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HCT (haematocrit) measures the amount of space (volume) within the blood that is taken up by red blood cells.

What might a low result mean?

Low levels of HCT (in combination with a low haemoglobin result) indicates that you may have anaemia. Anaemia has a wide variety of causes, including iron or vitamin B12 deficiency, chronic kidney disease, or bleeding from the digestive tract.

Anaemia can also arise when the body excessively destroys red blood cells, as found in conditions such as haemolytic anaemia.

What might a high result mean?

Elevated levels of HCT indicate that you may have polycythaemia, meaning you have an excessively high number of red blood cells. This conclusion is normally arrived at in conjunction with a high haemoglobin result. Polycythaemia can arise when oxygen levels in the body drop, and the body tries to compensate by producing more red blood cells. This can happen in people with congenital heart defects and lung diseases such as COPD.

Raised levels of HCT can also be found in some smokers.