Insulinoma Explained

An insulinoma is a rare, usually benign tumour of the pancreas that makes too much insulin. Because insulin lowers blood sugar, the surplus can cause episodes of low blood sugar, often when fasting or after exercise. Diagnosis relies on carefully timed blood tests, sometimes during a supervised fast, followed by imaging.

What an insulinoma is

The pancreas contains clusters of hormone-making cells called the islets of Langerhans. Among them, beta cells produce insulin, the hormone that helps move glucose from the blood into cells and keeps blood sugar within a healthy range. An insulinoma is a tumour of these insulin-making cells that releases insulin without responding normally to the body's signals.

Normally, insulin release falls when blood sugar is low so that levels can recover. An insulinoma keeps releasing insulin even when blood sugar has dropped, which drives glucose too low. Most insulinomas are small and benign, meaning they do not spread, although a smaller number can behave more aggressively, which is one reason careful evaluation is important.

Common signs and symptoms

Symptoms reflect low blood sugar (hypoglycaemia) and the body's response to it. They often appear when a person has not eaten for a while or after physical activity, and may ease after eating. They can include:

• Shakiness, sweating, or a pounding heartbeat
• Hunger, especially between meals or overnight
• Confusion, difficulty concentrating, or changes in behaviour
• Blurred vision, dizziness, or weakness
• In more severe episodes, fainting or seizures

What causes it

In most people no specific reason for an insulinoma is found, and these tumours typically arise on their own. In a minority of cases an insulinoma is linked to an inherited syndrome that predisposes a person to several kinds of endocrine tumours. Because of this, a clinician may ask about family history of similar tumours and, in selected cases, consider genetic counselling.

How it is diagnosed

Diagnosing an insulinoma involves demonstrating that low blood sugar occurs alongside inappropriately high insulin, then locating the tumour. Common steps include:

• Supervised fasting test — under medical observation, blood is sampled over time to capture a low-blood-sugar episode and the hormone levels at that moment.
• Blood glucose and insulin — measured together so a clinician can see whether insulin is high when glucose is low.
• Related markers — substances made alongside insulin, such as C-peptide, help show that the insulin is coming from the body rather than an outside source.
• Imaging — once biochemical tests point to an insulinoma, scans of the pancreas help locate the tumour.

For background on the relevant tests, see our blood tests and hormones sections, and our conditions overview for related topics.

How it is generally managed

Management is decided with a specialist team. For many people, the main treatment is surgery to remove the tumour, which can resolve the episodes of low blood sugar. Before surgery or when surgery is not suitable, clinicians may use measures to reduce low-blood-sugar episodes, such as adjustments to eating patterns or specific medicines, always under medical guidance. When an inherited syndrome is involved, longer-term monitoring is common. General treatment principles are outlined in our treatments section. This page is educational and is not a substitute for personalised medical advice.