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Hypoglycaemia & Insulinoma: MRCP Guide

TL;DR

Hypoglycaemia is a high-yield topic in MRCP Part 1, frequently tested through biochemical interpretation and clinical scenarios. “Hypoglycemia: Investigation & Insulinoma” centres on confirming Whipple’s triad, interpreting insulin and C-peptide levels, and distinguishing endogenous from exogenous causes. The 72-hour fasting test remains the gold standard for insulinoma diagnosis. Mastering patterns rather than memorising facts is key to scoring well.


Why this matters

Hypoglycaemia is a core endocrine topic in MRCP Part 1, combining physiology, pharmacology, and clinical reasoning. It is frequently examined not as a recall question but through laboratory interpretation and clinical vignettes. Insulinoma, although rare, is a favourite exam condition because of its classic biochemical profile and diagnostic pathway.

For a structured preparation strategy, start with the MRCP Part 1 overview and integrate this topic within your endocrinology revision plan.


Core sections

1. Definition and Whipple’s Triad

Hypoglycaemia is clinically significant when plasma glucose is <3.0 mmol/L. However, diagnosis requires Whipple’s triad:

  1. Symptoms of hypoglycaemia

  2. Documented low plasma glucose

  3. Relief of symptoms after glucose administration

This triad prevents overdiagnosis based on isolated low readings.

2. Clinical Features: Early vs Late

  • Autonomic (adrenergic): sweating, tremor, palpitations, anxiety

  • Neuroglycopenic: confusion, visual disturbance, seizures, coma

Recurrent episodes may blunt autonomic warning symptoms—an important consideration in diabetics.

3. Causes of Hypoglycaemia

Category

Examples

Drug-induced

Insulin, sulfonylureas

Critical illness

Sepsis, hepatic failure

Hormonal deficiency

Addison’s disease, hypopituitarism

Endogenous hyperinsulinism

Insulinoma

Other

Alcohol, prolonged fasting

Exam tip: Drug-induced hypoglycaemia is the most common cause in real-world practice.

4. Initial Investigations

Investigations should be performed during a hypoglycaemic episode:

  • Plasma glucose

  • Insulin

  • C-peptide

  • Proinsulin

  • Beta-hydroxybutyrate

  • Sulfonylurea screen

MRCP questions typically provide these values together—interpretation is crucial.

5. Key Biochemical Patterns

Condition

Insulin

C-peptide

Interpretation

Insulinoma

High

High

Endogenous insulin excess

Exogenous insulin

High

Low

No endogenous secretion

Sulfonylurea use

High

High

Drug-induced

Starvation

Low

Low

Ketosis present

High-yield concept: C-peptide distinguishes endogenous from exogenous insulin.

6. The 72-Hour Fasting Test

The gold standard for diagnosing insulinoma:

  • Conducted under supervision

  • Serial glucose and insulin measurements

  • Terminated when hypoglycaemia occurs

A positive test shows:

  • Low glucose

  • Inappropriately elevated insulin and C-peptide

This confirms endogenous hyperinsulinism.

7. Insulinoma: Exam Essentials

  • Pancreatic neuroendocrine tumour

  • Usually benign

  • Causes fasting hypoglycaemia

Clinical clues:

  • Symptoms relieved by eating

  • Weight gain due to frequent carbohydrate intake

8. Imaging and Localisation

Once biochemical confirmation is established:

  • CT or MRI pancreas

  • Endoscopic ultrasound (most sensitive)

  • Selective arterial calcium stimulation (specialised)

Important: Imaging is not first-line—biochemistry precedes localisation.

9. Management Overview

  • Acute: oral or IV glucose

  • Definitive: surgical resection

  • Medical: diazoxide or octreotide (if not surgical candidate)

10. Exam-Focused Summary (Top 10 Points)

  1. Confirm Whipple’s triad

  2. Always measure insulin and C-peptide together

  3. Low C-peptide suggests exogenous insulin

  4. High C-peptide suggests endogenous production

  5. Perform sulfonylurea screen

  6. Use 72-hour fast to confirm diagnosis

  7. Insulinoma causes fasting hypoglycaemia

  8. Weight gain is a useful clue

  9. Imaging follows biochemical diagnosis

  10. Diazoxide is used in inoperable cases


Practical examples / mini-cases

MCQ Example

A 50-year-old man presents with recurrent morning confusion relieved by eating. Blood glucose is 2.3 mmol/L. Laboratory findings:

  • Insulin: elevated

  • C-peptide: elevated

  • Sulfonylurea screen: negative

What is the most likely diagnosis?

Answer: Insulinoma

Explanation :Elevated insulin with elevated C-peptide indicates endogenous insulin production. A negative sulfonylurea screen excludes drug-induced causes, confirming insulinoma.


Focused MRCP Part 1 study session with notes and timer for exam preparation

Common pitfalls (5 bullets)

  • Failing to confirm Whipple’s triad

  • Confusing reactive hypoglycaemia with fasting hypoglycaemia

  • Misinterpreting C-peptide levels

  • Assuming imaging is the first step

  • Overlooking sulfonylurea screening


FAQs

1. What is the first step in evaluating hypoglycaemia?

Confirm Whipple’s triad to ensure the hypoglycaemia is clinically relevant before proceeding with investigations.

2. How can insulinoma be differentiated from exogenous insulin use?

By measuring C-peptide—elevated in insulinoma and suppressed with exogenous insulin.

3. What is the gold standard test for insulinoma?

The supervised 72-hour fasting test demonstrating inappropriate insulin secretion during hypoglycaemia.

4. When should imaging be performed?

After biochemical confirmation of endogenous hyperinsulinism.

5. What is the most common cause of hypoglycaemia overall?

Drug-induced hypoglycaemia, particularly insulin and sulfonylureas.


Ready to start?

Strengthen your understanding with targeted practice using our Free MRCP MCQs or test your readiness with a Start a mock test. For a structured roadmap, revisit the MRCP Part 1 overview and complement this with endocrinology-focused revision posts.


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