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Haematology
Haematocrit (Hct)
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Haematocrit is the fraction of blood volume occupied by red cells. On most analysers it is calculated from the red-cell count and MCV rather than measured by centrifugation.
Reference interval
| Conventional (%) | SI (L/L) | |
|---|---|---|
| Men | 41–53 % | 0.41–0.53 L/L |
| Women | 36–46 % | 0.36–0.46 L/L |
Specimen: Whole blood (EDTA) · Conventional × 0.01 = SI
Causes of high values
Polycythaemia, erythrocytosis from hypoxia, dehydration or diuretic use, and high altitude.
Causes of low values
Anaemia of any cause, acute haemorrhage after equilibration, overhydration and pregnancy (haemodilution).
Pre-analytical and method notes
Values depend on age, sex, altitude and method; reference intervals differ between laboratories. Marked leucocytosis, hyperglycaemia and abnormal MCV may bias calculated values; very high haematocrit raises blood viscosity.
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. Elsevier — Tier 3 (textbook)
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