Insulinoma

Learn about symptoms, causes, diagnosis and treatment, including how this rare pancreatic tumor causes low blood sugar.

Update Date: 09.09.2026

Overview
Symptoms
Causes
Risk factors
Complications
Diagnosis
Treatment
Preparing for an appointment

Overview

An insulinoma is a rare tumor that forms in the pancreas. It is a type of pancreatic neuroendocrine tumor. An insulinoma can occur at any age. But it is most often diagnosed in adults.

The pancreas makes insulin, a hormone that helps control blood sugar. Usually, the pancreas releases less insulin when blood sugar is low. An insulinoma keeps releasing insulin even when blood sugar is already low. This can cause blood sugar to drop too low, a condition called hypoglycemia.

About 90% of insulinomas are not cancerous. These are called benign insulinomas. About 10% of insulinomas are cancerous, also called malignant insulinomas. Cancerous insulinomas can spread beyond the pancreas.

Insulinomas can be serious because very low blood sugar can affect the brain and other parts of the body. Treatment can help. Surgery can cure many insulinomas. Cancerous insulinomas may need other treatments along with surgery.

Symptoms

Insulinoma symptoms happen when blood sugar drops too low. Symptoms often occur after going without food for several hours. Eating or drinking something that contains sugar may ease symptoms.

Symptoms may include:

  • Feeling weak or tired.
  • Sweating.
  • Headache.
  • Feeling hungry or nauseated.
  • Feeling lightheaded.
  • Confusion.
  • Anxiety and irritability.
  • Blurred vision.

Severe low blood sugar can cause seizures or loss of consciousness.

Over time, some people with an insulinoma gain weight. This may happen because they eat more often to stop or treat low blood sugar. High insulin levels also can contribute to weight gain.

When to seek care

Schedule an appointment with a healthcare professional if you have repeated symptoms of low blood sugar, and you don't know what is causing them.

When to seek emergency care

Severe low blood sugar needs immediate medical care. Seek emergency medical help if low blood sugar causes:

  • Seizures.
  • Loss of consciousness.
  • Severe confusion or trouble speaking, walking or responding to others.

Causes

It is not clear what causes most insulinomas. A small number of insulinomas are linked to inherited conditions. These conditions are caused by gene changes that can be passed from parents to children.

Risk factors

Most people with an insulinoma don't have a known risk factor. A small number of insulinomas are linked to inherited conditions, such as multiple endocrine neoplasia, type 1 (MEN 1). People with MEN 1 may develop more than one insulinoma. MEN 1 also raises the risk of other tumors.

Your healthcare team may recommend genetic counseling and testing if they think your insulinoma could be linked to an inherited condition.

Complications

Repeated episodes of low blood sugar can be serious. If blood sugar becomes very low, it can affect how the brain works and may lead to:

  • Seizures.
  • Loss of consciousness.
  • Coma.

Diagnosis

Diagnosing an insulinoma starts with finding out if your symptoms are caused by low blood sugar. Healthcare professionals look for three things, called Whipple triad:

  • You have symptoms of low blood sugar.
  • A blood test shows that your blood sugar is low when you have symptoms.
  • Your symptoms get better after you eat or drink something that raises your blood sugar.

Your healthcare professional asks about your symptoms, when they happen and what makes them better.

Blood tests

Your healthcare team may do several blood tests when your blood sugar is low. Tests may include:

  • Blood glucose test. This test measures the amount of sugar, called glucose, in your blood. It can confirm that your blood sugar is low.
  • Insulin test. This test measures the amount of insulin in your blood. A higher-than-expected insulin level when your blood sugar is low may be a sign of an insulinoma.
  • Proinsulin test. This test measures proinsulin, a substance the pancreas uses to make insulin.
  • C-peptide test. This test measures C-peptide, a substance released when the pancreas makes insulin. The test helps show whether the insulin in your blood comes from your pancreas.

The results from these tests can confirm whether your body is making too much insulin when your blood sugar is low.

You also may have blood tests to check for certain diabetes medicines. This can help show whether a medicine is causing your low blood sugar.

72-hour fasting test

You may have a supervised fasting test if your healthcare team needs to do blood tests while your blood sugar is low. The test can last up to 72 hours, but it often ends sooner.

During the test, you don't eat. Your healthcare team checks your blood sugar and watches for symptoms. When your blood sugar gets low enough, blood samples are taken for testing.

Imaging tests

If blood tests suggest that an insulinoma is causing low blood sugar, imaging tests can help find the tumor in the pancreas. Imaging tests can show the tumor's size and location. They also may show whether the insulinoma has spread beyond the pancreas.

Imaging tests may include:

  • CT scan. A computerized tomography (CT) scan uses X-rays to create detailed images of the pancreas and nearby areas.
  • MRI. Magnetic resonance imaging (MRI) uses a magnetic field and radio waves to create detailed images of the pancreas and nearby areas.
  • Endoscopic ultrasound. This test uses sound waves to create detailed images of the pancreas. A healthcare professional passes a thin, flexible tube with an ultrasound device on the end through the mouth and into the digestive tract. The ultrasound device can get close to the pancreas and can help find small insulinomas.
  • Positron emission tomography (PET) scan. A PET scan uses a small amount of a radioactive substance to make images of the insulinoma. PET scans may help find an insulinoma that is hard to locate, look for cancer that has spread or provide information that helps guide treatment.

Other tests

If imaging tests don't show where the insulinoma is, other tests may be needed. One option is a selective arterial calcium stimulation test. During this test, calcium is injected into different blood vessels that supply different parts of the pancreas. The calcium causes insulin-producing cells to release insulin. A healthcare professional takes blood samples to measure insulin. A rise in insulin can help show which part of the pancreas contains the insulinoma.

Genetic testing

Some people with an insulinoma may be referred for genetic testing. This testing can look for gene changes linked to inherited conditions, such as multiple endocrine neoplasia, type 1 (MEN 1). The results can help your healthcare team plan treatment and decide whether you may need screening for other tumors.

Checking for cancer

Most insulinomas are not cancerous. A cancerous insulinoma may be found before it has spread beyond the pancreas. A cancerous insulinoma that has spread to other parts of the body is called metastatic insulinoma. If imaging tests show that the insulinoma has spread to other parts of the body, that confirms it is cancerous.

Your healthcare team may advise a biopsy to learn more about the tumor. During a biopsy, a small piece of tissue or some cells are removed for testing in a lab. The results can help determine the tumor's grade. The grade provides information about how quickly the tumor may grow.

Treatment

Treatment for insulinoma depends on where the tumor is, whether it is cancerous and your overall health.

Surgery

Surgery is the main treatment for most insulinomas. When possible, the surgeon removes the tumor while leaving as much of the pancreas in place as possible. Surgery can cure most insulinomas that haven't spread.

The type of surgery depends on the tumor's size, where it is and how close it is to the pancreatic duct or major blood vessels.

Surgical options include:

  • Enucleation. The surgeon removes only the insulinoma, leaving the rest of the pancreas in place.
  • Partial pancreatectomy. The surgeon removes the part of the pancreas where the insulinoma is.
  • Whipple procedure. This surgery is not commonly needed for an insulinoma. It may be used when the tumor is deep in the head of the pancreas or close to the pancreatic duct or major blood vessels. The surgeon removes part of the pancreas and parts of nearby organs. The Whipple procedure also is called a pancreaticoduodenectomy.

After surgery

After surgery, your healthcare team checks your blood sugar. Your blood sugar may be high for a short time after the insulinoma is removed.

If part of your pancreas is removed, the remaining pancreas may not make enough insulin or digestive juices. This may lead to diabetes or trouble digesting food. You may need medicine to control your blood sugar or to help digest food.

Medicines

Medicines may be used to help prevent low blood sugar if surgery isn't possible or while waiting for surgery.

Some medicines reduce the amount of insulin released by the tumor. Others help control blood sugar.

Treatment for cancerous insulinomas

Cancerous insulinomas may need treatment in addition to surgery, especially if the cancer has spread. Surgery may be used to remove the insulinoma, cancer that has spread or both. Other treatments can help control the cancer.

Other treatments may include:

  • Chemotherapy. Chemotherapy treats cancer with strong medicines.
  • External beam radiation therapy. This treatment uses high-energy beams to treat cancer.
  • Peptide receptor radionuclide therapy. This treatment combines a medicine that targets cancer cells with a small amount of a radioactive substance.

Prognosis

A prognosis is the likely outcome of a condition. It includes your chances of recovery and what you may expect over time.

Noncancerous insulinomas

About 90% of insulinomas are not cancerous. Surgery to remove the tumor often cures the condition. Sometimes an insulinoma comes back after surgery. But this is not common.

Cancerous insulinomas

Cancerous insulinomas are more serious, especially if they have spread to other parts of the body. Treatment may help control the cancer.

Because cancerous insulinomas are rare, studies of survival have included only small numbers of people. This makes it hard to give one survival rate that applies to everyone. Survival rates for neuroendocrine tumors give information about these tumors as a group. But the rates aren't specific to insulinomas.

Your prognosis depends on many things. These include whether the cancer has spread, how fast it is growing, whether surgery is an option and how well the cancer responds to treatment. Your healthcare team can help you understand what these factors may mean for you.

Self-care

Changes to when and what you eat can help prevent low blood sugar. Your healthcare team may recommend these changes along with medicines or other treatments. A dietitian can help you find an eating plan that works for you.

Ways to help prevent low blood sugar include:

  • Eat regular meals and snacks. Try not to go too long without eating. Going without food can cause your blood sugar to drop.
  • Choose carbohydrates that take longer to digest. Examples include whole-grain bread, oatmeal and beans. These foods can help keep your blood sugar from dropping too fast.
  • Plan for low blood sugar at night. Your healthcare team can help you plan ways to prevent low blood sugar while you sleep. Some people may need a snack during the night.
  • Know how to treat low blood sugar. Keep a source of fast-acting sugar, such as glucose tablets or juice, nearby. Use it if your blood sugar gets too low.
  • Keep track of your blood sugar. Your healthcare professional may recommend checking your blood sugar at home. One way is with a blood glucose meter, which needs a small drop of blood from your finger. Another way is with a continuous glucose monitor (CGM). A CGM tracks your blood sugar throughout the day and night and can warn you if it gets too low. Ask your healthcare professional which type of blood sugar monitoring is right for you.

If you continue to have low blood sugar, tell your healthcare team. Medicines and other treatments also can help control low blood sugar.

Preparing for an appointment

Schedule an appointment with a doctor or other healthcare professional if you have repeated symptoms of low blood sugar. If your healthcare professional thinks you may have an insulinoma, you may be referred to a specialist.

Your care team may include:

  • An endocrinologist, a doctor who specializes in treating hormone conditions.
  • A surgeon who has experience with pancreas surgery.
  • An oncologist, a doctor who treats cancer, if the insulinoma is cancerous.
  • A genetic counselor if an inherited condition may be involved.

What you can do to prepare

When you make the appointment, ask if there's anything you need to do in advance, such as fasting before having a specific test. You also can:

  • Write down your symptoms, including when they happen and what seems to make them better or worse.
  • Write down any blood sugar readings you have. If you use a continuous glucose monitor, bring your glucose records with you.
  • Write down your family history of insulinoma, multiple endocrine neoplasia, type 1 (MEN 1) and other tumors involving the parathyroid or pituitary glands.
  • Make a list of all medicines, vitamins and supplements that you take and the doses.
  • Consider bringing a family member or friend. They can listen, take notes and help you remember information from the appointment.
  • Write down your questions. List the most important ones first.

Questions to ask your doctor

For insulinoma, some basic questions to ask your healthcare professional include:

About your diagnosis

  • What is likely causing my symptoms?
  • What tests do I need?
  • How should I prepare for these tests?
  • Where in my pancreas is the insulinoma?
  • Is the insulinoma cancerous?
  • Has the insulinoma spread beyond the pancreas?
  • Should I consider genetic counseling or testing?

About treatment and low blood sugar

  • What treatment options are available for me?
  • Is there one treatment you recommend over the others?
  • Will I need surgery? If so, what type?
  • What are the possible risks or side effects of the treatment you recommend?
  • What can I do to prevent low blood sugar while I wait for treatment?
  • How should I treat low blood sugar when it happens?
  • Should I check my blood sugar at home?

About follow-up and other concerns

  • How likely is the insulinoma to come back after treatment?
  • Will I need follow-up tests after treatment?
  • How might surgery affect how my pancreas works?
  • I have other health conditions. How can I manage them together?
  • What costs should I expect for the tests and treatment you recommend?
  • Are there resources where I can learn more about insulinoma?

What to expect from your doctor

Your healthcare professional may ask questions about your symptoms and health, such as:

  • When did your symptoms start?
  • How often do they happen?
  • How severe are your symptoms?
  • Do they happen after you haven't eaten for several hours?
  • Do they happen during the night or when you first wake up?
  • Does anything make your symptoms better or worse?
  • Does eating or drinking something with sugar make your symptoms better?
  • Have you checked your blood sugar when you have symptoms? If so, how low was it?
  • Have you ever lost consciousness, had a seizure or needed help from someone else because of low blood sugar?
  • Have you gained weight without trying?
  • Does anyone in your family have MEN 1, insulinoma, or other tumors of the parathyroid or pituitary glands?

© 2026 Mayo Foundation for Medical Education and Research. All rights reserved. Terms of Use