Hyponatremia OSCE History Station Checklist

1. Introduction and consent

• Wash hands, introduce yourself, confirm patient identity.
• Explain: “I understand your blood sodium level is low. I’d like to ask questions to identify symptoms and possible causes.”
• Gain consent, ensure comfort and confidentiality.
• Check immediate stability first: Is the patient alert, fitting, vomiting, or severely confused? If yes, seek urgent senior help.

2. Presenting complaint

• What brought you to hospital?
• When did symptoms begin?
• Did they start suddenly, over hours, or gradually over days/weeks?
• Is this the first episode, or have you had low sodium before?
• Do you know your recent sodium results or whether it is falling quickly?

3. Symptoms of hyponatremia

• Nausea or vomiting
• Headache
• Tiredness, lethargy, weakness
• Dizziness or unsteadiness
• Difficulty concentrating, poor memory
• Falls, especially in older people

• New confusion, agitation, drowsiness, reduced consciousness
• Seizure or collapse
• Severe persistent headache
• Difficulty walking/ataxia
• Visual disturbance or focal weakness

4. Assess volume status through history

A. Features suggesting hypovolemia

• Vomiting, diarrhea, excessive sweating, fever
• Poor oral intake or fasting
• Blood loss: melaena, hematemesis, heavy menstrual bleeding
• Polyuria, nocturia, excessive thirst
• Recent burns or drainage from stoma/NG tube
• Postural dizziness, fainting, reduced urine output
• Recent diuretic use, especially thiazides

B. Features suggesting hypervolemia

• Leg, ankle, abdominal, or facial swelling
• Weight gain
• Breathlessness, orthopnea, paroxysmal nocturnal dyspnea
• Reduced exercise tolerance
• Abdominal distension or jaundice
• Frothy urine or reduced urine output

C. Features suggesting euvolemic hyponatremia / SIADH

• No obvious dehydration or edema
• Excess water intake: “How much do you drink in a day?”
• Compulsive drinking, psychiatric illness, dry mouth
• Low-solute diet: “tea and toast” diet, poor protein/salt intake
• Recent pain, nausea, trauma, surgery, or anesthesia
• Recent chest or CNS illness

5. Search for underlying causes

Endocrine

• Hypothyroid symptoms: cold intolerance, weight gain, constipation, dry skin, lethargy.
• Adrenal insufficiency: fatigue, weight loss, postural dizziness, abdominal pain, vomiting, salt craving, skin darkening.
• Ask about steroid use, recent steroid cessation, pituitary disease, or adrenal disease.

Renal, cardiac, and liver disease

• Known kidney disease, dialysis, or reduced urine output
• Heart failure or ischemic heart disease
• Liver disease, hepatitis, alcohol-related liver disease, ascites
• Diabetes and recent marked hyperglycemia

Respiratory, neurological, and malignancy clues

• Cough, breathlessness, fever, weight loss, hemoptysis
• Smoking history, especially heavy smoking
• Headache, seizures, head injury, stroke symptoms, meningitis/encephalitis symptoms
• Unintentional weight loss, night sweats, reduced appetite

6. Drug history - high-yield OSCE section

• Thiazide diuretics: bendroflumethiazide, hydrochlorothiazide, indapamide
• Loop diuretics
• SSRIs/SNRIs and tricyclic antidepressants
• Antiepileptics: carbamazepine, oxcarbazepine, sodium valproate
• Antipsychotics
• Desmopressin
• Opioids
• NSAIDs
• Proton-pump inhibitors
• Chemotherapy, especially vincristine
• Recent IV fluids, bowel preparation, or perioperative hypotonic fluids

7. Social history and exposures

• Alcohol intake, particularly heavy use or recent binge drinking
• Recreational drugs, especially MDMA/ecstasy
• Diet: malnutrition, very low protein or salt intake
• Excessive water drinking
• Recent endurance exercise or heat exposure with high water intake
• Functional status, falls risk, supports at home

8. Past medical and surgical history

• Previous hyponatremia or admissions with confusion/seizures
• Heart, liver, kidney, thyroid, adrenal, lung, CNS, and psychiatric disease
• Cancer history
• Recent operation, especially prostate/uterine surgery, or recent hospitalization
• Recent infections

9. Systems review

• Constitutional: fever, anorexia, weight loss
• Respiratory: cough, hemoptysis, dyspnea
• Cardiovascular: chest pain, edema, orthopnea
• GI: vomiting, diarrhea, abdominal pain, jaundice
• Urinary: polyuria, dysuria, oliguria
• Neurological: confusion, seizure, headache, focal deficit
• Endocrine: thyroid/adrenal symptoms

10. Close the station

• Summarize the key positives and negatives.
• Explain the need for examination and tests: fluid status, neurological examination, glucose, serum osmolality, renal function, urine osmolality, urine sodium, thyroid and cortisol testing.
• Safety-net: severe headache, repeated vomiting, confusion, drowsiness, or seizures need immediate escalation.

One-minute OSCE summary

“This patient has hyponatremia with/without neurological symptoms. I would establish acuity and assess for red flags such as seizure, reduced consciousness, and severe confusion. I would determine volume status by screening for gastrointestinal/renal fluid loss, edema and cardiorespiratory symptoms, and euvolemic causes. I would take a focused drug history, assess water intake and low-solute diet, screen for endocrine, renal, hepatic, cardiac, CNS, pulmonary, and malignant causes, then examine fluid status and request paired serum and urine osmolality and urine sodium.”

Hyponatremia OSCE History-Taking Marking Scheme

Candidate task

You are the junior doctor in the acute medical unit. A patient has been found to have a low serum sodium concentration. Take a focused history to identify the severity, likely cause, and immediate risks of hyponatremia. You do not need to examine the patient or formulate a management plan.

Examiner checklist

Marking detail

1. Introduction and communication: 3 marks

• 1 mark: Introduces self and confirms identity.
• 1 mark: Explains that the history aims to identify why sodium is low and whether it is causing symptoms.
• 1 mark: Gains consent, maintains rapport, and uses patient-centred communication.

2. Immediate safety assessment: 4 marks

• Seizure, collapse, or loss of consciousness.
• Confusion, agitation, drowsiness, or reduced conscious level.
• Severe headache, persistent vomiting, marked weakness, or gait disturbance.
• Clarifies timing: acute onset over hours versus gradual onset over days/weeks.

3. Presenting complaint and symptoms: 3 marks

• 1 mark: Establishes the presenting complaint and chronology.
• 1 mark: Asks about nausea, vomiting, headache, fatigue, and weakness.
• 1 mark: Asks about cognitive and neurological symptoms, including falls, confusion, and poor concentration.

4. Hypovolemic cause screen: 3 marks

• 1 mark: Gastrointestinal loss: vomiting, diarrhea, stoma/NG losses.
• 1 mark: Reduced intake or excess loss: poor intake, sweating, fever, burns.
• 1 mark: Renal loss or dehydration features: diuretics, polyuria, thirst, postural dizziness, oliguria.

5. Hypervolemic cause screen: 3 marks

• 1 mark: Peripheral edema or weight gain.
• 1 mark: Heart failure symptoms: breathlessness, orthopnea, PND.
• 1 mark: Liver/renal disease features: ascites, jaundice, frothy urine, oliguria.

6. Euvolemic causes and fluid intake: 3 marks

• 1 mark: Quantifies daily fluid intake and asks about excessive water consumption.
• 1 mark: Screens for primary polydipsia, psychiatric illness, or compulsive drinking.
• 1 mark: Screens for low dietary solute intake, recent surgery, pain, nausea, or hypotonic IV fluids.

7. Drug history: 4 marks

• 1 mark: Asks about medication changes and non-prescription drugs.
• 1 mark: Diuretics, especially thiazides.
• 1 mark: SSRIs, tricyclics, antipsychotics, carbamazepine/oxcarbazepine.
• 1 mark: Desmopressin, opioids, NSAIDs, chemotherapy, or recent IV fluids.

8. Relevant past medical history: 3 marks

• 1 mark: Renal, cardiac, or liver disease.
• 1 mark: Thyroid disease, adrenal insufficiency, steroid use or recent steroid withdrawal.
• 1 mark: Pulmonary/CNS disease, infection, or malignancy. Consider SIADH clues such as chronic cough, weight loss, or heavy smoking.

9. Social history and exposures: 2 marks

• 1 mark: Alcohol intake, nutrition, and recent dietary restriction.
• 1 mark: MDMA/recreational drug use, smoking, prolonged exercise, and excessive water intake.

10. Close and summary: 2 marks

• 1 mark: Gives a structured summary identifying likely volume status and possible causes.
• 1 mark: States next steps: examination, medication review, fluid balance, serum osmolality, glucose, renal function, urine osmolality, urine sodium, thyroid function, and morning cortisol as indicated.

Global rating scale

Examiner prompts if candidate stalls

• “Is there anything else you would like to ask about their fluid intake?”
• “Would you like to ask about medications?”
• “Any relevant past medical conditions?”
• “Is there anything you would ask to assess urgency?”

Key examiner facts

• Symptoms may range from nausea, lethargy, headache, and unsteadiness to confusion, seizures, and reduced consciousness.
• A rapid fall in sodium can cause serious neurological symptoms even when the absolute sodium value is not extremely low.
• History should help classify the patient as hypovolemic, euvolemic, or hypervolemic.
• Drug history is especially important in hyponatremia.
  Harrison’s Principles of Internal Medicine, 22e, p. 393.
• Volume status assessment is central to diagnosis.
  The Washington Manual of Medical Therapeutics, Diagnostic Testing, pp. 2427-2436.