This is where the number and appearance of the different blood cells in a sample of your blood are checked in a laboratory.
An abnormally high number of unusual white blood cells (lymphocytes) can be a sign of CLL. A detailed examination of these cells can usually confirm the diagnosis.
X-rays and scans
You may also have:
These tests can check for problems caused by CLL, such as swollen glands or a swollen spleen, and help rule out other possible causes of your symptoms.
Bone marrow biopsy
Sometimes the haematologist may recommend removing a sample of your bone marrow (bone marrow biopsy) so they can examine it under a microscope to check it for cancerous cells.
The sample is removed using a needle inserted into your hip bone. Local anaesthetic is normally used to numb the area where the needle is inserted, although you may experience some discomfort during the biopsy.
The procedure will last around 15 minutes and you should not need to stay in hospital overnight. You may have some bruising and discomfort for a few days afterwards.
Lymph node biopsy
In some cases, removing and examining a swollen lymph gland can help confirm a diagnosis of CLL. This is known as a lymph node biopsy.
The gland is removed during a minor operation carried out under either local or general anaesthetic, where you're asleep. You will not usually need to stay in hospital overnight.
After the operation, you'll be left with a small wound that will be closed with stitches.
Tests may also be carried out on your blood and bone marrow samples to check for any unusual genes in the cancerous cells.
Identifying unusual genes in these cells can help your doctors decide how soon you should start treatment and which treatment is best for you.
Some treatments for CLL do not work as well in people with certain abnormal genes in the affected cells.