Sodium (Serum): What Your Result Means

What is Sodium (Serum)?

Sodium (135–145 mmol/L typically) is the principal extracellular cation, and serum concentration essentially reports osmolality — how dilute or concentrated your blood runs. Kidneys, ADH (vasopressin), and thirst jointly defend it within millimolar precision.

Typical reference interval: Approximately 135–145 mmol/L.. Laboratories differ — the interval printed on YOUR report always governs.

If your Sodium (Serum) is high

Common reasons Sodium (Serum) runs above the reference interval:

• Dehydration/water deprivation — hypernatremia = water deficit until proven otherwise
• Diabetes insipidus — ADH missing or ignored — massive dilute urine output
• Osmotic diuresis — uncontrolled glucosuria drags water out
• Iatrogenic — hypertonic saline, sodium bicarbonate loads

If your Sodium (Serum) is low

Common reasons Sodium (Serum) runs below the reference interval:

• Diuretics — especially thiazides — the outpatient champion of hyponatremia
• SIADH — inappropriate ADH from lung lesions, medications (SSRIs, carbamazepine), nausea, pain
• Heart failure, cirrhosis — low effective volume triggers water retention disproportionate to sodium
• Psychogenic polydipsia — drinking beyond renal clearing capacity
• Pseudohyponatremia — severe hyperlipidemia/protein states distort measurement — osmolality clarifies
• Exercise-associated — over-hydration during endurance events — historically fatal marathon myth 'drink maximum water'

Symptoms worth knowing

Brain cells swell or shrink with water shifts, so symptoms run neurologic: hyponatremia brings headache, nausea, confusion, gait instability, seizures as it deepens; hypernatremia brings thirst, agitation, lethargy. Speed of onset determines danger more than depth — chronic 118 survives intact, acute 122 can herniate.

What usually happens next

1. Never correct rapidly either direction — osmotic demyelination (central pontine myelinolysis) is the feared iatrogenic disaster
2. Serum osmolality and urine osmolality/sodium triple clarify most confusing cases
3. Review thiazide use first in outpatients — it's that common

Frequently asked questions about Sodium (Serum) results