What is the normal range for urine sodium?

Normal Range for Urine Sodium

The normal range for urine sodium in a 24-hour collection is typically between 40-220 mmol/day, with values above 20 mmol/L in random specimens generally indicating normal renal sodium handling. 1

Understanding Urine Sodium Measurements

• 24-hour urine sodium collections provide the most accurate assessment of sodium balance and excretion, with urinary sodium excretion in healthy individuals closely matching sodium intake minus approximately 10 mmol/day of non-urinary losses 1
• Random "spot" urine sodium measurements are less reliable than 24-hour collections but can provide useful clinical information when interpreted correctly 1
• A spot urine sodium/potassium ratio greater than 1 correlates with a 24-hour sodium excretion >78 mmol/day with approximately 90% accuracy 2

Clinical Significance of Urine Sodium Values

Low Urine Sodium (<20 mmol/L)

• Suggests sodium retention, which may occur in:
  • Volume depletion/hypovolemia 2
  • Hepatorenal syndrome (typically <10 mEq/L) 2
  • Heart failure 1
  • Prerenal azotemia 2

Moderate Urine Sodium (20-40 mmol/L)

• May be seen in:
  • Recent diuretic use 2
  • Partial volume depletion 2
  • Early acute kidney injury 2

Normal to High Urine Sodium (>40 mmol/L)

• Typically indicates:
  • Normal renal function 3
  • Adequate sodium intake 1
  • Diuretic effect 2
  • Sodium-wasting nephropathy 1

Very High Urine Sodium (>140 mmol/L)

• Almost always associated with normal renal function, even when diuretics are used 3
• May serve as a biomarker of normal/improving renal function and better outcomes in critically ill patients 3

Factors Affecting Urine Sodium Levels

• Dietary sodium intake: Average intake in many countries ranges from 3-5 g/day (130-217 mmol/day), which is reflected in urinary excretion 4, 5
• Kidney function: Impaired renal function can significantly alter sodium excretion patterns 3
• Diuretic use: Can artificially increase urine sodium despite volume depletion 2
• Race: Studies have shown differences in urinary electrolyte excretion between racial groups, with African Americans sometimes excreting less potassium than whites on similar diets 6
• Sodium intake level: The body adapts to varying sodium intake by adjusting glomerular filtration rate and fractional sodium reabsorption in both proximal and distal tubules 7

Clinical Applications

• In patients with cirrhosis and ascites, urinary sodium excretion >78 mmol/day suggests the patient is excreting more sodium than the typical restricted intake of 88 mmol/day 2
• For diagnosis of hepatorenal syndrome, urine sodium <10 mEq/L is a supportive finding 2
• In the assessment of acute kidney injury, fractional excretion of sodium (FENa) <1% suggests prerenal causes including hepatorenal syndrome, while FENa >1% suggests structural causes like acute tubular necrosis 2
• Fractional excretion of urea (FEUrea) <28.16% may help differentiate hepatorenal syndrome from other causes of acute kidney injury 2

Clinical Pitfalls to Avoid

• Not accounting for the effects of diuretics, which can artificially increase urine sodium excretion despite volume depletion 2
• Relying solely on spot urine sodium values rather than 24-hour collections when making important clinical decisions 1
• Failing to consider that patients who have recently received diuretics may have higher urine sodium levels despite having conditions that would normally cause sodium retention 2
• Not recognizing that very low urine sodium values (<20 mmol/L) may signify threat to normal kidney function and worse prognosis even with normal serum creatinine 3