What is it?
Hyponatremia (low levels of sodium in the blood)
- Serum sodium concentration of less than 135 mEq/L and can occur on its own or due to complication of other medical illnesses.
- The normal serum sodium concentration is 135-145 mEq/L. Joint European guidelines classify hyponatremia in adults according to serum sodium concentration, as follows [1] :
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Mild: 130-134 mmol/L
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Moderate: 125-129 mmol/L
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Profound: < 125 mmol/L
- When one has low levels of sodium, most persons show no symptoms unless low sodium levels are significant (usually < 115 mEq/L) where one has neurological symptoms and/or water in the brain (brain swelling).
- Patients with long term, severe symptomatic hyponatremia, the rate of correction should not exceed 0.5 mEq/L/h, with a total increase not to exceed 8-10 mEq/L in a 24-hour period.
- The sodium concentration must be corrected to a safe range (usually to ≤ 120 mEq/L) rather than to a normal value.
Hyponatremia is classified according to volume status, as follows:
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Hypovolemic hyponatremia: decrease in total body water with greater decrease in total body sodium
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Euvolemic hyponatremia: normal body sodium with increase in total body water
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Hypervolemic hyponatremia: increase in total body sodium with greater increase in total body water
Hyponatremia can be further subclassified according to effective osmolality, as follows:
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Hypotonic hyponatremia
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Isotonic hyponatremia
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Hypertonic hyponatremia
[1][Guideline] Spasovski G, Vanholder R, Allolio B, Annane D, Ball S, Bichet D, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Nephrol Dial Transplant. 2014 Feb 25. [Medline].
Diagnosis Tests
- Serum osmolality is a measure of the concentration of different solutes in plasma and is primarily determined by sodium, glucose, and urea. Normal range is usually 275–295 mmol/kg and is tightly maintained by Anti diuretic hormone, which regulates fluid balance. An increase in serum osmolality results in secretion of ADH, which increases water reabsorption in the kidneys to return serum osmolality to baseline
- Urine osmolality is a measure of urine concentration and whether this is appropriate for the clinical state of the individual. It provides an estimate of Anti diuretic hormone activity. Normal range is usually 300–900 mmol/kg water. If osmolality ≤100 mOsm/kg (dilute urine), ADH is not acting. If osmolality is >100 mOsm/kg (concentrated urine), Anti diuretic hormone is acting. After 12–14 hours’ fluid restriction, urinary osmolality should be >850 mmol/kg water
- Urinary sodium is a measure of the concentration of sodium in a litre of urine. It is useful for the differential diagnosis of hyponatraemia but must be interpreted alongside volume status, and is therefore difficult to interpret in those taking diuretics
- Serum urea is a marker of extracellular fluid volume. A raised urea may suggest dehydration
- Serum creatinine is useful as an assessment of renal impairment as a cause of hyponatraemia.
Do not wait phone an ambulance, this is an Medical Emergency
Disease or conditions causing deficiency
A low salt diet does not contribute to low sodium levels nor does a high salt diet as normally the kidney removes excess salt (though it can retain fluid and lead to high blood pressure). This condition is determined by fluid intake, a poor diet (malnutrition) as well as any factors that influence the hormones in the brain and body and enzymes in the kidney which control the volume of water in the body.
Syndromes
Medication
Illicit drugs
Sign & Symptom of Deficiency
Complications /Information to beware of/General tips:
Medical Emergency Condition
And/or do not wait, phone for an ambulance if have or develop:
This condition can lead to:
Detailed Information
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