PLAB 1 Endocrinology Questions: 10 Free Practice MCQs
Ten PLAB 1-style endocrinology questions with the answer and the reasoning behind it. They come from the UK.med bank, which has 34 endocrinology questions and many more across every topic.
1 / 10
A 12-year-old boy has hyperglycaemia, ketonaemia and positive antibodies against pancreatic islet antigens. Endogenous insulin production is very low.
Which mechanism best accounts for his low insulin production?
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Answer: D. Immune mediated destruction of pancreatic beta cells
Why: Autoimmune destruction of pancreatic beta cells leads to severe insulin deficiency in type 1 diabetes. The islet autoantibodies support this mechanism; obesity related insulin resistance does not explain the presentation.
- A. Alpha cells produce glucagon, and their failure does not explain autoimmune insulin deficiency.
- B. Thyroid disease can coexist with type 1 diabetes but does not cause beta cell destruction.
- C. Insulin resistance is not the primary process in this antibody positive presentation.
Sources: NICE NG18, Diabetes in children and young people
2 / 10
A 45-year-old female with known Addison's disease is brought to the emergency department. She has been suffering from gastroenteritis with severe vomiting for 48 hours. On examination, she is drowsy and has a blood pressure of 80/40 mmHg.
What is the most urgent pharmacological intervention required?
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Answer: B. Intravenous Hydrocortisone 100mg and IV fluid resuscitation
Why: Adrenal crisis is treated with immediate bolus injection of 100mg IV Hydrocortisone, followed by continuous infusion or regular QDS boluses, alongside rapid infusion of 0.9% normal saline. Mineralocorticoid replacement (fludrocortisone) can be withheld during acute resuscitation as high-dose hydrocortisone has cross-reactivity at aldosterone receptors.
- A. Oral treatment is contraindicated due to persistent vomiting. Fludrocortisone is not needed in the acute phase as high-dose hydrocortisone provides sufficient mineralocorticoid activity.
- C. Hydrocortisone is preferred over dexamethasone in adrenal crisis due to its mineralocorticoid action. Dexamethasone is only used if an ACTH stimulation test is planned immediately.
- D. Adrenaline is the treatment for anaphylaxis, not Addisonian crisis.
Sources: Society for Endocrinology guidelines
3 / 10
A 45-year-old woman is diagnosed with Graves' disease. She is started on Carbimazole.
What is the most serious side effect she needs to be urgently warned about?
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Answer: D. Agranulocytosis
Why: Carbimazole can cause agranulocytosis (neutropenia). Patients must be educated to seek medical attention if they develop symptoms of infection like sore throat or fever.
- A. Weight gain may occur as metabolism normalises, but it is not an emergency.
- B. Palpitations are a symptom of the disease, not a side effect of Carbimazole.
- C. Alopecia can occur but is not life-threatening.
Sources: BNF Carbimazole
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4 / 10
A 12-year-old boy presents with polyuria, polydipsia and weight loss. Testing confirms type 1 diabetes mellitus; autoantibodies to pancreatic islet antigens are present.
What mechanism causes the insulin deficiency in type 1 diabetes?
Show answer
Answer: B. Immune mediated destruction of pancreatic beta cells
Why: Type 1 diabetes is caused by immune mediated destruction of pancreatic beta cells, leading to insulin deficiency. This differs from the insulin resistance that is prominent in type 2 diabetes.
- A. Insulin resistance is central to type 2 diabetes and does not explain islet autoantibodies.
- C. Alpha cells produce glucagon, and their excess does not cause the defining insulin deficiency.
- D. Insulin receptor defects cause rare severe insulin resistance rather than autoimmune type 1 diabetes.
Sources: NICE NG17, Type 1 diabetes in adults; NICE NG18, Diabetes in children and young people
5 / 10
A 12-year-old boy is diagnosed with type 1 diabetes mellitus. He presents to the clinic with a 2-week history of polyuria, polydipsia, and weight loss. His random blood glucose level is 22 mmol/L.
What is the underlying mechanism for this patient's condition?
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Answer: A. Autoimmune destruction of pancreatic beta cells
Why: Type 1 diabetes mellitus is caused by autoimmune destruction of pancreatic beta cells, leading to a deficiency of insulin production. This results in hyperglycaemia and the symptoms presented by the patient.
- B. This is incorrect as the patient has type 1 diabetes mellitus, which is not caused by genetic mutation leading to insulin resistance.
- C. This is incorrect as the patient has type 1 diabetes mellitus, which is not caused by pancreatic alpha cell dysfunction.
- D. This is incorrect as the patient has type 1 diabetes mellitus, which is not caused by hormonal imbalance leading to hyperglycaemia.
Sources: NICE Guideline NG28
6 / 10
A 19-year-old female with type 1 diabetes is admitted to the emergency department. She is lethargic and breathing deeply. Lab results show: capillary blood glucose 24 mmol/L, blood ketones 4.2 mmol/L, venous pH 7.15, and bicarbonate 12 mmol/L. She is taking insulin glargine once daily at night.
What is the recommended initial insulin infusion rate and what should be done with her long-acting basal insulin?
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Answer: A. Commence fixed-rate intravenous insulin infusion (FRIII) at 0.1 units/kg/hour, and continue her usual long-acting basal insulin
Why: The Joint British Diabetes Societies (JBDS) guidelines for the management of DKA state that treatment should include: (1) Intravenous fluid resuscitation (0.9% sodium chloride). (2) Fixed-rate intravenous insulin infusion (FRIII) at 0.1 units/kg/hour. (3) Continuation of long-acting basal insulin (e.g. Glargine or Detemir) to maintain background control. (4) Monitoring and replacement of potassium (insulin shifts potassium intracellularly, causing rapid serum drops).
- B. Variable-rate insulin (sliding scale) is not recommended for the initial management of DKA; a fixed-rate infusion (0.1 units/kg/hour) is required to suppress ketogenesis. Basal insulin should never be stopped in T1DM.
- C. DKA is a medical emergency that requires immediate intravenous insulin and fluids. Subcutaneous insulin is insufficient due to poor perfusion and delayed absorption.
- D. An insulin infusion rate of 0.5 units/kg/hour is too high and increases the risk of rapid glucose drops, hypokalaemia, and cerebral oedema. The standard rate is 0.1 units/kg/hour.
Sources: JBDS-IP Guidelines for the Management of Diabetic Ketoacidosis
7 / 10
An 82-year-old man with type 2 diabetes is admitted with confusion and severe dehydration. Lab results show: capillary blood glucose 48 mmol/L, serum osmolality 360 mOsm/kg, venous pH 7.38, bicarbonate 24 mmol/L, and blood ketones 0.5 mmol/L.
What is the primary goal of initial fluid resuscitation, and how does the use of insulin differ from DKA?
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Answer: B. Gradual fluid resuscitation with 0.9% sodium chloride to reduce serum osmolality slowly (by 3-5 mOsm/kg/hour); do not start insulin immediately unless blood glucose stops falling with fluids alone
Why: Hyperosmolar Hyperglycaemic State (HHS) is characterized by severe hyperglycaemia (>30 mmol/L), high serum osmolality (>320 mOsm/kg), and absence of significant ketosis/acidosis. According to JBDS guidelines, treatment focuses on cautious rehydration with 0.9% NaCl (aiming to reduce osmolality by 3-5 mOsm/kg/h). Low-dose insulin (0.05 units/kg/h) is only started if blood glucose stops falling by 5 mmol/L/h with fluids alone. Prophylactic LMWH is mandatory due to extreme hyperviscosity.
- A. 0.45% (hypotonic) saline is not recommended first-line unless osmolality is not falling despite positive fluid balance, as it can cause rapid intracellular fluid shifts. Immediate insulin is avoided in HHS because it causes a rapid drop in osmolality.
- C. HHS patients have a water deficit of 100-220 ml/kg. Fluid restriction is contraindicated, and aggressive but controlled fluid replacement is the primary therapy.
- D. 5% dextrose is only introduced once the blood glucose falls to 10-15 mmol/L. Giving it initially to a patient with a glucose of 48 mmol/L is incorrect.
Sources: JBDS-IP Guidelines for the Management of Hyperosmolar Hyperglycaemic State
8 / 10
A 22-year-old female with Type 1 diabetes is admitted with a 24-hour history of nausea, vomiting, and abdominal pain. On examination, she is dehydrated, has deep rapid breathing, and a sweet odor on her breath. Labs show: blood glucose 24 mmol/L, arterial pH 7.15, bicarbonates 12 mmol/L, blood ketones 4.2 mmol/L, and potassium 4.8 mmol/L. She is started on IV fluid resuscitation.
Which of the following is the most appropriate initial insulin regimen?
Show answer
Answer: B. Continuous IV insulin infusion at 0.1 units/kg/hour
Why: In the management of DKA, JBDS guidelines recommend a weight-based fixed-rate intravenous insulin infusion (FRIII) at 0.1 units/kg/hour. This is run alongside fluid replacement with 0.9% sodium chloride, and potassium is added to fluids if potassium is between 3.5 and 5.5 mmol/L.
- A. Intravenous insulin is required in DKA due to poor tissue perfusion making subcutaneous absorption unreliable.
- C. Initial bolus insulin is not recommended in DKA as it increases the risk of rapid drops in glucose and potassium, increasing cerebral oedema risk.
- D. Insulin should only be held or delayed if potassium is below 3.5 mmol/L, as insulin shifts potassium intracellularly.
Sources: JBDS Guidelines; NICE NG17
9 / 10
A 28-year-old woman is diagnosed with Graves' disease. The endocrinologist initiates antithyroid therapy with Carbimazole 20mg daily.
What is a rare but life-threatening side effect of Carbimazole that she must be warned about, and what action should she take if she develops a sore throat or fever?
Show answer
Answer: D. Agranulocytosis; stop Carbimazole immediately and attend the hospital for an urgent Full Blood Count (FBC)
Why: Carbimazole is the first-line antithyroid drug in the UK. Agranulocytosis is a rare but serious side effect (occurring in 0.03% of patients). Under MHRA guidelines, patients must receive oral and written warnings: if they develop sore throat, fever, mouth ulcers, or other signs of infection, they must stop Carbimazole immediately and have an urgent FBC checked. If neutropenia is confirmed, Carbimazole must be permanently discontinued.
- A. While hepatotoxicity can occur with antithyroid drugs (especially Propylthiouracil), agranulocytosis is the specific acute risk associated with Carbimazole. Continuing the drug during a sore throat is dangerous.
- B. Pulmonary fibrosis is an adverse effect of Amiodarone, not Carbimazole.
- C. While allergic skin rashes are common with Carbimazole, systemic anaphylaxis is rare and does not warrant routine auto-injector prescription.
Sources: MHRA Drug Safety Update: Carbimazole; NICE NG145
10 / 10
A 12-year-old boy has newly diagnosed type 1 diabetes with marked hyperglycaemia and positive islet autoantibodies. His insulin production is profoundly reduced.
Which pancreatic cell process best explains the insulin deficiency?
Show answer
Answer: C. Autoimmune destruction of pancreatic beta cells
Why: Autoimmune destruction of pancreatic beta cells causes the insulin deficiency in type 1 diabetes. The other islet hormone abnormalities do not explain the positive autoantibodies and loss of insulin secretion.
- A. Insulin resistance is not the primary mechanism in autoimmune type 1 diabetes.
- B. Glucagon can affect glucose levels but does not explain loss of insulin producing cells.
- D. Somatostatin deficiency is not the defining cause of type 1 diabetes.
Sources: NICE NG17, Type 1 diabetes in adults; NICE NG18, Diabetes in children and young people
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Exam-style questions written by MedHub for practice. They are not official exam questions.