How can I differentiate between hypernatraemia due to dehydration and that due to excess sodium intake?

To differentiate hypernatraemia caused by dehydration from that caused by excess sodium intake, assess the patient's volume status and clinical signs:

• Hypernatraemia due to dehydration typically presents with signs of hypovolaemia such as dry mucous membranes, decreased skin turgor, sunken eyes, tachycardia, and reduced urine output. There may also be neurological symptoms like jittery movements, increased muscle tone, hyperreflexia, convulsions, drowsiness, or coma in severe cases. These signs reflect water loss exceeding sodium loss, leading to hypernatraemic dehydration ².
• Hypernatraemia due to excess sodium intake usually presents with hypervolaemia or euvolaemia, without the clinical signs of dehydration. The patient may have a history of excessive sodium ingestion or iatrogenic sodium administration. Volume status assessment is key, as these patients do not show hypovolaemic signs but may have hypertension or oedema.
• Laboratory investigations can support differentiation: in dehydration, there is often elevated urea and creatinine due to volume depletion, whereas in sodium excess, these may be normal or reflect volume overload. Urine sodium and osmolality measurements can help assess renal handling of sodium and water ³.
• Management differs accordingly: dehydration requires careful fluid replacement with isotonic saline initially, monitoring plasma sodium to avoid rapid correction, while sodium excess may require fluid restriction and addressing the sodium load ²,³.