Serology Notes

Introduction to Forensic Science and Serology

  • Forensic Science: The use of scientific methods and principles to investigate crime.

  • Serology:

    • Analysis of body fluids (saliva, semen, urine, blood).

    • Important in forensic labs from 1950 to late 1980s.

    • DNA techniques now dominate due to accuracy, yet serological tests remain in use.

Blood Characteristics

  • Components of Blood:

    • Plasma: 55% of blood, fluid portion.

    • Cells: 45% of blood, includes:

      • Erythrocytes (red blood cells)

      • Leukocytes (white blood cells)

      • Thrombocytes (platelets)

    • Serum: liquid that separates after blood coagulation.

  • Blood Volume:

    • Accounts for ~8% of body weight.

    • Average: 5-6 liters (males), 4-5 liters (females).

    • 40% volume loss leads to shock; 1.5 liters internal loss causes incapacitation.

General and Genetic Blood Terminology

  • General Terminology:

    • ABO Blood Groups: Defined by presence/absence of A or B antigens.

    • Rh Factor: Determines if blood is positive or negative.

    • Antigen/Antibody: Substances involved in immune reactions.

    • Agglutination: Clumping of red blood cells.

  • Genetic Terminology:

    • Genotype: Genetic makeup represented by letters (e.g., IAIA).

    • Phenotype: Observable traits.

    • Heterozygous: Different alleles for a trait.

    • Homozygous: Same alleles for a trait.

Blood Detection and Analysis

  • Unknown Stain Investigation:

    • Is it blood? Is it human blood? Whose blood is it?

    • Tests for blood type, toxins, and deposition methods.

  • Presumptive Tests:

    • Kastle-Meyer color test: pink color indicates blood.

    • Leucomalachite and Luminol tests: other color changes identify blood.

    • Microcrystalline tests: form crystals specific to blood.

Differentiating Human vs. Animal Blood

  • Microscopic Survey & Precipitin Test: Detects human proteins using antibodies.

  • Characteristic Differences: Notable differences between human and various animal blood forms.

Human Blood Characteristics

  • Red Blood Cells: No nucleus, abundant (5-6 million per mm³).

  • White Blood Cells: Fewer (5-10,000 per mm³), vital to immune defense.

  • Platelets: Tiny fragments crucial for clotting (350,000-500,000 per mm³).

Historical Perspective of Blood Typing

  • Karl Landsteiner's discovery of blood types and Rh factor in early 1900s.

  • Percentage of Rh positivity across different ethnic groups.

  • Subjective nature of blood typing methods and distinction of blood types.

Blood Pattern Reconstruction

  • Analyzing blood stains can reveal:

    • Source and direction of bloodshed.

    • Victim and assailant positions.

    • Number of attacks.

  • Techniques include:

    • Genetic marker typing

    • Age and sex determination

    • Blood stain characteristics

Blood Spatter Interpretation

  • Bloodstain Terminology:

    • Angle of Impact: strike angle alters stain shape.

    • Transfer Patterns: unique patterns derived from blood transfer.

    • Velocity Types: Low, Medium, High - affects stain size and appearance.

    • Point of Origin: 2D & 3D locations determine blood source.

Environmental Influence on Blood Stains

  • Impact of Surface Texture: Affects stain shape (smooth vs rough).

  • Distance and Direction: Estimating height and origin of blood based on splash patterns.

Conclusion of Blood Evidence and Detection

  • Blood type can be class evidence, DNA can become individual evidence.

  • Analysis of blood patterns can provide circumstantial evidence in investigations.

  • Secretors: Individuals with detectable blood antigens in various body fluids.

  • Sperm identification via tests for specific enzymes and proteins in seminal fluid.