A blood sample taken from a vein in your arm or by a finger-prick (children and adults) or heel-prick (newborns)
Blood is a mixture of cells and plasma. The packed cell volume (PCV) is a measurement of the proportion of blood that is made up of cells. The value is expressed as a percentage or fraction of cells in blood. For example, a PCV of 40% means that there are 40 millilitres of cells in 100 millilitres of blood.
Red blood cells account for nearly all the cells in the blood. The PCV rises when the number of red blood cells increases or when the total blood volume is reduced, as in dehydration. The PCV falls to less than normal, indicating anaemia, when your body decreases its production of red blood cells or increases its destruction of red blood cells.
How is the sample collected for testing?
A sample is obtained by taking blood through a needle placed in a vein in the arm or by a finger-prick (for children and adults) or a heel-prick (for newborns).
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
When is it requested?
The PCV is normally requested as a part of the full blood count (FBC). It is also repeated at regular intervals for many conditions, including:
What does the test result mean?
A decreased PCV indicates anaemia. Further testing may be necessary to determine the exact cause of the anaemia.
Conditions that can result in a low PCV include
- Nutritional - iron, vitamin (e.g. B12 or folate) or other mineral deficiencies
- Inflammatory conditions such as rheumatoid arthritis
- Kidney disease (healthy kidneys secrete a hormone erythropoietin or “epo” which stimulates red blood cell production in the bone marrow)
- Cirrhosis of the liver
- Haemolysis, where the red cells are being destroyed prematurely either due to attack by the body’s immune system, due to organ damage or due to inherited abnormalities of the red cells or the haemoglobin they contain
- Bone marrow disorders such as aplastic anaemia, myelodysplastic syndrome, leukaemia, lymphoma or myeloma
- Some medicines– including chemotherapy
The most common cause of increased PCV is dehydration, and with adequate fluid intake, the PCV returns to normal. However, it may reflect a condition called polycythaemia where there are too many red cells.
Primary polycythaemia (polycythaemia rubra vera or PRV)—is means the bone marrow is overproducing red blood cells of its own accord.
More commonly polycythaemia is a due to factors outside the bone marrow (secondary polycythaemia). Causes of secondary polycythaemia include:
- Some lung or heart diseases where the bone marrow manufacturers more red blood cells in order to carry enough oxygen throughout your body
- Excessive alcohol consumption
- Liver or kidney disease
- Some tumours which can secrete erythropoietin (“epo”), stimulating the production of red blood cells
- Rare inherited haemoglobins, which don’t release enough oxygen to the body
Is there anything else I should know?
Pregnancy usually causes a slightly decreased PCV due to extra fluid in the blood.
Living at high altitudes causes an increased PCV - this is your body's response to the decreased oxygen available at these heights.
How do you treat anaemia?
Can I measure my PCV at home?
Is anyone more at risk for abnormal PCV values?