Blood results interpretation — hyponatraemia and the management plan

PLAB 2 & PRES 3 · nephrology / data interpretation · medium · 10 minutes

Candidate brief

You are an FY2 doctor in a GP surgery. Mrs Irene Kowalski, 78, is attending for review of blood results taken yesterday. Her blood pressure had been creeping up, and indapamide 1.5 mg daily was started three weeks ago. These are her results (previous values from two months ago in brackets): Sodium 118 mmol/L (138) Potassium 3.3 mmol/L (4.1) Urea 8.9 mmol/L (6.2) Creatinine 92 micromol/L (84), eGFR 58 Glucose 5.8 mmol/L, adjusted calcium 2.32 mmol/L, LFTs normal, FBC normal She feels "a bit sick and wobbly" but wanted to keep the appointment. Her observations are stable. Please interpret the results, assess the patient, explain your findings, and set out your management plan.

What examiners look for

Hyponatraemia is graded by number AND symptoms, and the two do not always travel together. 118 mmol/L is profound on paper; nausea and unsteadiness make it symptomatic in person. The combination — not either alone — is what sends her to hospital today. The drug chart is the first investigation. A sodium that was 138 before a thiazide-like diuretic and 118 three weeks after it has told you its cause with a timestamp. Indapamide, SSRIs and PPIs fill the hyponatraemia league table; the timeline is the diagnostic test candidates forget to run. Volume status decides the physiology: euvolaemic rules out simple dehydration, points toward drugs/SIADH, and kills the reflex "give fluids" answer. Lying and standing BP, JVP and oedema take ninety seconds and redirect the entire plan. Slow is safe. Chronic hyponatraemia corrected faster than roughly 10 mmol/L in 24 hours risks osmotic demyelination — a devastating, preventable injury caused by the treatment, not the disease. "Just give salt and recheck next week" fails at both ends: too slow for a symptomatic 118 today, and unsupervised correction can overshoot tomorrow. In primary care, your job is recognition, disposition and not making it worse: stop the culprit diuretic, restrict (never push) fluids, phone the medical team, tell the family, and write the handover. The elegant part of this station is a GP decision made on time — not a fluid chart. And handle the person: she is frightened of hospitals for a reason with a name and a funeral in it. Explaining WHY today, WHY monitored, and WHY slow gets her on the ambulance willingly — which is also, not coincidentally, the safest outcome.

Guideline references

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