Refeeding Syndrome — MRCPsych Paper B MCQ

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HardEating DisordersRefeeding SyndromeMRCPsych Paper B

A 19-year-old woman with anorexia nervosa has a BMI of 12.8 kg/m² and has had negligible nutritional intake for 10 days. Forty-eight hours after supervised refeeding begins, she develops tachypnoea and marked generalised weakness. The suspected electrolyte shift would impair ATP production and reduce erythrocyte 2,3-diphosphoglycerate. Which serum electrolyte is the most important early biochemical indicator of refeeding syndrome in this case?

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Correct answer: C — Phosphate

The correct answer is C, phosphate. Refeeding increases insulin secretion, driving phosphate into cells for phosphorylation reactions. The resulting hypophosphataemia reduces ATP and erythrocyte 2,3-diphosphoglycerate, potentially causing muscle weakness, respiratory failure, neurological dysfunction and cardiac compromise. RCPsych MEED guidance identifies hypophosphataemia as an important early indicator heralding refeeding syndrome. Potassium and magnesium may also fall during refeeding and can cause arrhythmias or neuromuscular abnormalities, but they do not best explain the ATP and 2,3-diphosphoglycerate findings. Sodium and water retention may cause oedema, while hypocalcaemia can occur secondarily, particularly with magnesium deficiency, but neither is the characteristic early biochemical indicator.

Reference: Royal College of Psychiatrists. CR233: Medical Emergencies in Eating Disorders — Guidance on Recognition and Management, section 4b, 2022. https://www.rcpsych.ac.uk/docs/default-source/improving-care/better-mh-policy/college-reports/college-report-cr233-medical-emergencies-in-eating-disorders-%28meed%29-guidance.pdf?sfvrsn=2d327483_55