Haematocrit (PCV)

Red cell volume, anaemia

Haematocrit, also called packed cell volume (PCV), is the share of your blood volume made up of red blood cells. It rises when the blood becomes more concentrated, for example with dehydration or plasma leakage in dengue, and falls when there are too few red cells, as in anaemia. It is part of a complete blood count but can also be requested on its own.

• To watch for plasma leakage during dengue fever, where a rising PCV is a warning sign
• To check for anaemia or blood loss
• To assess dehydration
• To look for too many red cells, for example with heavy smoking, long-term lung disease or a bone marrow condition
• To follow recovery after bleeding or a blood transfusion

You can eat and drink normally, and staying well hydrated matters, because dehydration can make the result appear high. Carry on with your usual medicines unless your doctor gives other advice.

Sample

Blood sample

How it works

A trained collector comes to you and takes a small blood sample from a vein in your arm, which only takes a few minutes. During dengue, repeat samples can be collected at home as often as your doctor advises.

Report

Within 24 hours of collection.

Your haematocrit is reported with the laboratory's range, which differs for men, women and children. A low value suggests anaemia or blood loss, while a high value can mean dehydration or an excess of red cells. During dengue, a rising haematocrit together with a falling platelet count can signal plasma leakage and needs prompt medical attention. Your doctor will interpret the result with your symptoms and other blood counts.

One test: Haematocrit (PCV), from one blood sample.