Syndrome of Inappropriate ADH Secretion: Likelihood Ratios

Introduction: SIADH a major cause of hyponatremia and represents the condition when a euvolemic patient has increased ADH causing inappropriate retention of free water. The diagnosis is important as the treatment is fluid restriction rather than normal saline infusion.

For a review of the diagnosis, see http://cjasn.asnjournals.org/cgi/content/full/3/4/1175 (PMID 18434618)

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Differential Diagnoses include: Hypovolemia

Prevalence

Population / Calculator	Prevalence	Comments / Study / Link
Elderly patients with hyponatremia	31%	110 consecutive cases: 31% SIADH patients, 23% patients with hyponatremia due to diuretics, 18% potomania patients, 15% salt depleted patients, 5% salt depleted SIADH patients, 5% patients with a salt loosing syndrome and 3% patients with hyponatremia of unknown origin Int Urol Nephrol. 2001;32(3):475-93. PMID: 11583374
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The likelihood ratios of findings for Syndrome of Inappropriate ADH Secretion are listed below. See the left navigation bar to change the display.

Hypovolemia

Finding	+LR	-LR	Comments, Study
Fractional Excretion of Sodium	inf	0.3	FENa > 0.5% Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618
Fractional Excretion of Urea	2.6	0.6	FEUrea > 50% Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618
Plasma Urea	4	0.3	plasma Urea < 30 mg/dl suggests SIADH (because of dilution) Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618
Uric Acid	1.8	0.5	uric acid < 4mg/dl suggests SIADH (because of dilution) Study: Int Urol Nephrol. 2001;32(3):475-93. PMID: 11583374
Urine Sodium	3	0.1	UNa > 30 indicates SIADH. However, UNa can be high in hypovolemic patients, especially those with low UOP. Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618

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Clinical Assessment of Volume Status

Study: Am J Med. 1987 Nov;83(5):905-8. PMID: 3674097