Table 194.1Classification of Hyponatremia

Clinical featuresLaboratory features
Hyponatremia with expanded extracellular fluid volume (excess, total body sodium)
 Congestive heart failureEdema, rales, gallop rhythmUrine Na+ <10 mEq/L
 CirrhosisAscitesBUN to creatinine ratio often >10:1
 Nephrotic syndromeEdemaHyperuricemia in congestive heart failure
Hyponatremia with contracted extracellular fluid volume (reduced total body sodium)
Causes: renal loss of sodiumUrine Na+ may be elevated
May have hypokalemic alkalosis
 Overtreatment with diuretics
 Sodium restriction in chronic renal failureBUN to creatinine ratio may be >10:1
 Addison's disease
Causes: extrarenal lossesNo edemaUrine Na+ low
May have postural hypotensionBUN to creatinine ratio may be >10:1
 Vomiting, diarrhea
 Extensive trauma
Hyponatremia with normal or slightly expanded ECF volume (normal or slightly reduced total body sodium)
 Syndrome of inappropriate antidiuretic hormone releaseNo edemaUrine Na+ >30 mEq/L
 Drugs that impair water excretionLow BUN
Low uric acid level (<4.5 mg/dl)

From: Chapter 194, Serum Sodium

Cover of Clinical Methods
Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition.
Walker HK, Hall WD, Hurst JW, editors.
Boston: Butterworths; 1990.
Copyright © 1990, Butterworth Publishers, a division of Reed Publishing.

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