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If you see your GP because you're concerned about symptoms of non-Hodgkin lymphoma, they'll ask about your health and may carry out a simple physical examination.

If necessary, your GP will refer you to hospital for further tests.

If you're referred to hospital, a biopsy will usually be carried out, as this is the only way to confirm a diagnosis of non-Hodgkin lymphoma.

A biopsy involves removing some or all of the swollen lymph node, which is then studied in a laboratory.

A biopsy is a small procedure or operation that can often be carried out under a local anaesthetic (where the area is numbed, but you're awake).

This may be performed by a radiologist using an ultrasound or CT scan, or as an operation by a surgeon.

In some cases, the swollen lymph node isn't easily accessible and a general anaesthetic may be required (where you're asleep).

A pathologist (an expert in the study of diseased tissue) will then check the tissue sample for the presence of cancerous cells.

If they find cancerous cells, they can also identify exactly which type of non-Hodgkin lymphoma you have, which is important for planning your treatment.

There are more than 30 types of non-Hodgkin lymphoma.

Macmillan Cancer Support has detailed information about the different types of non-Hodgkin lymphoma

If a biopsy confirms a diagnosis of non-Hodgkin lymphoma, further testing will be required to check how far the lymphoma has spread.

This allows a doctor to diagnose the stage of your lymphoma.

Further tests may include:

• blood tests – samples of blood will be taken throughout your diagnosis and treatment to check your general health, the levels of red and white cells and platelets in your blood, and how well organs such as your liver and kidney are working
• chest X-ray – this can check whether the cancer has spread to your chest or lungs
• bone marrow sample – another biopsy may be carried out to see if the lymphoma has spread to your bone marrow; this involves using a long needle to remove a sample of bone marrow from your pelvis and can be done using a local anaesthetic
• CT scan – this scan takes a series of X-rays that build up a 3D picture of the inside of the body to check the spread of the cancer 
• MRI scan – this scan uses strong magnetic fields to build up a detailed picture of areas of your body to check the spread of the cancer
• PET scan – this scan measures the activity of cells in different parts of the body, and can check the spread of the cancer and the impact of treatment; it's usually taken at the same time as a CT scan to show precisely how the tissues of different parts of the body are working
• lumbar puncture – using a thin needle, a sample of spinal fluid is taken and examined to see if it contains any lymphoma cells

When the testing is complete, it should be possible to determine the stage of your lymphoma. "Staging" means scoring the cancer by how far it's spread.

The main stages of non-Hodgkin lymphoma are:

• stage 1 – the cancer is limited to one group of lymph nodes, such as your neck, armpit or groin nodes, either above or below your diaphragm (the sheet of muscle underneath the lungs)
• stage 2 – 2 or more lymph node groups are affected, both either above or below, but just on one side of, the diaphragm
• stage 3 – the cancer has spread to lymph node groups on both sides of the diaphragm, above and below
• stage 4 – the lymphoma has spread beyond the lymphatic system and is now present in both lymph nodes and organs or bone marrow

Health professionals also add the letter "A" or "B" to your stage to indicate whether or not you have certain symptoms.

"A" is put after your stage if you have no additional symptoms other than swollen lymph nodes.

"B" is put after your stage if you have additional symptoms of weight loss, fever or night sweats.

In some cases, health professionals also use additional letters to indicate where the cancer first developed.

For example, "E" (extranodal) means the cancer developed outside the lymphatic system.

Your specialist care team will be able to explain in more detail what your test results mean.

Testing can also help health professionals decide the "grade" of the cancer.

There are 2 main grades of non-Hodgkin lymphoma:

• low-grade or indolent non-Hodgkin lymphoma is where the cancer grows slowly, and you may not experience any symptoms for many years
• high-grade or aggressive non-Hodgkin lymphoma is where the cancer grows quickly and aggressively

Low-grade tumours don't necessarily need immediate medical treatment, but are sometimes harder to completely cure.

High-grade lymphomas need to be treated immediately, but tend to respond much better to treatment and can often be cured.

In some cases, low-grade lymphomas can develop into high-grade lymphomas over time.

Read more about treating non-Hodgkin lymphoma.