Urine Sodium, 24-Hour
The total sodium that left your body in urine over 24 hours, which mostly follows how much sodium you eat.
AI-verified against cited sources. Awaiting expert reviewAlso called U Na 24h, UNa 24h, 24h UNaLOINC 2956-1
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What it is
Sodium is the main salt in your blood and body fluids. Your kidneys adjust how much sodium they release in urine to match what you take in, so a full day of urine closely follows how much sodium you eat. A small amount is lost in sweat and stool. This test measures all the urine you collect over 24 hours and reports the total. A full-day total smooths out the large swings in sodium between day and night.
Why it matters
Clinicians use this number to see how much sodium you actually take in, and to learn whether your kidneys are holding on to sodium or letting too much go. It is used when looking into blood pressure, salt and fluid balance, and in kidney stone evaluations. The World Health Organization suggests that adults keep sodium intake under 2,000 mg a day (about 87 mmol, or 5 grams of salt). The worldwide average is more than double that.
If it’s low
A low total often means you ate little sodium, or that your body held on to sodium because you lost fluid. It can also be seen with heart, liver or kidney conditions that make the body hold on to salt and water. A low result from a low-salt diet is expected.
Common causes
- A low-sodium diet
- A collection that missed some urine
- Dehydration, heavy sweating, vomiting or diarrhea
- Heart failure
- Cirrhosis of the liver
- Chronic kidney disease or kidney failure
- Adrenal glands making too much aldosterone, a hormone that holds on to sodium
What can help
- Think back over the collection day and tell your clinician if any urine was missed
- Ask your clinician whether your result fits your diet and how much you drank
- Ask whether your blood sodium and kidney tests should be checked too
If it’s high
A high total often reflects a lot of sodium in the food and drink around the time of the collection. Water pills (diuretics) can also make the kidneys release more sodium. Less often, the kidneys or adrenal glands lose too much sodium. Many things can cause this, and your clinician can put it in context with your blood tests.
Common causes
- A high-salt diet, such as packaged, processed and restaurant foods
- Water pills (diuretics) or other medicines that make the kidneys release sodium
- Salt or saline fluids given in a hospital
- Adrenal glands that make too little of the hormones that hold on to sodium
- Kidney conditions that waste salt (salt-losing nephropathy)
- Diabetic ketoacidosis
What can help
- Ask your clinician whether the result fits how you usually eat
- Read food labels, since most dietary sodium comes from packaged and restaurant foods
- Ask whether any of your medicines could be affecting the result
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 22–328 mmol/24 h. Source: Mayo Clinic Laboratories, ARUP Laboratories, MedlinePlus Medical Encyclopedia (NIH National Library of Medicine), Quest Diagnostics.
- 18+ (this one applies)22–328 mmol/24 h
Sources: Mayo Clinic Laboratories, ARUP Laboratories, MedlinePlus Medical Encyclopedia (NIH National Library of Medicine), Quest Diagnostics
What can affect your result
- Diet: the amount of sodium you eat is the biggest factor
- Fluids, sweating, vomiting and diarrhea
- Medicines, especially water pills
- Time of day: sodium leaves faster during the day, and the overnight rate is only about a fifth of the daytime peak
- Collection accuracy: missed or extra urine changes the total
- Day-to-day variation: one day is a snapshot of your usual intake
- Incomplete or over-long collections give a falsely low or high total. Labs record the total volume and collection time, and some also check urine creatinine to judge whether the collection was complete.
- Water pills (diuretics) and some other medicines change how much sodium the kidneys release. Tell your clinician about every medicine you take.
- A very salty or very low-salt diet in the days around the test changes the result.
- Heavy sweating, vomiting or diarrhea during the collection lowers urine sodium.
- Preservatives matter: Mayo accepts several for this test but not nitric acid, sodium carbonate or toluene. Use the container your lab gives you.
A full 24-hour collection. Empty your bladder at a set time and flush that urine, then collect all urine after that, including the first urine at the same time the next day. The total reflects the day you collected, and it follows what you ate and drank around that day.
When to talk to a clinician
A urine sodium result alone is rarely urgent. Contact your clinician promptly if you have repeated vomiting, severe weakness or confusion, or if the lab flagged your blood sodium. Call 911 or your local emergency number for a seizure or fainting.
Questions you could ask
- What is this test being used to find out in my case?
- Does this match how much salt I usually eat, or could a medicine be involved?
- Should my blood sodium and kidney tests be checked too?
- Could a low-salt diet or fluid loss explain this?
- Was my collection complete, and should we repeat it?
Questions people ask
Does this number tell me how much salt I eat?
Roughly, yes. When your intake is steady, most of the sodium you eat leaves in your urine, so the daily total follows your intake. One day can be off, though. Sweating, vomiting, diarrhea, water pills or a missed collection can all change it.
How do I turn mmol of sodium into milligrams?
Multiply by 23. A result of 100 mmol is about 2,300 mg of sodium. Table salt is about 39% sodium by weight, so 2,300 mg of sodium comes from roughly 5.8 g of salt.
Why do labs print such different ranges?
Because the result follows what you eat and drink. Mayo prints 22–328 mmol/24 h, Quest 52–380, ARUP 51–286, and MedlinePlus lists 40–220 for adults. Use the range on your own report. A result outside it may just reflect a very salty or very low-salt day.
Show the science and sources
Units
- 1 mmol/24 h = 1 mmol/24 h
- 1 mmol/24 h = 1 mEq/24 h
- 1 mmol/24 h = 22.99 mg/24 h
Open the Urine Sodium 24h unit converter
Is a change real?
Urine Sodium 24h naturally varies about 28.7% from test to test in the same healthy person. Between two results from the same lab, a rise of 140% or more, or a fall of 58% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Desirable Biological Variation Database specifications, 2014 update (Minchinela J, Ricos C, et al.; the 'Ricos database', a compilation of median published CVI/CVG).
For clinicians and researchers
In a steady state, 24-hour urinary sodium excretion approximates dietary sodium intake, less small losses in sweat and stool. Excretion has a marked diurnal rhythm, and Mayo notes that the overnight rate is only about 20% of the daytime peak, so a full 24-hour collection captures the whole cycle better than a spot sample. Mayo's interpretive comment ties kidney sodium loss (diuretic therapy, salt-losing nephropathy, adrenal insufficiency) to urinary sodium usually above 20 mEq/L, and notes that in volume-depleted states a value below 10 mEq/L points to non-kidney sodium loss. Sodium is measured by ion-selective electrode (Mayo: indirect potentiometry; Quest: ISE). Published intervals differ widely and reflect diet, not assay disagreement: Mayo 22–328 mmol/24 h (18 years and older, none for younger), Quest 52–380 mmol/24 h, ARUP 51–286 mmol/d, MedlinePlus 40–220 mmol/day. 1 mmol of sodium is 22.99 mg, and 1 mEq equals 1 mmol. Table salt (NaCl) is about 39% sodium by weight. WHO recommends under 2 g sodium per day for adults. Collection completeness is the main source of error, so total volume, collection time and urine creatinine should be checked. In acute kidney injury or hyponatremia work-ups, a spot urine sodium and fractional excretion of sodium are used instead. Quest lists increased excretion with high salt intake, adrenal failure, diabetic acidosis, salt-losing kidney disease and dehydration, and decreased excretion in heart failure, excessive sweating, diarrhea, pyloric obstruction, malabsorption and primary aldosteronism.
LOINC 2956-1 (primary), 21527-7, 21525-1. Specimen: urine-24h.
Sources
- NAU - Sodium, 24 Hour, Urine, Mayo Clinic Laboratories
- Sodium, Urine (test 0020851), ARUP Laboratories
- Sodium urine test, MedlinePlus Medical Encyclopedia (NIH National Library of Medicine)
- Sodium, 24-Hour Urine without Creatinine (test code 11317), Quest Diagnostics
- Salt reduction (fact sheet), World Health Organization
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.