Table 1.

Classifications of hyponatremia

ClassificationCriteriaLimitations of Clinical Utility
Moderate (125–129 mmol/L) versus severe/profounda (<125 mmol/L)Absolute SNa concentrationSymptoms do not always correlate with degree of hyponatremia
Acute versus chronicTime of development (cutoff 48 h)Time of development not always known
Symptomatic versus asymptomaticPresence of symptomsMany symptoms aspecific; chronic hyponatremia may be symptomatic
Hypotonic, isotonic, or hypertonicMeasured serum osmolalityIneffective osmoles (e.g., urea, ethanol) are also measured
Hypovolemic, euvolemic, hypervolemicClinical assessment of volume statusClinical assessment of volume status has low sensitivity and specificity
  • a SNa<125 mmol/L is defined as “severe hyponatremia” by the United States guideline, and as “profound hyponatremia” by the European guideline.7,9