uNa

Sodium in Urine

Urinalysis

What is Sodium in Urine?

Sodium is the body's primary extracellular electrolyte, playing a central role in regulating blood volume, blood pressure, fluid balance, and nerve and muscle function. The kidneys are the master regulators of sodium balance, constantly adjusting how much sodium is reabsorbed from filtered blood back into circulation and how much is excreted in the urine. This regulation is mediated by hormones including aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP), which respond to changes in blood volume and pressure to keep sodium levels within a narrow range.

A urine sodium test measures how much sodium the kidneys are excreting and provides critical diagnostic information about volume status, kidney function, and the cause of electrolyte abnormalities—particularly hyponatremia (low blood sodium), which is the most common electrolyte disorder in hospitalized patients. The test can be performed on a spot urine sample or a 24-hour collection. Spot urine sodium is most useful in acute clinical scenarios, while 24-hour sodium excretion reflects total daily sodium intake and is used for dietary assessment and chronic disease management.

Why It Matters

Urine sodium is one of the most valuable tests for evaluating hyponatremia, acute kidney injury, and volume status in both outpatient and hospital settings. In hyponatremia, urine sodium distinguishes between different causes: low urine sodium (<20 mEq/L) suggests the body is retaining sodium because of volume depletion, heart failure, or cirrhosis, while high urine sodium (>40 mEq/L) points toward SIADH, adrenal insufficiency, or kidney disease. In acute kidney injury, urine sodium helps differentiate prerenal azotemia (where kidneys are underperfused but structurally intact) from intrinsic kidney damage. This distinction directly impacts treatment decisions.

Normal Reference Ranges

GroupRangeUnit
Adults (24-hour)40–220mEq/day
Spot urine (variable)20–40mEq/L

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High uNa Levels Mean

Common Causes

  • High dietary salt intake
  • SIADH (syndrome of inappropriate antidiuretic hormone)
  • Adrenal insufficiency (Addison disease)
  • Salt-wasting nephropathy
  • Diuretic use
  • Cerebral salt wasting
  • Acute tubular necrosis (recovering phase)

Possible Symptoms

  • Often reflects underlying condition rather than sodium excretion itself
  • Headache and confusion (if hyponatremia develops)
  • Nausea and vomiting
  • Muscle cramps
  • Low blood pressure (if volume depleted)
  • Fatigue

What to do: High urine sodium in the setting of hyponatremia suggests SIADH, adrenal insufficiency, or renal salt wasting. Your doctor will check serum and urine osmolality, cortisol levels, and thyroid function to identify the cause. Treatment for SIADH includes fluid restriction and sometimes medications like tolvaptan. Adrenal insufficiency requires hormone replacement. If high urine sodium simply reflects high dietary intake, reducing salt consumption is recommended to protect blood pressure and cardiovascular health.

What Low uNa Levels Mean

Common Causes

  • Volume depletion or dehydration
  • Congestive heart failure
  • Liver cirrhosis with ascites
  • Nephrotic syndrome
  • Low dietary sodium intake
  • Prerenal acute kidney injury
  • Aldosterone excess (primary or secondary)

Possible Symptoms

  • Signs of the underlying condition (edema in heart failure, ascites in cirrhosis)
  • Thirst
  • Dizziness upon standing
  • Reduced urine output
  • Dry mucous membranes
  • Rapid heart rate

What to do: Low urine sodium indicates the kidneys are retaining sodium in response to perceived volume depletion—whether actual (dehydration, hemorrhage) or effective (heart failure, cirrhosis). Treatment depends on the cause: volume-depleted patients need intravenous fluids, while patients with heart failure or cirrhosis need sodium and fluid restriction along with diuretics. Low urine sodium in the setting of acute kidney injury suggests prerenal causes that may respond to volume resuscitation, potentially avoiding more serious kidney damage.

When Is uNa Testing Recommended?

  • When evaluating hyponatremia (low blood sodium)
  • In the workup of acute kidney injury to determine the cause
  • When assessing volume status in hospitalized patients
  • To monitor dietary sodium intake and compliance
  • When SIADH or adrenal insufficiency is suspected
  • In the management of heart failure or cirrhosis

Frequently Asked Questions

When blood sodium is low (hyponatremia), urine sodium helps narrow the cause. A urine sodium below 20 mEq/L suggests the kidneys are appropriately retaining sodium because the body perceives low volume—seen in dehydration, heart failure, and cirrhosis. A urine sodium above 40 mEq/L indicates the kidneys are excreting sodium despite low blood levels, which is "inappropriate" and points toward SIADH, adrenal insufficiency, thyroid disease, or kidney disorders. This is one of the first tests ordered in any hyponatremia workup because it fundamentally divides causes into two categories with different treatments.
Yes, a 24-hour urine sodium collection is considered the gold standard for estimating dietary salt intake. Since the kidneys excrete about 90% of ingested sodium, 24-hour urine sodium closely reflects dietary consumption. To convert: 1 gram of salt (sodium chloride) contains approximately 17 mEq of sodium. So a 24-hour urine sodium of 170 mEq corresponds to roughly 10 grams of salt per day. The recommended daily sodium intake is less than 2,300 mg (100 mEq), and many health organizations recommend less than 1,500 mg for those with hypertension. Spot urine samples are less reliable for dietary assessment.
Fractional excretion of sodium (FENa) is a calculation that compares how much sodium the kidneys filter versus how much they actually excrete, expressed as a percentage. It requires both blood and urine sodium and creatinine levels. FENa less than 1% suggests prerenal acute kidney injury (the kidneys are underperfused but intact, so they aggressively retain sodium). FENa greater than 2% suggests intrinsic kidney damage (the tubules cannot properly reabsorb sodium). This distinction is critical in hospitalized patients with rising creatinine, as prerenal injury often responds to fluids alone, while intrinsic injury may require different management.

Related Biomarkers

NaSodiumuClChloride in UrineuKPotassium in UrineCrCreatinine

Want your uNa levels analyzed?

Upload your lab results for an instant AI-powered breakdown of all your biomarkers.

Upload Lab Results →

Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.