Tests for polycythaemia vera (PV)
You will need tests to decide if you have PV. If your doctor confirms that PV is the right diagnosis you will also have tests to monitor the PV and manage your risk of developing blood clots.
Tests to diagnose PV
There is a range of health conditions that can cause high levels of red blood cells, such as other types of cancer, lung disease, sleep apnoea (difficulty breathing at night), smoking and excessive drinking. So your hospital team will need to run tests to make sure that PV is the correct diagnosis.
A full blood count or FBC is a simple blood test which aims to measure how many of each type of cell there is in your blood. A sample of your blood is analysed by an automated counter.
This will show whether your blood cell counts – red cells, white cells and platelets – are within the normal range.
Your haematocrit is the proportion of red blood cells in your blood plasma (the liquid part of your blood). It’s basically a measure of how thick your blood is.
You will hear the word haematocrit a lot if you are diagnosed with PV. It’s one of the key things that will be monitored regularly.
You may have other blood tests to check on your general health and confirm that PV is the correct diagnosis. You doctor will look at:
- how well your kidneys and liver are working
- the level of iron in your blood
- the level of a hormone called erythropoietin (this controls the production of red blood cells).
Your doctor may also check the level of oxygen in your blood using pulse oximetry. This is a simple, painless test where a small device is placed on a finger or an ear lobe.
If your doctor doesn’t think you have PV, you may go on to have other tests.
These tests are done using a sample of your blood, which is analysed in a laboratory. Doctors are looking for a genetic change (mutation) in a gene known as JAK2.
Most people with PV have a JAK2 mutation. If you have a raised haematocrit and a JAK2 mutation, you will almost certainly be diagnosed with PV.
Tests if you don’t have a JAK2 mutation
If genetic tests don’t show a JAK2 mutation, then you will need more tests to confirm whether you have PV. This may include further blood tests, scans and a bone marrow biopsy.
You may have an ultrasound scan of your stomach area (abdomen). This is to examine an organ called the spleen which may be swollen if you have PV.
Most blood cells are made in the bone marrow – the spongy material inside some of your bones. But some blood cells are made in the spleen. If your bone marrow is not working properly, your spleen may need to work overtime, which makes it larger than normal, and sometimes painful.
The person who does the ultrasound scan is called a sonographer. They will apply gel to the surface of your abdomen and run a probe over the area they need to scan. The probe records images which can be seen on a computer screen.
To get a good image, the sonographer may need to press the probe firmly on to your abdomen. This will feel cold and may feel a bit uncomfortable, especially if your spleen is swollen.
A nuclear medicine scan is an accurate way of measuring the number of red cells in your blood. A radioactive substance – a tracer – is injected into a vein so that your red blood cells show up on images taken with a special camera.
The amount of radiation in the tracer is very low – no more radiation than you would normally be exposed to in the environment over the course of year.
Not all UK hospitals offer a nuclear medicine scan, but a blood test can also be used to get this information.
Some people have other scans such as a CT or MRI scan at the time of diagnosis. If you need these scans, your doctor will explain why. We have more information about scans used to diagnose and monitor blood cancer.
You may need a bone marrow biopsy to diagnose PV. This is a minor surgical procedure used to collect samples of bone marrow to test in the laboratory.
The samples are taken from the back of your pelvis (the ring of bones at the base of your spine). One sample is taken using a thin needle (an aspirate) and another using a thicker one (a trephine) to get a larger “core” of bone marrow.
These samples are examined under a microscope. Doctors will be looking for abnormal cells that are typical of PV.
You may find it helpful to read our information about bone marrow biopsies and talk things through with your hospital team or our Support Service.
Assessing your risk of blood clots or bleeding
In general, people with PV have a higher risk of thrombosis (blood clots) and haemorrhage (bleeding). Doctors will assess your risk based on:
- your age
- whether you have had problems with blood clots or bleeding before
- other medical conditions you may have
- your blood counts – the number of red cells, white cells and platelets in your blood.
If you have any other conditions that can also increase your risk of blood clots or bleeding (such as high blood pressure or high cholesterol), these will need to be managed effectively. This might involve a review of your medication and following general advice on healthy living.
The role of your GP
Your hospital team will recommend treatment to lower your risk of blood clots. But your GP plays an important part in your care too. They should give you regular check-ups, paying particular attention to other health conditions that might raise your risk of blood clots.
There are also things you can do to look after yourself when you have PV.
Tests to monitor PV
After you have been diagnosed with PV, you will have tests to monitor the condition and any treatment you’re having. The test you will have done routinely is a full blood count, or FBC.
Test results can be hard to understand, especially when you’re newly diagnosed. It’s fine to ask your hospital team to go through your FBC and explain what the figures mean. They will be checking if your treatment is keeping your blood cell counts within the normal range. They will look at:
- Haemoglobin level (Hb) – haemoglobin is the substance in red blood cells that carries oxygen around the body.
- Haematocrit (Hct) – the proportion of red blood cells in your blood (basically, a measure of how thick your blood is).
- White cell count (WCC or WBC) – the overall number of white blood cells in your blood.
- Platelets (Plt) – the number of platelets (clotting cells) in our blood.
- Neutrophils (Neut) – the number of neutrophils (a type of white blood cell) in your blood.
The words in brackets are the abbreviations hospitals often use when they record test results.
We have information about normal blood cell ranges but do check with your hospital team what the target range is for you. What’s normal can vary according to your sex and ethnic background.
Waiting for your test results
It’s important to have regular tests but waiting for test results can be an anxious time. If you would like support for this or any other feelings, our Support Service can help.
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