Hyponatremia: Difference between revisions
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* Serum Na <134? |
* Serum Na <134? |
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* Measure serum osmolality and urea level |
* Measure serum osmolality and urea level |
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| − | ** Sosm |
+ | ** Sosm ≥ 280: normotonic/hypertonic |
*** Ddx includes pseudohyponatremia (from hyperlipidemia, hyperparaproteinemia, etc.), or presence of osmotically active substances (glucose, mannitol) |
*** Ddx includes pseudohyponatremia (from hyperlipidemia, hyperparaproteinemia, etc.), or presence of osmotically active substances (glucose, mannitol) |
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** Sosm <280 mOsm/kg: true hyponatremia |
** Sosm <280 mOsm/kg: true hyponatremia |
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*** Uosm <100 mOsm/kg: normal water excretion |
*** Uosm <100 mOsm/kg: normal water excretion |
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**** Primary polydipsiea or reset osmostat syndrome |
**** Primary polydipsiea or reset osmostat syndrome |
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| − | *** Uosm |
+ | *** Uosm ≥ 100 mOsm/kg: impaired water excretion |
**** Exclude hypothyroidism and adrenal insufficiency with morning cortisol and TSH |
**** Exclude hypothyroidism and adrenal insufficiency with morning cortisol and TSH |
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**** Measure urine sodium |
**** Measure urine sodium |
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**** UNa between 20 and 40 mmol/L |
**** UNa between 20 and 40 mmol/L |
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***** Bolus 2L/day normal saline for 2 days and trend sodium |
***** Bolus 2L/day normal saline for 2 days and trend sodium |
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| − | ***** If SNa increases by |
+ | ***** If SNa increases by ≥ 5 mmol/L: hypovolemia |
***** If SNa increases by <5 mmol/L: SIADH or reset ostmostat |
***** If SNa increases by <5 mmol/L: SIADH or reset ostmostat |
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****** FEurea >55%, serum urate <0.24, and FEurate >10%: SIADH |
****** FEurea >55%, serum urate <0.24, and FEurate >10%: SIADH |
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Revision as of 11:31, 30 September 2022
Differential Diagnosis
- Pseudohyponatremia from lab error
- Translational hyponatremia from mannitol or hyperglycemia
- Hypovolemic
- UNa >20: Renal losses, including mineralocorticoid deficiency
- UNa <10: Non-renal losses
- Euvolemic
- Uosm >100: SIADH, hypothyroidism, glucocorticoid deficiency
- Uosm <100: Primary polydipsia, low solute intake
- Uosm variable: Reset osmostat
- Hypervolemic
- UNa <10: CHD, cirrhosis, nephrosis
- UNa >20: Renal failure
Investigations
- Serum and urine osmolality and electrolytes (prior to treatment)
- TSH and AM cortisol
Diagnosis by Lab Criteria
- Serum Na <134?
- Measure serum osmolality and urea level
- Sosm ≥ 280: normotonic/hypertonic
- Ddx includes pseudohyponatremia (from hyperlipidemia, hyperparaproteinemia, etc.), or presence of osmotically active substances (glucose, mannitol)
- Sosm <280 mOsm/kg: true hyponatremia
- Measure urine osmolality
- Uosm <100 mOsm/kg: normal water excretion
- Primary polydipsiea or reset osmostat syndrome
- Uosm ≥ 100 mOsm/kg: impaired water excretion
- Exclude hypothyroidism and adrenal insufficiency with morning cortisol and TSH
- Measure urine sodium
- UNa < 20 mmol/L: hypovolemia, including EABV depletion (heart failure, cirrhosis, nephrotic syndrome)
- UNa > 40 mmol/L: SIADH, reset ostmostat, renal salt wasting
- Salt supplementation and water restriction
- Normal serum urate and reduced FEurate: SIADH
- Hypouricemia and unchanged FEurate: renal salt wasting
- UNa between 20 and 40 mmol/L
- Bolus 2L/day normal saline for 2 days and trend sodium
- If SNa increases by ≥ 5 mmol/L: hypovolemia
- If SNa increases by <5 mmol/L: SIADH or reset ostmostat
- FEurea >55%, serum urate <0.24, and FEurate >10%: SIADH
- Oral or IV water-loading test: reset osmostat syndrome
- Sosm ≥ 280: normotonic/hypertonic
Further Reading
- Milionis HJ, Liamis GL, and Elisaf MS. The hyponatremic patient: a systematic approach to laboratory diagnosis. CMAJ. 2002;166(8):1056-1062.
