Blood Test
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What is blood made of?
55% Plasma 1% white blood cells and platelets 44% red blood cells
Red blood cells - science
erythrocytes disk shaped no nucleus at maturity because it got rid of it to carry more oxygen. carries oxygen everywhere in the body Technically not a cell because no nucleus.
Red blood cells - forensics
Contain hemoglobin which changes colour over time due to lack of oxygen, allowing scientists to determine approximately when the blood left the body.
White blood cells - science
leukocytes large contain a nucleus defend against foreign invaders and provide immunity to virus.
White blood cells - forensics
have a nucleus, which contains DNA
Platelets - science
thrombocytes help with blood clotting so you don’t bleed out. All different shapes and sizes in order to fit to clot. repair damaged blood vessels.
Platelets - forensics
Helps impact the thickness and viscosity of blood, influencing how spatter falls.
Plasma - science
the watery, liquid part of blood that transports antibodies, hormones, nutrients, vitamins, minerals, sugar, and helps move waste away.
Plasma - forensics
Thickness causes blood to behave in certain ways.
What three questions must be answered when there is suspected blood at a scene?
IS it blood? is it HUMAN blood? WHOSE blood is it?
IS it blood?
Kastle-Meyer indicator test - causes colour change Luminol test - uses luminol and UV light
Kinds of blood evidence
Samples Droplets Spatter
Cohesion
blood likes to stick to itself, so it resists flattening out as long as the surface is smooth.
Adhesion
Blood likes to stick to other things.
Satellite
when a tiny baby drop is fully separated from the parent drop
Parent drop
the main drop
spines
little spikes that come off the parent drop but are still attached.
Effect of height on blood drops
The blood drop with become larger in diameter and may have more satellites and spines due to a higher velocity from a farther fall.
Effect of surface on blood
On a smooth surface, cohesion will be intact, but the more porous or rough the surface, the more spines and satellites will occur. The drop may even be slightly smaller.
Categories of blood spatter
passive, projected, and transfer
Passive blood spatter
blood falling directly to the surface at a 90 degree due to the force of gravity.
Projected blood spatter
patterns that occur when force is applied to the source of blood. Types: Impact, cast off, arterial spurt, and expired.
Transfer blood spatter
When wet blood contacts a dry surface. Types: Wipe and Swipe
Low impact
basically a passive drop. more the 4 mm average velocity or 5 ft/sec looks like rundish drops bloody nose, one strike with a blunt object, etc