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.

Urine Test

Fractional Excretion of Urea

2.6

0.6

FEUrea > 50%

Differential Diagnosis: Hypovolemia

Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618

Untagged

Finding	+LR	-LR	Comments, Study
Clinical Assessment of Volume Status	1	1	Study: Am J Med. 1987 Nov;83(5):905-8. PMID: 3674097
Fractional Excretion of Sodium	inf	0.3	FENa > 0.5% Differential Diagnosis: Hypovolemia 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) Differential Diagnosis: Hypovolemia 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) Differential Diagnosis: Hypovolemia 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. Differential Diagnosis: Hypovolemia Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618