eMedicine Specialties > Emergency Medicine > Endocrine & Metabolic

Syndrome of Inappropriate Antidiuretic Hormone Secretion: Differential Diagnoses & Workup

Author: Keenan Bora, MD, Fellow, Medical Toxicology, Detroit Medical Center; Attending Physician, Medical Center Emergency Services, Detroit
Coauthor(s): Meher Chaudhry, MD, Chief Resident, Department of Emergency Medicine, Detroit Receiving Hospital, University Health Center
Contributor Information and Disclosures

Updated: Oct 20, 2009

Differential Diagnoses

Adrenal Insufficiency and Adrenal Crisis
Malnutrition
Cerebral salt wasting
Pediatrics, Diabetic Ketoacidosis
Diabetic Ketoacidosis
Pregnancy
Hyperglycemia
Pseudohyponatremia (hyperlipidemia, hyperproteinemia)
Hyperprolactinemia
Psychogenic polydipsia
Hyponatremia
Waldenstrom Hypergammaglobulinemia
Hypopituitarism
Hypothyroidism and Myxedema Coma

Other Problems to Be Considered

CHF
Liver cirrhosis
Nephrotic syndrome
Hypothyroidism
Addison disease
Hypopituitarism
Primary polydipsia
Compulsive water drinking

Workup

Laboratory Studies

  • Serum: Electrolytes, BUN, creatinine, glucose levels, and osmolality
    • Hyponatremia (sodium <135 mEq/L): Serum potassium and bicarbonate levels are normal in SIADH. Hypokalemia and metabolic alkalosis suggest diuretic therapy or vomiting.
    • BUN and serum uric acid levels tend to fall because of plasma dilution and increased excretion of nitrogenous products.
    • Low serum osmolality (<280 mOsm/kg)
    • Hyperkalemia and metabolic acidosis coexisting with hyponatremia suggest adrenal insufficiency.
    • Elevated glucose levels decrease the measured serum sodium levels by 1.6 mEq/L for every 100 mg/dL increase in glucose. This results from the osmotic effect of glucose drawing water into the intravascular space. The serum sodium level rises as hyperglycemia is corrected.
  • Urine: Electrolytes and osmolality (specific gravity is nonspecific but sensitive)
    • Elevated urinary sodium level (>20 mmol/L). It would be preferable to check urine electrolytes at the same time as the serum electrolytes to determine the fractional excretion of sodium or FeNa.
    • Urine osmolality generally >100 mOsm/L
  • Plasma cortisol level may be obtained to exclude adrenal insufficiency.
  • Pseudohyponatremia occurs with severe hyperlipidemia and with hyperproteinemia (levels >10 g/dL, as seen in multiple myeloma).

Imaging Studies

  • Chest radiographs may reveal an underlying cause (eg, pulmonary disease, lung carcinoma).
  • CT scan of the head may be appropriate in selected cases.

    • CT scan may show evidence of cerebral edema (eg, narrowing of the ventricles) or may identify a CNS disorder responsible for SIADH (eg, brain tumor).
    • CT helps rule out other potential causes of acute changes in neurologic status.

Other Tests

  • Serum ADH levels tend to not be available on a stat basis.
  • Isolated hyponatremia has no consistent effect on ECG.

More on Syndrome of Inappropriate Antidiuretic Hormone Secretion

Overview: Syndrome of Inappropriate Antidiuretic Hormone Secretion
Differential Diagnoses & Workup: Syndrome of Inappropriate Antidiuretic Hormone Secretion
Treatment & Medication: Syndrome of Inappropriate Antidiuretic Hormone Secretion
Follow-up: Syndrome of Inappropriate Antidiuretic Hormone Secretion
References
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References

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  2. Verbalis JG, Berl T. Disorders of water balance. In: Brenner BM. Brenner & Rector's The Kidney. Vol 1. 8th ed. Saunders; 2007:459-491.

  3. Leaf A, Mamby AR. An antidiuretic mechanism not regulated by extracellular fluid tonicity. J Clin Invest. Jan 1952;31(1):60-71. [Medline].

  4. Rai A, Whaley-Connell A, McFarlane S, Sowers JR. Hyponatremia, arginine vasopressin dysregulation, and vasopressin receptor antagonism. Am J Nephrol. 2006;26(6):579-89. [Medline].

  5. Decker BC. Disorders of Water Excess: Hyponatremia. In: Dale DC, Federman DD, eds. ACP Medicine. Vol 1. BC Decker; 2007.

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  8. Stelfox HT, Ahmed SB, Khandwala F, Zygun D, Shahpori R, Laupland K. The epidemiology of intensive care unit-acquired hyponatraemia and hypernatraemia in medical-surgical intensive care units. Crit Care. 2008;12(6):R162. [Medline].

  9. Hsu YJ, Chiu JS, Lu KC, Chau T, Lin SH. Biochemical and etiological characteristics of acute hyponatremia in the emergency department. J Emerg Med. Nov 2005;29(4):369-74. [Medline].

  10. Renneboog B, Musch W, Vandemergel X, Manto MU, Decaux G. Mild chronic hyponatremia is associated with falls, unsteadiness, and attention deficits. Am J Med. Jan 2006;119(1):71.e1-8. [Medline].

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  17. Mohmand HK, Issa D, Ahmad Z, Cappuccio JD, Kouides RW, Sterns RH. Hypertonic saline for hyponatremia: risk of inadvertent overcorrection. Clin J Am Soc Nephrol. Nov 2007;2(6):1110-7. [Medline].

  18. [Best Evidence] Schrier RW, Gross P, Gheorghiade M, Berl T, Verbalis JG, Czerwiec FS. Tolvaptan, a selective oral vasopressin V2-receptor antagonist, for hyponatremia. N Engl J Med. Nov 16 2006;355(20):2099-112. [Medline].

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Further Reading

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Keywords

SIADH, antidiuretic hormone, ADH, vasopressin, syndrome of inappropriate antidiuretic hormone secretion, hyponatremia, elevated urine osmolality, excessive sodium excretion, renal excretion of water, concentrated urine, ADH dysregulation, exercise-induced hyponatremia, osmolarity, cerebral salt wasting, reset osmostat

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Contributor Information and Disclosures

Author

Keenan Bora, MD, Fellow, Medical Toxicology, Detroit Medical Center; Attending Physician, Medical Center Emergency Services, Detroit
Keenan Bora, MD is a member of the following medical societies: American Academy of Clinical Toxicology, American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Medical Toxicology, and American Medical Association
Disclosure: Nothing to disclose.

Coauthor(s)

Meher Chaudhry, MD, Chief Resident, Department of Emergency Medicine, Detroit Receiving Hospital, University Health Center
Disclosure: Nothing to disclose.

Medical Editor

Erik D Schraga, MD, Consulting Staff, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates; Consulting Staff, Permanente Medical Group, Kaiser Permanente, Santa Clara Medical Center
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Howard A Bessen, MD, Professor of Medicine, Department of Emergency Medicine, UCLA School of Medicine; Program Director, Harbor-UCLA Medical Center
Howard A Bessen, MD is a member of the following medical societies: American College of Emergency Physicians
Disclosure: Nothing to disclose.

CME Editor

John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center
John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Chief Editor

Erik D Schraga, MD, Consulting Staff, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates; Consulting Staff, Permanente Medical Group, Kaiser Permanente, Santa Clara Medical Center
Disclosure: Nothing to disclose.

 
 
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