Sodium test
Quick answer: A sodium test measures sodium, a salt that controls fluid balance and nerve and muscle function, in your blood or urine. It is ordered in routine panels, with confusion, weakness, vomiting, dehydration, kidney or heart problems, and on medicines such as diuretics.
- SampleBlood or urine
- TakesAbout 5 minutes for blood; up to 24 hours for urine
- Before the testNo special preparation is usually needed for blood; for the 24-hour urine test, you will be given a container and collection instructions.
How the test is done
- 1For blood, a vein is cleaned and a sample is drawn
- 2For spot urine, you pass a sample into a container
- 3For 24-hour urine, you collect all urine over a full day
- 4Blood and urine sodium may be read together
What your results can mean
Reading your report
Normal ranges differ between labs, so compare your result with the range printed on your report and discuss it with your doctor.
If the result is outside the usual range
A low sodium can be seen with drinking too much water, vomiting, diarrhoea, diuretics, heart, liver or kidney problems, and some hormone conditions. A high sodium is usually seen with dehydration or not drinking enough.
Who usually has this test
People with confusion, weakness, vomiting or dehydration, older adults on diuretics, and those with heart, liver or kidney disease.
Risks and aftercare
A blood draw may cause minor bruising, while urine collection carries no risk.
Names and options
Also called: serum sodium, Na test, urine sodium
Options
- Serum
- 24-hour urine
- Spot urine
Listed by the hospital as
- SODIUM, SERUM
- SODIUM, 24 HRS URINE
- SODIUM SPOT URINE
Questions about this test
What are the symptoms of low sodium?
Mild low sodium may cause no symptoms, while lower levels can cause headache, nausea, tiredness, confusion and, if severe, seizures. Older people are more at risk.
Why is urine sodium tested?
Urine sodium helps doctors work out why blood sodium is abnormal, for example whether the kidneys are losing too much salt or the body is holding on to water.
Can drinking a lot of water lower sodium?
Yes. Drinking very large amounts of water in a short time can dilute sodium in the blood. This is uncommon in healthy people who drink to thirst.
Related tests
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.