PCV
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
A PCV (packed cell volume) test measures the proportion of blood made up of red blood cells using a blood sample taken from a vein in the arm. It is used to help assess conditions affecting red blood cells, such as anaemia, dehydration or polycythaemia.
Why get tested?
If your doctor suspects that you have anaemia (too few red blood cells), polycythaemia (too many red blood cells), or dehydration
When to get tested?
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.
Sample required?
A blood sample taken from a vein in your arm or by a finger-prick (children and adults) or heel-prick (newborns)
Test preparation needed?
No test preparation is needed
Common questions
This test is used to diagnose or evaluate anaemia (decrease of red blood cells), polycythaemia (increase in red blood cells) or dehydration; which may be referred to as relative polycythaemia.
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:
- Monitoring treatment of anaemia, polycythaemia or dehydration.
- Monitoring the need for or effectiveness of blood transfusions, monitoring of ongoing bleeding to check its severity.
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
- Bleeding
- 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
- Smoking
- Liver or kidney disease
- Obesity
- 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
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.
Treatment will depend upon the type of anaemia and the cause. Folic acid, vitamin B12 replacement, iron, and packed red cell transfusion are some therapies used to treat anaemia.
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.
No. This test is performed by trained laboratory personnel.
People who have a chronic illness (such as rheumatoid arthritis), an inherited blood disorder, or malnutrition are at risk for an abnormal PCV. Women of childbearing age may have temporary decreases in PCV during menstrual periods and pregnancy.