About Hematocrit
Hematocrit is the percentage of blood volume occupied by red blood cells, and it rises and falls in parallel with haemoglobin — making it a near-redundant but confirmatory measure of anaemia and polycythaemia. Low hematocrit confirms anaemia (insufficient red cells or haemoglobin); high hematocrit is seen in dehydration, chronic mountain sickness, or polycythaemia vera, and increases blood viscosity and clotting risk. Athletes in endurance sports monitor hematocrit closely because training at altitude (or illicit EPO use) raises it significantly.