The Packed Cell Volume test is also called the haematocrit test. It is used to diagnose anaemia, polycythaemia or dehydration in patients. Generally, the test is a part of a full blood count and is commonly carried out to monitor response to treatment, estimate need for blood transfusions, etc. Blood is a mixture of plasma and cells. The packed cell volume (PCV) test measures how much of the blood consists of cells. A PCV of 50% means 50 ml of cells are present in 100 ml of blood. If the number of red blood cells increases, the PCV also rises. It also increases as a result of dehydration.