• How does the urine sodium test help determine the cause of low blood sodium?

The test helps identify the cause of hyponatremia. Low urine sodium levels (typically less than 20 mmol/L) often suggest non-renal causes like vomiting or diarrhea, while levels above 40 mmol/L may indicate that the kidneys are losing sodium due to certain syndromes or the use of diuretics.

• Why is this test used for patients taking diuretics?

The test is used to evaluate how the body responds to diuretic medications and to monitor patients who have complex electrolyte disorders while taking these treatments.

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Urine Sodium Test

A test measuring salt and fluid balance in your body, helping doctors accurately diagnose causes of dehydration, heart failure, or renal tubule disorders.

Trusted medical contentUpdated: 04-09-2026Views: 23LHL-3235

About this service

This test measures the concentration of sodium (Na⁺) in urine, indicating how well the renal tubules are handling the reabsorption and excretion of this essential ion. Urine sodium excretion depends on the balance between dietary intake, extracellular fluid volume, and levels of regulatory hormones (such as aldosterone and atrial natriuretic peptide - ANP). It is often ordered along with serum sodium (Serum Na) to evaluate the cause of any abnormalities in its levels (hyponatremia or hypernatremia) and to differentiate between renal (kidney-related) and non-renal causes.

Conditions and notices

Fasting is not required

Fasting is not required, but recent salt intake should be recorded if possible.

A random urine sample or a 24-hour urine sample may be requested depending on the diagnostic purpose. Follow your doctor's instructions carefully.

If you request a 24-hour sample, the completion of the collection is a prerequisite for accuracy.

Inform your doctor about all medications, especially diuretics (water pills), and any supplements.

For a baseline assessment, your doctor may ask you to follow a sodium-restricted diet prior to the examination.

Frequently Asked Questions

Short answers to the FAQs published with this service.

• What does the Urine Sodium test measure?

It measures the concentration of sodium in the urine to evaluate how the kidneys handle its reabsorption and excretion.

• Is fasting required for this test?

No, fasting is not necessary for the urine sodium test.

• What is FENa in the context of this test?

It is the fractional excretion of sodium, used to help differentiate between different causes of acute kidney failure.

• Why is urine sodium monitored in heart failure patients?

Urine Sodium Test

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Conditions and notices

Frequently Asked Questions

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