Haematocrit
Definition
The proportion of blood volume occupied by red blood cells, approximately 45% in adult males and 40% in adult females. Influences the volume of haemoglobin and nuclear DNA available from a given sample.
- Definition
- Proportion of blood volume occupied by red blood cells
- Adult male
- Approximately 45%
- Adult female
- Approximately 40%
- Forensic relevance
- Affects available haemoglobin and nuclear DNA yield
Common questions
Why does haematocrit matter for DNA recovery, given that red blood cells lack a nucleus?+
Mature red blood cells have no nucleus and contribute no nuclear DNA, so the nuclear DNA in a blood sample comes almost entirely from white blood cells. Haematocrit is relevant less directly, since it affects overall sample composition and the concentration of haemoglobin used in presumptive and confirmatory blood tests.
Does a low or high haematocrit change how a bloodstain looks or tests at a scene?+
It can influence stain colour and drying behaviour somewhat, since haematocrit affects the proportion of red cells to plasma, but presumptive and confirmatory blood tests target haemoglobin and other blood-specific proteins rather than haematocrit directly, so normal physiological variation does not typically affect test outcomes.
Related terms
- 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...
- Plasma
- The liquid fraction of blood (approximately 55% by volume), containing water, proteins (albumin, immunoglobulins, fibrinogen, clotting factors), electrolytes, glucose, hormones, and dissolved...
- Serum
- The fluid that remains after blood has clotted and the clot has been removed. It is plasma minus fibrinogen and other clotting...