What is a normal sodium level?
About 133 to 146 mmol/L, depending on your lab. But two people on 128 can need very different help. How fast the level fell can matter as much as the number.
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What is a normal sodium level?
At South Tees NHS lab, normal blood (serum) sodium is 133 to 146 mmol/L. Royal Berkshire gives a typical range of 135 to 145 and says normal varies a little between labs.
So read the range printed next to your result. The “Na” on your report is sodium’s chemical symbol.
- Below 120 mmol/LSevere low. RUH Bath: hospital care.
- 120 to just under 133 mmol/LLow. Usually GP care if you have no symptoms and aren’t dried out.
- 133 up to 146 mmol/LNormal at South Tees NHS lab.
- Above 146 mmol/LHigh. At 155 or more, hospital may be needed.
Sources: South Tees NHS; RUH Bath; NHS Scotland lab guide
Just under the line? The Society for Endocrinology says severe symptoms are unlikely above 130.
Low but feel fine? RUH Bath advises GPs to repeat a new low result soon, to rule out a fast fall.
Ask your GP when your repeat test should be.
What causes low sodium?
Sodium is the main salt in the fluid around your cells. Your level depends on how much water you hold, as well as how much sodium.
Think of squash in a jug. It tastes weak if there’s too little squash or too much water. So a low result doesn’t always mean you need more salt.
| Body water | Causes |
|---|---|
| Too little (dried out) | Water tablets (diuretics), vomiting or diarrhoea, kidney disease, Addison’s disease (when your body makes too little of some key hormones). |
| Too much (fluid build-up) | Heart failure, long-term liver disease, a kidney condition called nephrotic syndrome. |
| About right | Some medicines, long-term low salt intake, heavy drinking, drinking huge amounts of fluid, a hormone problem that makes you hold water (SIADH), or rarely an underactive thyroid. |
Sources: RUH Bath; Royal Berkshire
Medicines on RUH Bath’s list include water tablets, ACE inhibitors (a type of blood pressure tablet) and SSRI antidepressants. It also lists carbamazepine for epilepsy, antipsychotics and stomach acid tablets called PPIs.
Never stop or change a prescribed medicine without your prescriber.
Some lows aren’t what they seem. High blood sugar can lower sodium. Very high blood fats or protein can make it read falsely low, and the lab checks for those.
Ask your GP whether your blood sugar was checked too.
Why can two people on 128 need different help?
Your symptoms depend on your level and how quickly it fell. That’s the speed of the fall.
Person A drifted down to 128 over months. Their brain has had time to adapt, so they may have no symptoms.
Person B dropped from 140 to 128 in a day, after drinking lots of water at a marathon. RUH Bath calls a fall of more than 10 in under 48 hours significant, even before symptoms show.
So the same 128 can mean different help. Person A can usually be checked by their GP. A fall like Person B’s is treated as significant.
| Level | Symptoms |
|---|---|
| Mild | Poor appetite, headache, feeling or being sick, low energy. |
| Moderate | Personality change, muscle cramps and weakness, confusion, clumsy movements. |
| Severe | Drowsiness and fits (seizures). |
Source: Royal Berkshire
Mild effects are easy to miss. RUH Bath links a level under 130 to slower thinking, even when people don’t notice it.
Had a fast drop and feel unwell? Get help from 111 or 999.
What does high sodium mean?
High means above your lab’s range, such as above 146 at South Tees. The most common cause is dehydration. This matters most in older people and care home residents.
It can cause thirst, then confusion.
Passing lots of urine can also push it up. Causes include undiagnosed or poorly controlled diabetes, or a condition called diabetes insipidus that makes your urine too weak.
A sample can read falsely high if liquid from another blood tube got into it. So the lab advises a repeat test.
Steady at 146 to 148, well and not dried out? That may mean nothing.
See how dehydration affects blood tests, then ask your GP about a repeat.
What happens next, and do salt tablets help?
What your GP usually does after a low result
- 1
Repeat test
Soon for a new low, to rule out a fast fall.
- 2
Medicines
A possible cause may be stopped, then sodium rechecked.
- 3
Body water
Are you dried out or holding fluid?
- 4
Find the cause
Tests may cover kidneys, sugar, thyroid and a morning hormone test (cortisol).
Source: RUH Bath
After a medicine change, RUH Bath rechecks sodium within days if it’s quite low, or in 2 weeks if mildly low.
Salt tablets aren’t a home fix. Treatment depends on the cause: fluids if you’re dried out, drinking less if a hormone makes you hold water. Raising sodium too fast can harm the brain, so doctors raise it slowly.
For everyday eating, the NHS says adults should have no more than 6g of salt a day. That limit is about food, not about fixing a low result. More on electrolyte drinks.
What to do after an abnormal sodium result
- Compare your result with the range your lab printed next to it.
- Book the repeat test your GP asks for, even if you feel well.
- Take a list of every medicine you take to your GP appointment.
- Never stop or change a prescribed medicine without your prescriber.
- Don’t start salt tablets or cut your drinks unless your GP or hospital tells you to.
- Get help from 111 or 999 if you get new confusion, drowsiness, being sick or fits.
Sources: RUH Bath; Royal Berkshire
When to speak to a GP
Most people with low sodium have no symptoms, especially when it’s mild and came on slowly. Get help if:
- You get new or worse symptoms after a low result: poor appetite, headache, feeling or being sick, low energy, personality change or confusion, cramps or weakness, clumsiness, drowsiness or fits. Royal Berkshire tells its patients to call 111 or 999.
- Your sodium is below 120, or low with symptoms or with signs you’re dried out. RUH Bath admits these to hospital.
- It fell by more than 10 in under 48 hours, for example after drinking a lot at a marathon.
- Your sodium is 155 or more, rising fast, or you can’t drink enough. Hospital care should be considered.
- Your sodium stays under 130. RUH Bath generally advises GPs to look for a cause.
Sodium usually comes as part of a U&E test. See U&E results explained and the kidney function test.