Urine sodium
The amount of sodium (salt) in the urine, measured to work out why the blood sodium or fluid balance is off. It shows whether the kidney is holding onto salt (suggesting the body senses low volume) or letting it go, which helps sort out low sodium and some kidney problems.
What it measures
Urine sodium measures how much sodium the kidneys are putting into the urine, usually on a spot sample. Unlike most tests it has no fixed 'normal' range, because a healthy kidney varies urine sodium widely to match salt intake and the body's needs — so it is interpreted in a specific clinical situation rather than as high or low in the abstract. Its value is as a window into what the kidneys are doing. When the body senses low blood volume — from dehydration, blood loss, or conditions like heart failure and cirrhosis where the effective circulation is reduced — the kidneys conserve salt, and urine sodium is low. When salt is being lost inappropriately — from certain kidney or adrenal problems, or diuretic drugs — urine sodium is higher despite the body needing to hold on. This makes it a key test in two situations: working out the cause of a low blood sodium (hyponatremia), where it helps separate volume depletion from the syndrome SIADH, and assessing acute kidney injury, where a low urine sodium points to a kidney straining under poor blood flow rather than damaged kidney tissue. It is often paired with creatinine to calculate the fractional excretion of sodium.
What a high value can mean
- Salt loss through the kidney — diuretic drugs, certain kidney tubular problems, or adrenal insufficiency (Addison's).
- SIADH — in the context of a low blood sodium, a urine sodium that is not low supports this diagnosis.
- Acute kidney injury from kidney tissue damage — as opposed to poor blood flow.
What a low value can mean
- The kidney conserving salt — the body senses low effective volume: dehydration, blood or fluid loss, heart failure or cirrhosis.
- In acute kidney injury — a low urine sodium points to reduced blood flow to the kidney rather than direct kidney damage.
When to discuss with a doctor
Urine sodium is a doctor's tool used to interpret a specific problem — most often a low blood sodium or acute kidney injury — rather than a test to act on directly. In a low blood sodium, it helps sort out whether the person is volume-depleted (kidneys conserving salt, urine sodium low) or has SIADH or salt loss, which changes treatment completely — and treating a low sodium the wrong way, or too fast, can be harmful. In kidney injury, it helps distinguish a kidney short of blood flow from one that is damaged. It is always read alongside the blood sodium, hydration status and the clinical picture. Mediora.AI can show urine sodium alongside blood sodium and osmolality so the pattern is visible together, but this test is interpreted within a clinical assessment by your doctor.