Diagnosing an insulinoma

Insulinoma is a type of neuroendocrine tumour (NET) that starts in the insulin making cells of the pancreas. Insulinomas make the hormone insulin, which controls the blood sugar levels. So you might see your GP because of symptoms caused by changes in the levels of insulin.

Insulinomas are rare tumours. So your doctor might ask you to have tests that check for other conditions first.

Seeing your GP

You usually start by seeing your GP. They will ask you about your general health, symptoms and may also examine you.

Your GP might check your blood pressure, heart rate and temperature. They may arrange for you to have blood tests and check your blood sugar level. Your doctor will then decide if you need to see a specialist.

Referral to a specialist

Your GP looks at your symptoms and decides what specialist to refer you to. For example, they might refer you to an endocrinologist if you have problems with your blood sugar levels.

The specialist might ask you to have more tests. If tests show that you have an insulinoma, your specialist will refer you to a team of doctors and specialist nurses who have expertise in treating NETs.


You have tests to check:

  • whether you have a NET
  • the type of NET you have
  • the size of the tumour and whether it has spread

This helps your doctor plan your treatment.

Test to check your blood sugar level

You have this test if you have symptoms of low blood sugar. This is quick and easy. The doctor or nurse pricks your finger to get some of your blood. Then they put the blood into a blood sugar testing machine. 

If your blood sugar level is low (below 2.2 mmol per litre of blood), you have further blood tests to check the levels of insulin and other hormones in your blood. You may also have blood tests to check for proteins that stop the pancreas from making insulin.

A fasting test

A fasting test helps doctors diagnose insulinomas. You stay in hospital and have regular blood tests to check your blood sugar levels. 

The fasting test usually takes 72 hours (3 days). You can’t eat or drink anything except water. But your nurse monitors you regularly to look for signs of low blood sugar. 

CT scan

A CT scan can show up an insulinoma and see whether it has spread anywhere else in your body.

MRI scan

An MRI scan takes detailed pictures of your body. You might have an MRI scan to check whether the insulinoma has spread to other parts of the body such as the liver. 


This test looks at the inside of your food pipe, stomach and bowel. Your doctor uses a long flexible tube which has a tiny camera and a light on the end of it. Doctors can take samples of any abnormal areas (biopsies).

Endoscopic ultrasound scan (EUS)

This test combines an ultrasound and endoscopy to look at the inside of your food pipe, stomach, pancreas and bile ducts. 

Your doctor uses a long flexible tube (endoscope) with a tiny camera and light on the end. It also has an ultrasound probe. The ultrasound helps the doctor find areas that might be cancer. They then can take samples (biopsies) of any abnormal areas.

Radioactive scans

These are octreotide scans (or octreoscans) or gallium PET scans. You have an injection of a low dose radioactive substance, which is taken up by some NET cells. The cells then show up on the scan.

You may have other tests, depending on your symptoms. Your doctor can tell you which tests you need.
Last reviewed: 
02 Jul 2021
Next review due: 
02 Jul 2024
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    University Hospital Southampton NHS Foundation Trust, 2016

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    Annals of Oncology 2020, Vol 31, Issue 5 

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    Wolters Kluwer, 2019

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