Haematocrit

Women: 0.36 to 0.46 L/L · Men: 0.4 to 0.5 L/L

Ranges differ by sex and in pregnancy, and some laboratories print the value as a percentage; use the range your lab printed.

The haematocrit is the fraction of the blood that is made up of red blood cells. If a tube of blood were left to settle, it is the proportion of the column occupied by the packed red cells, which is why it is also called the packed cell volume. It moves closely with the haemoglobin.

It is part of the full blood count and is looked at alongside haemoglobin. Doctors also use it when they are looking into conditions where the blood has too many red cells, or is too concentrated.

• Dehydration on the day of the test
• Smoking
• Living or training at altitude
• Some lung and heart conditions
• Testosterone and some other hormone medicines
• Conditions where the bone marrow makes too many red cells

• Blood loss, including heavy periods
• Low iron, vitamin B12 or folate
• Pregnancy, because the blood volume expands
• Long-term kidney disease
• Long-term inflammatory illnesses
• Some medicines, including chemotherapy

• Drinking a lot of fluid before the test can lower it slightly
• Being dehydrated can raise it slightly
• Analysers calculate it slightly differently, so small differences between laboratories are common

No fasting needed. It tracks haemoglobin closely, so the trend over time is more useful than a single value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.