Sodium 132 mmol/L — mild hyponatraemia and what drives it
Serum sodium of 132 mmol/L is mild hyponatraemia (reference range typically 135-145 mmol/L). Sodium is the dominant determinant of plasma osmolality, and persistent hyponatraemia means the body has more water than sodium — either from overall water excess (over-hydration / SIADH), sodium loss (diuretic effects, GI losses, adrenal insufficiency), or ineffective volume status (heart failure, cirrhosis). Mild chronic hyponatraemia is often asymptomatic but is associated in cohort studies with falls, attention problems, and bone-density loss; severe acute hyponatraemia is a medical emergency. Clinical workup distinguishes the cause by assessing volume status and urine sodium.
Reference ranges
| Standard reference | 135 – 145 mmol/L |
| Mild hyponatraemia | 130 – 134 mmol/L |
| Moderate | 125 – 129 mmol/L |
| Severe (medical emergency) | < 120 mmol/L |
What this marker measures
Serum sodium reflects the relative concentration of sodium ions in plasma. Hyponatraemia is almost never a 'sodium deficiency' — total body sodium is usually fine — it's a relative water excess. The body tightly regulates plasma osmolality (which sodium drives) via vasopressin (ADH) and thirst; chronic mild hyponatraemia indicates a regulatory disturbance.
Why might it be low?
- ·Over-hydration (excessive water intake, especially endurance athletes)
- ·Thiazide diuretic use
- ·SSRI / SNRI antidepressants (SIADH)
- ·Heart failure (effective volume depletion → ADH activation)
- ·Cirrhosis (similar mechanism)
- ·Hypothyroidism
- ·Adrenal insufficiency
- ·SIADH from pulmonary or CNS pathology
- ·Chronic pain or nausea (ADH stimulation)
Why might it be elevated?
- ·Dehydration (water deficit > sodium deficit)
- ·Diabetes insipidus (rare, severe)
- ·Excessive sodium intake (uncommon — kidneys excrete it)
FAQ
Should I add salt to my diet?+
Almost never the right answer for hyponatraemia. The problem is usually water excess or hormonal regulation, not dietary sodium deficiency. The clinical workup — checking volume status, urine sodium, urine osmolality — guides actual treatment. This is not a self-management area.
How quickly can it be corrected?+
Critical caveat: rapid correction of chronic hyponatraemia can cause central pontine myelinolysis (osmotic demyelination), a severe neurological complication. Correction in chronic cases is deliberately slow (≤8-12 mmol/L per 24 hours). This is strictly clinical management — not for self-administration adjustment.
This page describes biomarker research and reference ranges for self-tracking and research-context discussion only. It is not medical advice, not a diagnosis, and not a substitute for a qualified physician. Take any concerns about your health to a clinician.
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