Plasma
Definition
The liquid fraction of blood (approximately 55% by volume), containing water, proteins (albumin, immunoglobulins, fibrinogen, clotting factors), electrolytes, glucose, hormones, and dissolved gases. The principal source of species-specific proteins used in precipitin tests.
- Blood fraction
- Approximately 55% by volume
- Composition
- Water, proteins, electrolytes, glucose, hormones, gases
- Key proteins
- Albumin, immunoglobulins, fibrinogen, clotting factors
- Forensic use
- Source of species-specific proteins in precipitin testing
Common questions
How does plasma differ from serum in a forensic biology context?+
Plasma is the liquid fraction of unclotted blood and still contains fibrinogen and other clotting factors, while serum is what remains after blood has clotted and those clotting proteins have been consumed, which matters when choosing a sample for certain protein-based tests.
Why is plasma protein content relevant to species identification of a bloodstain?+
The species-specific proteins carried in plasma are what a precipitin test detects when it reacts a bloodstain extract against an antiserum raised to a particular species, allowing analysts to determine whether a stain is human or from another animal.
Related terms
- Haematocrit
- The proportion of blood volume occupied by red blood cells, approximately 45% in adult males and 40% in adult females. Influences the...
- Haemoglobin
- The iron-containing oxygen-transport protein in red blood cells, composed of four polypeptide subunits each with a haem prosthetic group. Its pseudoperoxidase activity...
- Haemolysis
- The rupture of red blood cells and release of haemoglobin into the surrounding fluid. In casework, haemolysis of aged stains, wet stains,...
- Methaemoglobin
- An oxidised form of haemoglobin in which ferrous iron (Fe2+) is converted to ferric iron (Fe3+), unable to carry oxygen. Its formation...
- Serum
- The fluid that remains after blood has clotted and the clot has been removed. It is plasma minus fibrinogen and other clotting...