The normal range for urine sodium is about 40 to 220 mmol/L. A low urine sodium is anything less than 40 mmol/L. A high urine sodium is anything more than 220 mmol/L.

Causes of low urine sodium

Virtually all causes of low urine sodium is pathologic. These include:

  • Renal failure
  • Pre-renal AKI
  • Pre-renal azotemia
  • Glomerulonephritis
  • Nephrotic syndrome
  • Hepatorenal syndrome
  • Hypovolemic hyponatremia

Causes of high urine sodium

Physiologic causes of high urine sodium include:

  • Diuretic therapy
  • Excessive salt intake

Pathologic “renal” causes of high urine sodium include:

  • Acute tubular necrosis
  • Post-obstructive diuresis
  • Salt-wasting nephropathy
  • Interstitial nephritis from NSAIDs

Pathologic “extra-renal” causes of high urine sodium include:

  • Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)
  • Hepatic failure
  • Hypothyroidism
  • Adrenal insufficiency
  • Congestive heart failure (CHF)

References and links

Fractional Excretion of Sodium — Calculate by QxMD