Hyponatremia: Difference between revisions

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== Differential Diagnosis ==
== Etiologies ==


* Medications: [[thiazide]] and thiazide-type diuretics, [[mannitol]], [[IVIG]], [[desmopressin]] (dDAVP), [[ecstasy]] (methylenedioxymethamphetamine), and some antidepressants, antiepileptics, and antipsychotics
* [[Pseudohyponatremia]] from lab error
* [[Translational hyponatremia]] from [[mannitol]] or [[hyperglycemia]]
* Hypovolemic
** U<sub>Na</sub> &gt;20: Renal losses, including [[mineralocorticoid deficiency]]
** U<sub>Na</sub> &lt;10: Non-renal losses
* Euvolemic
** U<sub>osm</sub> &gt;100: [[SIADH]], [[hypothyroidism]], [[glucocorticoid deficiency]]
** U<sub>osm</sub> &lt;100: [[Primary polydipsia]], low solute intake
** U<sub>osm</sub> variable: Reset osmostat
* Hypervolemic
** U<sub>Na</sub> &lt;10: CHD, [[cirrhosis]], [[nephrosis]]
** U<sub>Na</sub> &gt;20: [[Renal failure]]


==Differential Diagnosis==
== Investigations ==


*[[Pseudohyponatremia]] from lab error
* Serum and urine osmolality and electrolytes (prior to treatment)
*[[Translational hyponatremia]] from [[mannitol]] or [[hyperglycemia]]
* TSH and AM cortisol
*Hypovolemic
**U<sub>Na</sub> &gt;20: Renal losses, including [[mineralocorticoid deficiency]]
**U<sub>Na</sub> &lt;10: Non-renal losses
*Euvolemic
**U<sub>osm</sub> &gt;100: [[SIADH]], [[hypothyroidism]], [[glucocorticoid deficiency]]
**U<sub>osm</sub> &lt;100: [[Primary polydipsia]], low solute intake
**U<sub>osm</sub> variable: Reset osmostat
*Hypervolemic
**U<sub>Na</sub> &lt;10: CHD, [[cirrhosis]], [[nephrosis]]
**U<sub>Na</sub> &gt;20: [[Renal failure]]


==Investigations==
== Further Reading ==


*Serum and urine osmolality and electrolytes (prior to treatment)
* Milionis HJ, Liamis GL, and Elisaf MS. [https://www.cmaj.ca/content/166/8/1056 The hyponatremic patient: a systematic approach to laboratory diagnosis]. ''CMAJ''. 2002;166(8):1056-1062.
*[[TSH]] and AM cortisol

=== Diagnosis by Lab Criteria ===

* Serum Na (S<sub>Na</sub>) <134?
* Measure serum osmolality (S<sub>osm</sub>) and urea level (S<sub>urea</sub>)
** S<sub>osm</sub> ≥ 280: normotonic/hypertonic
*** Differential includes [[pseudohyponatremia]] (from [[hyperlipidemia]], [[hyperparaproteinemia]], etc.), or presence of osmotically active substances ([[glucose]], [[mannitol]])
** S<sub>osm</sub> <280 mOsm/kg: true hyponatremia
*** Measure urine osmolality (U<sub>osm</sub>)
*** U<sub>osm</sub> <100 mOsm/kg: normal water excretion
**** [[Primary polydipsia]] or [[reset osmostat syndrome]]
*** U<sub>osm</sub> ≥ 100 mOsm/kg: impaired water excretion
**** Exclude [[hypothyroidism]] and [[adrenal insufficiency]] with morning cortisol and TSH
**** Measure urine sodium (U<sub>Na</sub>)
**** U<sub>Na</sub> < 20 mmol/L: [[hypovolemia]], including EABV depletion ([[heart failure]], [[cirrhosis]], [[nephrotic syndrome]])
**** U<sub>Na</sub> > 40 mmol/L: [[SIADH]], [[Reset osmostat syndrome|reset osmostat]], renal salt wasting
***** Salt supplementation and water restriction
***** Normal S<sub>urate</sub> and reduced FE<sub>urate</sub>: SIADH
***** Hypouricemia and unchanged FE<sub>urate</sub>: renal salt wasting
**** U<sub>Na</sub> between 20 and 40 mmol/L
***** Bolus 2L/day normal saline for 2 days and trend sodium
***** If S<sub>Na</sub> increases by ≥ 5 mmol/L: hypovolemia
***** If S<sub>Na</sub> increases by <5 mmol/L: [[SIADH]] or [[Reset osmostat syndrome|reset osmostat]]
****** FE<sub>urea</sub> >55%, S<sub>urate</sub> <0.24, and FE<sub>urate</sub> >10%: SIADH
****** Oral or IV water-loading test: [[Reset osmostat syndrome|reset osmostat]]

== Management ==

* Depends on cause
* Goal rate of correction in chronic hyponatremia should be 4 to 6 mEq/L in 24 hours (max of 8 mEq) in order to reduce the risk of [[osmotic demyelination syndrome]]

==Further Reading==

*Milionis HJ, Liamis GL, and Elisaf MS. [https://www.cmaj.ca/content/166/8/1056 The hyponatremic patient: a systematic approach to laboratory diagnosis]. ''CMAJ''. 2002;166(8):1056-1062.


[[Category:Nephrology]]
[[Category:Nephrology]]

Latest revision as of 20:05, 9 March 2024

Etiologies

Differential Diagnosis

Investigations

  • Serum and urine osmolality and electrolytes (prior to treatment)
  • TSH and AM cortisol

Diagnosis by Lab Criteria

Management

  • Depends on cause
  • Goal rate of correction in chronic hyponatremia should be 4 to 6 mEq/L in 24 hours (max of 8 mEq) in order to reduce the risk of osmotic demyelination syndrome

Further Reading