Syndrome of Inappropriate ADH Secretion: Sensitivity and Specificity

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 sensitivity and specificity of findings for Syndrome of Inappropriate ADH Secretion are listed below. See the left navigation bar to change the display.

Specific Findings

Fractional Excretion of Sodium

68%

100%

FENa > 0.5%

Differential Diagnosis: Hypovolemia

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

Sensitive Findings

Urine Sodium

90%

70%

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

Poorly Diagnostic Findings

Finding	Sensitivity	Specificity	Comments, Study
Plasma Urea	80%	80%	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
Fractional Excretion of Urea	52%	80%	FEUrea > 50% Differential Diagnosis: Hypovolemia Study: Clin J Am Soc Nephrol. 2008 Jul;3(4):1175-84. PMID: 18434618
Uric Acid	73%	59%	uric acid < 4mg/dl suggests SIADH (because of dilution) Differential Diagnosis: Hypovolemia Study: Int Urol Nephrol. 2001;32(3):475-93. PMID: 11583374
Clinical Assessment of Volume Status	48%	53%	Study: Am J Med. 1987 Nov;83(5):905-8. PMID: 3674097