Hyponatremia
Low sodium does not automatically mean sodium deficit.
A Sodium Value Is Not the Diagnosis
Serum sodium reflects the relationship between body water and exchangeable solute.
Interpretation starts with acuity, symptoms, tonicity, glucose, volume context and medications.
Symptoms and Acuity Drive Urgency
A stable chronic sodium and a rapid fall to the same number are not equivalent.
Headache, vomiting, confusion, marked somnolence or seizure raises concern for acute symptomatic hypotonic hyponatremia requiring urgent treatment.
Classify the Context
Think hypovolemic, euvolemic or hypervolemic. Review thiazides, SSRIs/SNRIs, anticonvulsants and desmopressin.
When needed, serum/urine osmolality and urine sodium help clarify the mechanism. Pseudohyponatremia — a lab artifact from marked hyperlipidemia or hyperproteinemia — shows normal plasma osmolality and requires no treatment.
Don't Reflexively 'Give Salt'
Heart failure and cirrhosis can produce hyponatremia despite total-body sodium excess.
Hyperglycemia can also lower measured sodium without classic hypotonic hyponatremia.
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