Type AB positive because it has all antigens.

What are the three key questions in forensic blood analysis?

1. Is it blood? 2. Is it human blood? 3. Whose blood is it?

What are presumptive tests in blood analysis?

(like Kastle-Meyer and luminol) detect the presence of blood by color or chemiluminescence.

What is the purpose of DNA profiling in forensic analysis?

DNA profiling identifies the individual from the blood sample.

What is the significance of bloodstain pattern analysis?

It provides information about the position of the victim/assailant, type of weapon, number of blows, and sequence of events.

What is a parent drop in bloodstain analysis?

The parent drop is the original stain from which satellite stains originate.

How does the height of a blood drop affect its stain?

Higher drops create larger stains with more satellite droplets.

What is the formula for calculating the angle of impact of a blood drop?

Angle of impact = arcsin(width/length).

What is the point of convergence in bloodstain analysis?

Where lines drawn through stains show the 2D origin of blood spatter.

What type of evidence do bloodstains represent?

Biological evidence.

What precautions should be taken when handling blood in a forensic setting?

Wear gloves, masks, and goggles, and treat all blood as potentially infectious.

What is the definition of a hypothesis in science?

A hypothesis is a testable statement predicting an outcome based on the relationship between variables.

What characterizes a strong hypothesis?

is clear, specific, measurable, and addresses a cause-effect relationship.

What happens if a hypothesis is confirmed?

If confirmed, it supports the theory and can be refined further.

What should be done if a hypothesis is denied?

If denied, the hypothesis should be revised, and new explanations should be investigated.