Haematocrit (packed cell volume), the fraction of blood that is red cells.
What it is
Also called PCV or HCT; UK labs often report as a fraction (L/L) or sometimes as a percentage. It moves closely with haemoglobin.
Why it matters
Haematocrit moves with haemoglobin. Low values suggest anaemia or dilution; high values may reflect dehydration or true polycythaemia. Sex-specific adult ranges are usual.
Hydration on the day strongly affects this number, a post-sauna or post-race sample can mislead.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Haematocrit, with arterial oxygen saturation, determines arterial oxygen content. Very high haematocrit raises viscosity and cardiac workload; very low haematocrit limits oxygen delivery to muscle and brain.
For athletes
Dehydration after long sessions falsely raises haematocrit. Anti-doping and health contexts care about true red-cell mass versus plasma volume shifts. Re-test hydrated and never manipulate haematocrit with unsupervised agents.
