Bloodstains and bodily fluids

Properties of blood

1. Plasma: the liquid part of blood

2. Platelet form clots

3. Serum: part of plasma that carries protein and electrolytes

4. Fibrogen: Material that forms clots

5. Red blood cells: Cells that transport oxygen

6. White blood cells: Cells that fight infections

Physical Properties

1. Surface tension: the force that pulls surface molecules of liquid together

2. Viscosity: blood is 6x more viscous (flows 6x slower) than water 

3. Specific gravity: the weight of a substance relative to the weight of an equal volume of water

   1. Specific gravity is slightly higher than water

Misting

Forward exit wound splatter is much larger 

Back Entrance wound spatter is less blood

• The misting pattern is associated with high-velocity impacts such as gunshots, explosions, and high-speed vehicle collisions.

Blood patterns 

Low velocity bloodstain (beating or blunt weapon) 4-6 mm in diameter

Medium velocity bloodstain (stabbings): 1-3 mm in diameter

High velocity bloodstain (gunshots): 0.1 mm in diameter

Angle of impact = 90°: circular shape

Angle of impact <90°: elliptical shape

Satellites and spikes: determine which direction the blood drop moves before hitting a surface

Area of origin: narrow end of an elliptical bloodstain usually shows its directionality

• Draw a straight line through each bloodstain to find the area of convergence, or the location of the blood source in a 2D perspective

Altered Bloodstains

Clots: 

• happens after blood leaves the body 

• blood forms a jellylike mass and retracts from the serum

Skeletonized stain

• happen when the center of a dried bloodstain flakes away, leaving the rim 

Void areas

• Void areas happen when something is blocking the blood source

Identifying blood 

1. Chemiluminescence: include luminol and fluorescein

2. Kastle-Meyer test: chemical test that reacts with hemoglobin and turns pink if positive

Other body fluids

1. Seminal fluid

   1. Second most common type of fluid found in forensic cases

   2. Volumes range from 2-6 mL and contain 100-150 million spermatozoa (sperm cells)

   3. Azoospermia (no sperm in the ejaculate)  is lacking spermatozoa

   4. Can test for seminal acid phosphatase (SAP) instead 

      1. enzyme found in high concentrations in seminal fluid, making it a useful indicator for the presence of semen

   5. Can find DNA in seminal fluid, which can identify perpetrator

2. Saliva

   1. Secretion that contains water, mucus, proteins, salts, and enzymes

   2. Helps digest food

   3. Detecting saliva requires the starch-iodine test

   4. In the presence of iodine, starch changes color and appears blue

3. Urine

   1. Tests are performed less and less frequently because of the insensitivity of the tests and low success rate with DNA profiling.

   2. Urine detection relies on finding two organic compounds

      1. Urea

      2. Creatinine