How Insulinoma Is Diagnosed

Insulinoma is a type of tumor that develops on the pancreas and usually isn’t cancerous. It causes the pancreas to release higher-than-normal levels of the hormone insulin. This hormone regulates blood sugar levels and helps move glucose from the bloodstream into cells, where it is used for energy.

Too much insulin can cause blood sugar to drop to dangerously low levels. In this article, we'll review the diagnostic process for an insulinoma, which usually includes blood tests and imaging of the pancreas.

Doctors explaining lab results to patient


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At-Home Testing

There isn’t an at-home test that can diagnose an insulinoma, and a diagnosis usually takes time to come about.

If you’re regularly experiencing symptoms of low blood sugar, your healthcare provider may ask you to check your blood sugar levels at home using a glucometer before your appointment. These tests, available over the counter at drugstores, indicate your blood glucose levels, allowing you to monitor for low levels at home.

Recognizing Hypoglycemia

Hypoglycemia, or low blood sugar, can be very dangerous if your levels get too low. It’s important to know the signs of low blood sugar so that you can reach a healthy level.

Symptoms of low blood sugar include:

  • Vision changes, like double or blurred vision
  • Confusion
  • Anxiety or mood changes
  • Sweating
  • Weakness
  • Tremors
  • Dizziness

Extremely low blood sugar may cause:

  • Loss of consciousness or coma
  • Rapid heart rate
  • Seizures

Very low blood sugar can even lead to death in some cases. If you notice symptoms of hypoglycemia, it’s important to immediately consume a food or drink with sugar, like juice or fruit snacks. Also, discuss these symptoms with your healthcare provider.

Physical Examination

A physical exam is usually the first step toward diagnosis. Your healthcare provider will review vitals—like blood pressure and heart rate—and look for any physical signs of a health condition. They will ask questions about your symptoms, medical history, and family history of medical conditions.

A physical exam alone may not be enough to diagnose a condition like insulinoma. Historically, healthcare providers have diagnosed insulinoma using criteria from the Whipple’s triad, a set of three signs that suggest symptoms of hypoglycemia.

The three criteria in the Whipple’s triad include:

  • Hypoglycemia, blood glucose below 50 milligrams per deciliter
  • Symptoms of low blood sugar, such as dizziness, weakness, drowsiness, confusion, seizures, and coma
  • Symptoms that improve after being given sugar (glucose)

These criteria are still used for screening, but other tests are needed to confirm a diagnosis.

Labs and Tests

The current gold standard, or best practice, for diagnosing insulinoma is monitoring blood work during a 72-hour fast. Here are some examples of labs that will be monitored during your 72-hour fast:

  • Beta-hydroxybutyrate
  • Blood glucose
  • C-peptide
  • Insulin
  • Proinsulin
  • Sulfonylurea

Changes in these lab values are used to determine if an insulinoma or another condition is causing your symptoms. You’ll stay in the hospital while you fast so your healthcare team can closely monitor changes in your blood sugar levels. They will also correct your blood sugar if it gets dangerously low.

During the fast, you’ll only be allowed to drink water. Your healthcare team will measure your blood sugar and other labs at least every six hours.

Usually, you’ll experience low blood sugar levels within 48 hours after starting the fast if you have an insulinoma. Although, some rare types of insulinoma may only secrete extra insulin after a meal.

Imaging

Imaging tests are used to view the size and location of an insulinoma. Typically, insulinoma is treated by removing the tumor during surgery. Imaging tests help your healthcare provider prepare for treatment.

Your healthcare provider may order tests such as:

  • Abdominal ultrasound: An ultrasound uses sound waves to produce an image of a body part. Sometimes an ultrasound is done early in the diagnostic process because it has a lower cost and tends to be more convenient than other tests.
  • Computed tomography (CT) scan: A computer compiles images from multiple X-rays to form a more detailed picture of the organ from different angles. The scan will likely be ordered with contrast, meaning a dye will be injected into your veins to better view the tumor. CT scans can detect about 75% of insulinomas.
  • Endoscopic ultrasonography (EUS): An EUS is a more invasive exam than the other imaging options. Typically, it’s done when an insulinoma is suspected but hasn’t appeared on other imaging tests. In this procedure, a special endoscope (a thin tube with a camera attached) that uses high-frequency sound waves to produce detailed images is inserted into the body. An upper EUS is used to assess the pancreas.
  • Magnetic resonance imaging (MRI): An MRI uses magnetic fields to create a picture of part of your body. MRIs can detect about 85% of insulinomas.

Differential Diagnosis

Low blood sugar can be caused by multiple conditions. When your healthcare provider is assessing you for an insulinoma, the doctor will also rule out other conditions, such as:

  • Insulin autoimmune hypoglycemia: This rare autoimmune condition is caused by the body signaling the immune system to attack the hormone insulin.
  • Noninsulinoma pancreatogenous hypoglcemia syndrome (NIPHS): NIPHS is a rare condition that causes low blood sugar levels due to too much insulin, which isn’t caused by an insulinoma tumor.
  • Non–islet cell tumors: These rare tumors can be benign or malignant. The tumors produce insulin-like growth factors (IGF) that cause low blood sugar.
  • Post–gastric bypass hypoglycemia: Some people experience frequent low blood sugar levels following gastric bypass surgery.
  • Sulfonylurea-induced hypoglycemia: Sulfonylurea is sometimes used to help treat diabetes. Too large of a dose of medication or not eating enough food can cause low blood sugar.

A Word From Verywell

An insulinoma is a rare type of tumor that forms on the pancreas. It can take time to get a diagnosis of insulinoma. Typically, blood work and imaging tests will be done to confirm the diagnosis.

If you’re experiencing low blood sugar episodes, you may be asked to test your blood sugar at home. Keeping sugary snacks nearby can help to raise blood glucose levels back to a healthy level.

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2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Zhuo F, Anastasopoulou C. Insulinoma. In: StatPearls. StatPearls Publishing; 2021.

  2. Okabayashi T, Shima Y, Sumiyoshi T, et al. Diagnosis and management of insulinoma. World J Gastroenterol. 2013;19(6):829-837. doi: 10.3748/wjg.v19.i6.829