Hematocrit (HCT)
Also called: Hematocrit, Haematocrit, HCT, PCV, Packed cell volume, Ht
The percentage of your blood that is red cells. It moves together with haemoglobin and tells the same story — low in anaemia, high in dehydration or when the body over-produces red cells — but is also swayed by how hydrated you are.
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What does Hematocrit (HCT) measure?
Hematocrit is the proportion of blood volume occupied by red blood cells, given as a percentage. It is a core part of the full blood count and tracks closely with haemoglobin (roughly three times the haemoglobin value in g/dL). Because it is a concentration, it is affected not only by red-cell mass but by plasma volume: dehydration concentrates the blood and raises the hematocrit, while over-hydration or pregnancy dilutes it and lowers it. A low hematocrit points to anaemia; a high one to dehydration or to genuine over-production of red cells (polycythaemia), whether primary (polycythaemia vera) or secondary to low oxygen, smoking or, rarely, an EPO-secreting process. It is always read alongside haemoglobin, red-cell count and the red-cell indices (MCV, RDW) to work out the cause.
What does a high Hematocrit (HCT) level mean?
- Dehydration — the commonest cause; concentrated blood, corrects with fluids.
- Polycythaemia vera — a bone-marrow disorder over-producing red cells; often with high haemoglobin, itching and thrombosis risk.
- Secondary polycythaemia — chronic low oxygen (lung disease, sleep apnoea, high altitude), heavy smoking, or an EPO-secreting tumour.
- Testosterone therapy or anabolic steroids.
What does a low Hematocrit (HCT) level mean?
- Anaemia — of any cause (iron, B12/folate, chronic disease, blood loss); the hematocrit falls with the haemoglobin.
- Over-hydration / fluid overload — dilutional.
- Pregnancy — a normal dilutional fall.
- Recent bleeding.
When to discuss with a doctor
Hematocrit is interpreted with haemoglobin, not instead of it — the two move together, and the cause matters more than the number. A low hematocrit prompts the anaemia work-up (iron studies, B12/folate, blood-loss assessment). A high hematocrit should first be rechecked when well-hydrated; if it stays high, it needs evaluation for polycythaemia, including oxygen levels and, when primary polycythaemia is suspected, testing for the JAK2 mutation. A very high hematocrit thickens the blood and raises clot risk. Mediora.AI shows hematocrit next to haemoglobin and the red-cell indices so the pattern is read as a whole; the cause and any treatment belong with your doctor.