As part of a full blood count (FBC), a general blood screening test which may be requested for a variety of symptoms such as headaches, blurred vision, tiredness, itchy skin, difficulty in breathing and dizziness.
A blood sample taken from a vein in your arm or by a finger-prick (children and adults) or heel-prick (newborns)
No test preparation is needed
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 increases 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, or the blood cells are diluted by increases in total volume (haemodilution, for example occurring during pregnancy).
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, or haemodilution. Haemodilution is usually obvious due to administration of a bolus of intravenous fluids (water containing solutions into the blood stream) or pregnancy. Further testing may be necessary to determine the exact cause of 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.
In primary polycythaemia (polycythaemia vera, PV, or, polycythaemia rubra vera, PRV) the bone marrow overproduces red blood cells of its own accord.
More commonly polycythaemia is 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
- Drug induced - testosterone, growth hormone, EPO and diuretics
- 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 pressure of oxygen available at these heights.
Recent blood transfusion may give a misleading result.
You may have an ultrasound scan of the kidneys if a high PCV result is detected and possibly a blood test called EPO and JAK2.
In polycythaemia vera you may also have increased white cell cells and platelets.
How do you treat anaemia?
How do you treat polycythaemia?
Treatment aims to prevent symptoms and complications and treat underlying causes. This may be done by removing blood or taking medication to reduce PCV. You may be given medication to prevent blood clots. Improving lifestyle such as stopping smoking, drinking less alcohol and losing weight can decrease risk of potential blood clots.
Can I measure my PCV at home?
Is anyone more at risk for abnormal PCV values?
On This Site
Tests: Full Blood Count, Haemoglobin, RBC Count, Blood Film, Iron Tests, Reticulocyte Count, Vitamin B12 and Folate, Bone Marrow Aspiration and Biopsy, G6PD, Erythropoietin, Haemoglobin Variants
Elsewhere On The Web
British Society for Haematology guidelines on diagnosis and management of polycythaemia vera
British Dietetic Society Food Fact Sheets: Folic acid
NHS advice for iron deficiency anaemia
National Kidney Federation; Anaemia
NHS; Quit Smoking