# Insulinoma

Confirm endogenous hyperinsulinemic hypoglycemia before imaging, then localize and stage for parenchyma-sparing cure when feasible. Persistent or metastatic disease requires continuous hypoglycemia prevention and multidisciplinary tumor-directed therapy selected by resectability and receptor imaging.

**Clinical question:** How should physicians confirm, localize, and treat insulinoma while preventing recurrent hypoglycemia?

Updated: 2026-09-16T00:25:58.812297+00:00

## What matters in practice
- Obtain a critical sample during documented hypoglycemia before localization: glucose, insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and sulfonylurea/meglitinide testing distinguish endogenous hyperinsulinism from exogenous insulin or secretagogue exposure. [16]
- A supervised fast is indicated when a spontaneous critical sample is unavailable; glucose below 55 mg/dL with insulin at least 3 µU/mL, C-peptide at least 0.6 ng/mL, proinsulin at least 5 pmol/L, beta-hydroxybutyrate no more than 2.7 mmol/L, and a negative secretagogue screen supports endogenous hyperinsulinemic hypoglycemia. [14][21]
- After biochemical confirmation, use pancreas-protocol CT for initial localization and metastatic assessment; add EUS or MRI for localized disease and GLP-1 receptor PET when conventional studies are unrevealing. [13][22]
- Solitary localized insulinoma is generally managed with curative surgical excision; operative strategy depends on anatomic localization and whether enucleation can preserve pancreatic parenchyma. [13][20][22]
- Do not assume somatostatin receptor imaging will exclude insulinoma: more than 50% may be missed by somatostatin receptor scintigraphy because receptor density is often low. [9]
- Metastatic or unresectable disease requires both glucose-directed therapy and tumor control; somatostatin receptor ligand therapy, everolimus, and peptide receptor radionuclide therapy are options selected by tumor biology and receptor expression. [3][8][22]

## Confirm the biochemical diagnosis before pancreatic imaging

A pancreatic lesion is not diagnostic without a contemporaneous hypoglycemic critical sample.

Evaluate patients with Whipple triad or recurrent fasting neuroglycopenia by drawing plasma glucose, insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and a sulfonylurea/meglitinide screen during spontaneous hypoglycemia. Give glucagon 1 mg IV after the specimen is collected; a plasma glucose rise greater than 25 mg/dL supports hyperinsulinemic hypoglycemia. [16]

At plasma glucose below 55 mg/dL, insulin of at least 3 µU/mL, C-peptide of at least 0.6 ng/mL, proinsulin of at least 5 pmol/L, beta-hydroxybutyrate no more than 2.7 mmol/L, and a negative sulfonylurea screen support endogenous hyperinsulinemic hypoglycemia. These results establish the physiologic syndrome requiring localization; they do not by themselves prove a pancreatic insulinoma. [14][21]

A low C-peptide in the setting of detectable insulin redirects the evaluation toward exogenous insulin exposure. Detectable sulfonylurea or meglitinide redirects management toward secretagogue-associated hypoglycemia rather than tumor localization. Suppressed ketogenesis, reflected by beta-hydroxybutyrate below 2.7 mmol/L, is a key discriminator of insulin-mediated hypoglycemia. [15][16]

*Critical-sample interpretation for suspected insulin-mediated hypoglycemia. [14][16][21]*

| Finding during hypoglycemia | Interpretation | Immediate next step |
| --- | --- | --- |
| Glucose <55 mg/dL, insulin ≥3 µU/mL, C-peptide ≥0.6 ng/mL, proinsulin ≥5 pmol/L, beta-hydroxybutyrate ≤2.7 mmol/L, negative secretagogue screen [14][21] | Endogenous hyperinsulinemic hypoglycemia [14][21] | Proceed to pancreatic localization and staging. [13][22] |
| Insulin present with low C-peptide [16] | Exogenous insulin effect is favored. [16] | Investigate insulin exposure; do not attribute the episode to insulinoma without further evidence. [16] |
| Sulfonylurea or meglitinide detected [16] | Insulin secretagogue-associated hypoglycemia [16] | Address medication or covert exposure; pancreatic localization is not the initial next step. [16] |
| Beta-hydroxybutyrate ≥2.7 mmol/L [15][16] | Insulin-mediated suppression of ketogenesis is not supported. [15][16] | Reassess non-insulin-mediated causes of hypoglycemia. [15] |

## Use a supervised fast when no spontaneous critical sample is available

The 72-hour fast remains the reference test for suspected fasting insulinoma.

Perform a monitored fast when the clinical history is compelling but an episode has not been captured. Permit noncaloric, caffeine-free beverages; measure glucose, insulin, and C-peptide at baseline and every 4 to 6 hours. Once plasma glucose falls below 60 mg/dL, increase sampling to every 1 to 2 hours with close observation. [16]

Terminate the fast when neuroglycopenic symptoms occur with plasma glucose below 45 mg/dL; the Endocrine Society threshold cited in Endotext is below 55 mg/dL. At termination, obtain glucose, insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and an oral insulin secretagogue screen before treating hypoglycemia. [16]

Most patients with insulinoma develop symptomatic hypoglycemia before the full 72 hours: approximately one-third by 12 hours, 80% by 24 hours, and 90% by 48 hours. A negative or non-diagnostic fast should prompt reconsideration of the event phenotype, particularly postprandial rather than fasting hypoglycemia, before pursuing invasive localization. [21]
- Do not order CT, MRI, EUS, or receptor PET as the first diagnostic step when endogenous hyperinsulinism has not been demonstrated; incidental pancreatic lesions can misdirect management. [13][14]
- Continue usual waking activity during the fast when safe, because activity may facilitate diagnostic hypoglycemia. [16]

## Localize only after biochemical confirmation and stage before surgery

Imaging determines resectability and the safest parenchyma-preserving operation.

Begin with contrast-enhanced CT to localize the pancreatic lesion and determine whether metastatic disease is present. For an apparently indolent localized lesion, use EUS or MRI as the next anatomic study when CT is negative or insufficient for procedural planning. Approximately 30% of insulinomas are smaller than 1 cm, making localization technically challenging. [13][22]

When CT, MRI, and EUS do not identify a lesion in biochemically proven endogenous hyperinsulinism, obtain GLP-1 receptor PET/CT or PET/MRI for occult, localized insulinoma. This modality is described as highly sensitive for indolent localized lesions and can avoid blind pancreatic resection. [13][22]

Somatostatin receptor imaging has a different role. Gallium-68 somatostatin analogue PET/CT is the most sensitive modality for pNET and NET localization broadly and is recommended for surgical candidates and advanced disease staging, but conventional somatostatin receptor scintigraphy frequently misses insulinomas because of lower receptor density. A negative somatostatin receptor study therefore should not end the localization workup for a suspected small localized insulinoma. [9][12]

If noninvasive studies remain negative despite unequivocal endogenous hyperinsulinemic hypoglycemia, refer to a high-volume pancreatic NET center for specialized localization and operative planning. Intraoperative palpation and intraoperative ultrasonography are important adjuncts, particularly when preoperative imaging is incomplete. [4][20]

### When to assess for MEN1

Consider MEN1 in patients with multiple pancreatic lesions, recurrent or metachronous insulinomas, or personal evidence of primary hyperparathyroidism or pituitary tumor. Approximately 4% of patients with insulinoma have MEN1, and multiple lesions are particularly associated with MEN1. [10][13]

*Localization strategy after biochemical confirmation of endogenous hyperinsulinemic hypoglycemia. [9][12][13][22]*

| Clinical setting | Preferred next study | Decision consequence |
| --- | --- | --- |
| Initial localization and metastatic assessment | Contrast-enhanced CT [13][22] | Defines visible pancreatic lesion, liver or other metastatic disease, and operative pathway. [13][22] |
| CT-negative or incompletely characterized presumed localized disease | EUS or MRI [13][22] | Improves localization for enucleation versus pancreatic resection planning. [13] |
| Biochemically proven disease occult on conventional imaging | GLP-1 receptor PET/CT or PET/MRI [13][22] | Targets occult indolent localized insulinoma for definitive surgery. [13][22] |
| Advanced disease or surgical staging of NET extent | Gallium-68 somatostatin analogue PET/CT [12] | Defines somatostatin receptor expression and whole-body disease burden; a negative result does not exclude insulinoma. [9][12] |

## Prevent recurrent hypoglycemia while localization and definitive therapy proceed

Recurrent neuroglycopenia requires active glucose prevention, not outpatient observation alone.

Patients with frequent fasting hypoglycemia, impaired awareness, seizures, or altered consciousness need immediate carbohydrate rescue and monitored glucose support while the critical sample and localization pathway are completed. During operative care, use perioperative glucose monitoring to detect and prevent hypoglycemia. [2][24]

For persistent hypoglycemia when surgery is delayed, contraindicated, or noncurative, use dietary measures and medical therapy to reduce hypoglycemia burden. Somatostatin receptor ligands may be used for hypoglycemia control, but therapeutic selection should account for receptor imaging and clinical response rather than presuming uniform benefit. [22][3]

Continuous glucose monitoring can provide practical surveillance in patients with recurrent or poorly perceived hypoglycemia, particularly during medical bridging or advanced disease management; it complements but does not replace laboratory confirmation of endogenous hyperinsulinism. [3]
- Escalate to inpatient management when recurrent neuroglycopenia cannot be reliably prevented with oral intake or when intravenous glucose is repeatedly required. [2][24]
- Avoid delaying definitive tumor assessment solely because interim glucose-directed measures reduce symptoms; durable cure for a resectable localized insulinoma is surgical. [13][22]

## Resect localized insulinoma with a pancreas-preserving strategy when feasible

The operative objective is cure of hypoglycemia while minimizing loss of pancreatic tissue.

Offer surgery for a solitary localized insulinoma after biochemical confirmation and conclusive localization. Surgical excision is the treatment of choice and is generally curative for localized pancreatic insulinoma. Select enucleation when lesion location permits safe parenchymal preservation; use partial pancreatectomy when anatomy precludes enucleation or requires formal resection. [13][20][22]

Use preoperative lesion location to choose minimally invasive, robot-assisted, or open surgery and to plan enucleation versus partial pancreatectomy. Intraoperative ultrasound and palpation can confirm lesion position and relationship to the pancreatic duct, particularly for small or occult tumors. [13][20]

Counsel patients about pancreatic morbidity when selecting the operative approach. In one three-decade surgical series, pancreatic fistula occurred in 44%, severe complications in 30%, overall morbidity in 72%, and mortality in 6%; these outcomes reflect a reported surgical cohort and reinforce the importance of experienced multidisciplinary pancreatic surgery. [5]

Pathology should document neuroendocrine differentiation with chromogranin A and synaptophysin immunostaining plus insulin staining; determine mitotic index and Ki-67 for grading and apply current WHO TNM classification. [9][14]

### Postoperative surveillance

After R0 resection of a benign sporadic solitary G1-G2 insulinoma, obtain a follow-up assessment at 3 to 6 months; recurrent imaging is not routinely proposed unless symptoms recur. Measure chromogranin A only if it was elevated initially. [20]
- Recurrent fasting hypoglycemia after surgery warrants repeat biochemical confirmation and renewed localization rather than assuming postoperative recurrence from symptoms alone. [16][20]

## Treat unresectable or metastatic insulinoma with parallel glucose and tumor control

Metastases establish malignant behavior and shift management from cure by local excision to multidisciplinary disease control.

Assess resectability and metastatic burden with cross-sectional and receptor-based imaging before selecting therapy. For aggressive malignant disease, management may combine debulking procedures, somatostatin receptor ligand therapy, everolimus, and peptide receptor radionuclide therapy; selection depends on disease extent, clinical hypoglycemia, and somatostatin receptor expression. [22]

Consider peptide receptor radionuclide therapy in metastatic or inoperable disease, particularly when somatostatin receptor expression is demonstrated. A contemporary review describes PRRT as a first-line approach alongside somatostatin analogues for metastatic or inoperable insulinoma because it can improve progression-free survival and provide durable improvement in hypoglycemia; the strength of evidence is limited by the rarity of the disease. [3]

Everolimus has produced rapid glycemic responses in metastatic insulinoma, including plasma glucose normalization within 14 days in a small report, and should be considered in refractory hypoglycemia when tumor-directed systemic therapy is needed. Sirolimus improved glycemic control in four infants with diffuse hyperinsulinemic hypoglycemia unresponsive to diazoxide and octreotide, but that pediatric experience should not be extrapolated as standard adult insulinoma therapy. [1]

For liver-dominant metastatic disease with refractory hypoglycemia, liver-directed therapy may be considered within a NET multidisciplinary program. A reported case of unresectable malignant insulinoma with liver metastases had hypoglycemia resolution after four courses of lutetium-177 dotatate PRRT, following incomplete response to long-acting octreotide and everolimus. [8]
- Obtain somatostatin receptor imaging before considering receptor-targeted PRRT; higher somatostatin receptor expression supports this strategy. [8][12]
- Continue close glucose monitoring during systemic or radionuclide therapy because symptomatic benefit and antitumor response may not occur synchronously. [3][8]

*Treatment direction for noncurable insulinoma. [3][8][22]*

| Clinical branch | Management direction | Selection discriminator |
| --- | --- | --- |
| Resectable localized disease | Curative surgical excision, favoring parenchyma preservation when technically feasible. [13][20][22] | Solitary localized lesion with operative candidacy. [13][22] |
| Unresectable or metastatic disease with hypoglycemia | Dietary and glucose-directed support plus somatostatin receptor ligand therapy and tumor-directed treatment. [3][22] | Symptom burden, tumor extent, and treatment response. [3][22] |
| Somatostatin receptor-positive metastatic or inoperable disease | Consider PRRT with lutetium-177 dotatate in a NET multidisciplinary program. [3][8] | Demonstrated receptor expression on somatostatin receptor imaging. [8][12] |
| Refractory metastatic hypoglycemia requiring systemic control | Consider everolimus as tumor- and glucose-directed therapy. [1][22] | Persistent hypoglycemia despite initial measures and need for systemic disease control. [1][22] |

## Common questions

### Does a negative somatostatin receptor scan exclude insulinoma?

No. Insulinomas often have low somatostatin receptor density, and more than 50% may be missed by somatostatin receptor scintigraphy. In biochemically proven disease with unrevealing CT, MRI, and EUS, proceed to GLP-1 receptor PET/CT or PET/MRI for occult localized lesions. [9][13][22]

## References
1. Sirolimus Therapy in Infants with Severe Hyperinsulinemic Hypoglycemia | New England Journal of Medicine — www.nejm.org — https://www.nejm.org/doi/full/10.1056/NEJMoa1310967
2. Insulin Blood Level - an overview | ScienceDirect Topics — www.sciencedirect.com — https://www.sciencedirect.com/topics/immunology-and-microbiology/insulin-blood-level
3. Managing Hypoglycaemia in Patients With Insulinoma—A Tertiary Centre Experience and Review of the Literature - Howarth - 2025 - Clinical Endocrinology - Wiley Online Library — onlinelibrary.wiley.com — https://onlinelibrary.wiley.com/doi/full/10.1111/cen.15188
4. The surgical management of insulinomas in children - ScienceDirect — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S0022346813003989
5. Surgical management of insulinoma over three decades — www.sciencedirect.com — https://www.sciencedirect.com/science/article/pii/S1365182X21001131
6. Effect of octreotide on plasma concentrations of glucose, insulin, glucagon, growth hormone, and cortisol in healthy dogs and dogs with insulinoma - ScienceDirect — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S0034528805000597
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9. ENETS Consensus Guidelines for the Management of Patients with Digestive Neuroendocrine Neoplasms: Functional Pancreatic Endocrine Tumor Syndromes — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC3701449
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12. Consensus guidelines update for the management of functional p-NETs (F-p-NETs) and non-functional p-NETs (NF-p-NETs) — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC4849884
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19. Management of Intractable Hypoglycemia With Yttirum-90 Radioembolization in a Patient With Malignant Insulinoma - ScienceDirect — www.sciencedirect.com — https://www.sciencedirect.com/science/article/abs/pii/S0002962915314592
20. Changes in diagnosis and operative treatment of insulinoma over two decades - PMC — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC10310606
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22. Approach to the Patient: Insulinoma - PMC — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC10940262
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## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.