Lab Tests Online
133 – 146 mmol/L
How should I investigate a patient with low serum sodium?
Answer: We recommend:
- Establish history of fluid intake and current treatments
- Assess fluid status, to identify whether hypovolaemia or hypervolaemia is present
- Repeat to confirm and establish whether acute and changing or chronic and stable. Changes of up to 5 mmol/L can reflect non-significant variation
Depending on result:
- Persistent and stable serum Na 132-135 mmol/L in a clinically well patient may reflect a statistical population outlier and may not require investigation unless large recent fall
- Serum Na 125-131 mmol/L
- Check serum potassium, urea, creatinine and plasma glucose.
- If cause not clinically apparent check
- Urine Na and osmolality if SIADH suspected
- If Urine Na > 30 mmol/ L and urine osmolality significantly higher than serum osmolality this suggests SIADH
- Consider Addison’s disease and hypothyroidism
- Consider effects of drug therapy
- Consider reset osmostat syndrome in patients with chronic illness and stable hyponatraemia
- Consider artefactual causes: Hyperproteinaemia (eg myeloma) or severe hyperlipidaemia
- Serum Na 115-124 mmol/L
- Check as above
- Seek specialist advice unless long term stable and cause established
- Consider immediate admission if Na falling rapidly or neurological signs or symptoms present
- Serum Na <115 mmol/L
- Immediate admission usually indicated
How should I investigate a patient with raised serum sodium?
Answer: Hypernatraemia can be defined as a serum sodium > 145 mmol/L
- Repeat to confirm and establish whether acute and changing or chronic and stable. Changes of up to 5 mmol/L can reflect non significant variation
- Establish history of thirst, fluid intake and losses and current treatments
- Check for clinical features of dehydration and/or hypovolaemia
Depending on result:
Persistent serum Na 146-148 mmol/L without clinical features of hypovolaemia may reflect a statistical population outlier.
Serum Na 149 – 154 mmol/L
- Request serum potassium, urea, creatinine, calcium, and plasma glucose to evaluate further hydration status and renal function and exclude diabetes mellitus and hypercalcaemia as causes for dehydration
- Request serum lithium in patients treated with lithium
- Request urine and serum osmolality if diabetes insipidus suspected (In DI high serum osmolality (>300 mOsm/Kg) and inappropriately dilute urine (less than serum)
- Consider specialist advice if clinical cause not apparent or oral rehydration is indicated but is not realistically practical.
Serum Na > 155 mmol/L
- Seek specialist advice or admission in addition to above
Turn around Time
Can be added on to an existing request up to 4 days following sample receipt
Specimen Labelling Procedure