Polycythemia is an increased number of red blood cells in the blood. In polycythemia, the levels of hemoglobin (Hgb), hematocrit (Hct), or the red blood cell (RBC) count may be elevated when measured in the complete blood count (CBC), as compared to normal.
Hemoglobin levels greater than 16.5 g/dL (grams per deciliter) in women and greater than 18.5 g/dL in men suggest polycythemia. In terms of hematocrit, a value greater than 48 in women and 52 in men is indicative of polycythemia.
Production of red blood cells (erythropoiesis) occurs in the bone marrow and is regulated in a series of specific steps. One of the important enzymes regulating this process is called erythropoietin (Epo).
The majority of Epo is produced and released by the kidneys, and a smaller portion is released by the liver.
Polycythemia can result from internal problems with the production of red blood cells. This is termed primary polycythemia.
If polycythemia is caused due to another underlying medical problem, it is referred to as secondary polycythemia.
Most cases of polycythemia are secondary and are caused by another medical condition. Primary polycythemias are relatively rare.
One percent to five percent of newborns can have polycythemia (neonatal polycythemia).
Signs and symptoms
Mild cases of polycythaemia may not cause any problems, but some people with polycythaemia can experience:
- blurred vision
- red skin, particularly in the face, hands and feet
- high blood pressure
- discomfort in the tummy (abdomen)
- periods of confusion
- bleeding problems – such as nosebleeds and bruising
- gout – which can cause joint pain, stiffness and swelling
- itchy skin – especially after a bath or shower; this is the result of white blood cells (levels of which can also be high) releasing the chemical histamine
You should make an appointment to see your GP if you have persistent symptoms of polycythaemia.
When to seek immediate medical advice
The slow blood flow associated with polycythaemia can also cause blood clots. These can be serious because they can put you at risk of life-threatening problems such as heart attacks, pulmonary embolisms (a blockage in the blood vessel that carries blood from the heart to the lungs) and strokes.
In some cases, a blood clot – known as deep vein thrombosis (DVT) – may form in your leg, before moving elsewhere in your body.
Signs of DVT or a pulmonary embolism can include:
- pain, swelling, redness and tenderness in one of your legs
- a heavy ache in the affected area
- warm skin in the area of the clot
- chest or upper back pain
- coughing up blood
- feeling lightheaded or dizzy
If you experience any of the above symptoms, seek medical help immediately. You should also seek emergency medical help if you think you or someone you are with is having a heart attack or stroke.
Polycythemia Risk Factors
Some of the risk factors for polycythemia include:
- chronic hypoxia;
- long-term cigarette smoking;
- familial and genetic predisposition;
- living in high altitudes;
- long-term exposure to carbon monoxide (tunnel workers, car garage attendants, residents of highly polluted cities); and
- Ashkenazi Jewish ancestry (may have increased frequency of polycythemia vera due to genetic susceptibility).
Polycythemia Primary Causes
In primary polycythemia, inherent or acquired problems with red blood cell production lead to polycythemia.
Two main conditions that belong to this category are polycythemia vera (PV or polycythemia rubra vera [PRV]) and primary familial and congenital polycythemia (PFCP).
Polycythemia vera (PV) is related to a genetic mutation in the JAK2 gene, which is thought to increase the sensitivity of bone marrow cells to Epo, resulting in increased red blood cell production.
Levels of other types of blood cells (white blood cells and platelets) are also often increased in this condition.
Primary familial and congenital polycythemia (PFCP) is a condition related to a mutation in the EPOR gene and causes increased production of red blood cells in response to Epo.
How polycythaemia is diagnosed
Polycythaemia can be diagnosed by carrying out a blood test to check the number of red blood cells in your blood (red blood cell count) and the amount of space the red blood cells take up in the blood (haematocrit level).
A high concentration of red blood cells in your blood suggests you have polycythaemia.
Your GP may have ordered a blood test because you reported some of the above symptoms or complications, but polycythaemia is sometimes only discovered during a routine blood test for another reason.
Your GP may refer you to a haematologist (specialist in conditions affecting the blood) for further tests to confirm the diagnosis and to determine the underlying cause, such as a blood test to look for the faulty JAK2 gene and an ultrasound scan of your abdomen to look for problems in your kidneys.
Treatment for polycythaemia aims to prevent symptoms and complications (such as blood clots), and treat any underlying causes. Some of the main treatments used are described below.
Venesection is the simplest and quickest way of reducing the number of red cells in your blood.
It may be recommended if you have PV, a history of blood clots or symptoms suggesting your blood is too thick (see above).
Venesection involves removing about one pint (half a litre) of blood at a time, in a similar way to the procedure used for blood donation.
How often this is required will be different for each person. At first you may need the treatment every week, but once your condition is under control you may only need it every 6-12 weeks or less.
Medication to reduce the production of red blood cells
In cases of PV, medication may be prescribed to slow down the production of red blood cells.
Many different medications are available that can help do this, and your specialist will take into account your age and health, response to venesection and red blood cell count when choosing the most appropriate one for you.
- hydroxycarbamide – generally tolerated well, but should not be taken by pregnant women or women trying to conceive
- interferon – can be taken in pregnancy, but may cause unpleasant side effects, such as hair loss and flu-like symptoms
Medication to prevent blood clots
Daily low-dose aspirin tablets may be prescribed to help prevent blood clots and reduce the risk of serious complications, if you have PV.
You may also be offered treatment with low-dose aspirin if you have apparent or secondary polycythaemia and another condition affecting your blood vessels, such as coronary heart disease or cerebrovascular disease.
Treating and preventing other conditions
Some people may also need treatment for any other symptoms or complications of polycythaemia they have, or for any underlying cause of the condition.
For example, you may be given medication to help relieve itching, manage COPD or treat gout. Read more about treatments for itching, treating COPD and treating gout.
As well as improving some cases of apparent polycythaemia, making healthy lifestyle changes can also reduce your risk of potentially serious blood clots for people with all types of polycythaemia.
Having polycythaemia means you are already at high risk of a blood clot, and being overweight or smoking will only increase this risk further.
You may find the following advice and information helpful:
- losing weight
- healthy weight calculator
- preventing cardiovascular disease
- managing high blood pressure
- stopping smoking
The outlook for polycythaemia largely depends on the underlying cause.
Many cases are mild and may not lead to any further complications. However, some cases – particularly cases of PV – can be more serious and require long-term treatment.
If well controlled, polycythaemia should not affect your life expectancy, and you should be able to live a normal life.
However, people with PV can have a slightly lower life expectancy than normal due to the increased risk of problems, such as heart attacks and strokes.
PV can also sometimes cause scarring of the bone marrow (myelofibrosis), which can eventually lead to you having too few blood cells.
In some rare cases, the condition can develop into a type of cancer called acute myeloid leukaemia (AML).
If you have polycythaemia, it is important to take any medication you are prescribed and keep an eye out for signs of possible blood clots to help reduce your risk of serious complications.
Many causes of secondary polycythemia are not preventable. However, some potential preventive measures are:
- smoking cessation;
- avoid prolonged carbon monoxide exposure; and
- appropriate management of diseases such as chronic lung disease, heart disease or obstructive sleep apnea.
Primary polycythemia due to mutation of genes is generally not preventable.