You have a number of different blood tests to help diagnose chronic myeloid leukaemia (CML).
Blood tests can:
- check your general health, including how well your liver and kidneys are working
- check numbers of blood cells
- help diagnose cancer and other conditions
The first test you have is a blood test and this is usually a full blood count. Many people don't have symptoms when they find out they have CML. They might be having a blood test for another reason.
Your blood sample is sent to the laboratory. A specialist doctor called a pathologist looks at your sample under a microscope. They can see the different types of cells and can count the different blood cells. They can also test for different kinds of chemicals and proteins in the blood.
Preparing for your blood tests
You can eat and drink normally before most blood tests. For fasting blood tests you need to stop eating and drinking beforehand. Your doctor will tell you for how long.
You sit or lie down to have the test.
A doctor, nurse or phlebotomist (person specialised in taking blood) chooses the best vein to use. This is usually from your arm or hand. Let them know if you are afraid of needles, get unwell with the sight of blood or are allergic to plasters or latex.
They put a tight band (tourniquet) around your arm above the area where they take the sample. You may need to clench your fist to make it easier to find a vein.
They clean your skin and then put a small needle into your vein. Next, they attach a small bottle or syringe to the needle to draw out some blood. They might fill several small bottles.
Once they have all the samples, they release the band around your arm. They then take the needle out and put pressure on the area with a cotton wool ball or small piece of gauze for a few minutes. This helps to stop bleeding and bruising.
Look away when they’re taking the blood if you prefer. Tell your doctor, nurse or phlebotomist if you feel unwell.
Getting your results
Ask the phlebotomist, doctor or nurse when and how you will get your results. Some results might be available quickly, such as a full blood count. But some other tests might take several weeks.
Blood sampling (phlebotomy) is a safe test. There is a possibility of:
- bleeding and bruising - pressing hard when the needle is removed can help to stop it
- pain - this is normally mild and can last for a few minutes
- swelling (oedema) - ask your nurse, doctor or phlebotomist to avoid an arm that is swollen or has a risk of swelling
- feeling faint or fainting - tell the person doing your blood test if you're feeling lightheaded or dizzy at any time
- infection - this is very rare
What is a full blood count?
A full blood count (FBC) measures the number of red cells, white cells and platelets in your blood.
- Red cells carry oxygen around our bodies. Haemoglobin is the part of the cell that carries oxygen. If you have a low red cell count, your doctor might say you’re anaemic (pronounced a-nee-mic). This can make you feel tired, short of breath and dizzy.
- White cells fight infections. There are several different types of white cells, including neutrophils and lymphocytes.
- Platelets help clot the blood. Symptoms of a low platelet count include abnormal bleeding, such as bleeding gums and nosebleeds.
There isn’t an exact range of normal for blood counts. The range of figures quoted as normal varies slightly between laboratories and also differs between men and women.
Some further laboratory tests may be carried out on your blood cells. These tests are also called chromosome analysis. Your haematologist may order these tests to look for changes (abnormalities) in your chromosomes. The tests are called cytogenetic tests or molecular analysis.
About 95 out of every 100 people with CML (95%) have an abnormality called the Philadelphia chromosome. This is when a gene called the ABL1 gene on chromosome 9 breaks off and sticks to a gene called the BCR gene on chromosome 22. It produces a new gene called BCR-ABL1. Testing for this genetic change can diagnose CML. Doctors also use it to see how well treatment for CML is working.
The BCR-ABL1 gene causes the cell to make too much of a protein called tyrosine kinase. This protein encourages leukaemia cells to grow and multiply. The main treatment for CML works by blocking this protein.
Watch this 2 minute video to explain what Philadelphia positive leukaemia is.
The human body is made up of trillions of cells. Inside each cell is a nucleus and within the nucleus are the cell’s chromosomes. There are 23 pairs in total.
Chromosomes are made up of DNA, which gives the instructions that tell a cell what to do. Sections of DNA are called genes. They carry the information that makes you you. For example, they tell your body what colour your hair will be or what colour your eyes will be.
Genes also tell your cells when to divide and grow, and when to die.
When cells divide to make new cells, they make exact copies of the chromosomes.
In Philadelphia chromosome positive leukaemia an abnormal change happens to chromosomes 9 and 22. Part of chromosome 9 breaks off where the gene ABL1 is located and part of chromosome 22 breaks off where the BCR gene is located. The broken parts swap places creating a new gene on chromosome 22.
This new chromosome is called the Philadelphia chromosome and the new gene is called BCR-ABL1. This new gene tells the cell to make a large quantity of a protein called tyrosine kinase which encourages leukaemia cells to grow.
There are targeted cancer drugs that can block the protein and stop the leukaemia from growing. These drugs are called tyrosine kinase blockers. You take them as tablets.
For more information about your type of leukaemia and treatments go to CRUK.org/about-cancer/leukaemia.
Other blood tests
Urea and electrolytes
These blood tests show how well your kidneys are working. Waste chemicals called urea and creatinine are produced by the body. Our kidneys remove them from our blood and get rid of them in our urine.
Electrolytes are substances such as sodium, potassium, chloride and bicarbonate.
Liver function tests (LFTs)
Liver function tests (LFTs) check how well your liver is working. LFTs look for levels of enzymes and proteins made by the liver or which are cleared by the liver. They include:
- alanine aminotransferase (ALT)
- aspartate aminotransferase (AST)
- alkaline phosphatase (ALP)
- gamma-glutamyl transferase (Gamma GT)
They might be raised if you have a blockage in your liver or bile duct, or if you drink a lot of alcohol.
LFTs also look at the amount of bilirubin in the blood. This is a chemical in bile.
Bilirubin can be raised if you have a problem with your liver or gallbladder. Bilirubin can cause yellowing of your skin and eyes (jaundice).
LFTs also measure albumin. This is a protein in the blood that can be low in some types of cancer. You can also have low albumin if you’ve been eating small amounts and are malnourished.