Kidneys, electrolytes and minerals
Sodium blood test: what a high or low result means
What a sodium blood test measures, what high or low sodium can mean, and what to ask your doctor.
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Explain my results → Available on web, iOS & Android.What is sodium?
Sodium is a mineral, or electrolyte, that helps control the balance of water in your body and keeps your nerves and muscles working. The sodium level in your blood mainly reflects the balance between sodium and water, rather than how much salt you eat. It is part of the U&E (urea and electrolytes) blood test, or a metabolic panel in the US, and appears as Na or Na+.
Why is this test done?
- As part of a routine kidney blood test
- To monitor medicines that can affect sodium, such as water tablets and some antidepressants
- When someone is confused, unwell, vomiting or has diarrhoea
- To monitor heart, liver or kidney conditions
What does a high sodium mean?
A high sodium is called hypernatraemia (hypernatremia in the US). It usually means the body has too little water.
Possible reasons include:
- Dehydration, from not drinking enough, fever, vomiting or diarrhoea
- Some medicines
- Rarely, hormone conditions affecting water balance, such as diabetes insipidus
What does a low sodium mean?
A low sodium is called hyponatraemia (hyponatremia in the US). It is one of the most common blood test findings, especially in older people. Mild cases often cause no symptoms; very low levels can cause confusion or falls.
Possible reasons include:
- Some medicines, especially water tablets (diuretics) and some antidepressants
- Drinking very large amounts of water
- Vomiting or diarrhoea
- Heart, liver or kidney conditions
- Hormone conditions, such as low cortisol (adrenal problems) or a condition where the body holds on to too much water (SIADH)
Why we don't list a "normal range". Reference ranges differ between laboratories and can depend on your age, sex and whether you are pregnant. The range printed next to your result on your own report is the one that applies to you, so use that, and talk to your doctor about what your result means for you.
What can affect your sodium result?
- How much fluid you have drunk
- Medicines, particularly water tablets and some antidepressants
- Vomiting or diarrhoea
- Very high blood sugar or fats, which can affect the measurement
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Try it with your own results → Paste, upload or photograph your results.Questions to ask your doctor
- Could one of my medicines be affecting my sodium?
- Should I change how much I drink?
- Does this explain any of my symptoms, such as confusion or tiredness?
- When will it be checked again?
Frequently asked questions
Does low sodium mean I should eat more salt?
Usually not. Low sodium in the blood is most often caused by too much water relative to sodium, or by medicines, rather than by too little salt in the diet. Follow your doctor's advice rather than adding salt.
Can medicines cause low sodium?
Yes. Water tablets (diuretics) and some antidepressants are common causes. Do not stop a medicine without talking to your doctor first.
Is low sodium dangerous?
Mildly low sodium is common and often causes no symptoms. Very low sodium, or sodium that falls quickly, can cause confusion, falls or seizures and needs prompt medical attention.
Can Patiently AI explain my sodium result?
Yes. Paste your results, or upload a photo, PDF or Word file, and Patiently AI explains them in plain English, sticking to the numbers and ranges on your own report rather than adding its own, and suggests questions to ask your doctor. It is free, needs no account, and removes identifying details on your device first.