Last Updated: November 01, 2023
Medically reviewed by NKF Patient Education Team
About hyponatremia (low sodium level in the blood)
Hyponatremia (hi-poh-nay-tree-me-uh) is when the level of sodium in your blood is lower than normal.
Sodium is an important mineral that helps balance the amount of fluid (water) in your body. It also helps your nerves and muscles to work properly. When the sodium level in your blood is too low, extra water moves into your cells and makes them swell (get bigger). This can be dangerous, especially in the brain where there is not a lot of room to expand.
The kidney connection
Your kidneys play an active role in keeping your sodium and fluid levels balanced. People with more advanced stages of chronic kidney disease (CKD) may have a hard time balancing their fluid and blood sodium levels. This can lead to hyponatremia.
Signs and symptoms
Most people with mild hyponatremia may not have any symptoms. If symptoms are present, it is usually when the level of sodium in your blood goes very low or drops very fast. These symptoms can include:
- Nausea and/or vomiting
- Headache
- Muscle weakness, spasms (twitching), or cramps
- Low blood pressure
- Dizziness when standing up
- Low energy or fatigue
- Loss of appetite
- Restlessness or bad temper
More serious symptoms can happen in severe cases when the level of sodium in your blood is extremely low. These include:
- Altered mental status (severe confusion)
- Hallucinations
- Decreased consciousness
- Seizures
- Coma
Interesting fact: in most cases, hyponatremia (low blood sodium) is more closely related to how much fluid (water) is in your body than not getting enough sodium in your diet.
There are many reasons why your water and sodium levels can be out of balance. Some of the reasons that are more common for people living with kidney disease include:
- Acute kidney injury (AKI), advanced stages of chronic kidney disease (CKD), and kidney failure: the kidneys have trouble getting rid of extra fluid from the body which dilutes the blood
- Thiazide diuretics (water pills), such as hydrochlorothiazide (HCTZ) or chlorthalidone: can cause the body to get rid of too much sodium in the urine (especially at higher doses)
- Heart failure: extra fluid can build up in the body and dilute the blood
- Severe vomiting or diarrhea: can cause a lot of sodium and fluid loss
- Polydipsia (excessive thirst): can cause a person to drink too many fluids and dilute the blood
Other causes of hyponatremia that may not be directly related to kidney diseases include:
- Extreme hyperglycemia (very high blood sugar): extra fluid can build up in the blood to counteract the high level of sugar
- Cirrhosis (advanced liver disease): extra fluid can build up in the body and dilute the blood
- Syndrome of inappropriate antidiuretic hormone secretion (SIADH): a medical condition where your body holds on to too much water and removes too much sodium in the urine
- Medications, such as some antidepressants, seizure medicines, or cancer medicines: may cause your body to hold extra water and/or lose too much sodium in urine or sweat
Complications
Hyponatremia that develops slowly over time and/or is only mildly decreased is not likely to cause complications, especially if treated promptly.
On the other hand, sudden hyponatremia (dramatic drop in less than 48 hours) and/or severely decreased sodium levels can cause serious problems if left untreated, including:
- rhabdomyolysis (life-threatening muscle breakdown)
- altered mental status (severe confusion)
- seizures
- coma
- death
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Diagnosis
Tests
A simple blood test is used to measure the level of sodium in your blood.
A normal blood sodium level is between 135 and 145 milliequivalents/liter (mEq/L). So, hyponatremia is when the level of sodium in your blood is below 135 mEq/L.
Remember, a low sodium level can be caused by many factors. So, your healthcare professional will likely order other tests and ask you questions about your medical history and recent routine to get a complete picture.
Other tests may include serum creatinine, glucose (sugar), potassium, carbon dioxide, triglycerides, and/or urine tests. When looked at together, your healthcare professional can provide you with custom guidance for resolving the issue.
Treatment
Treatment is based on the cause and severity of your hyponatremia.
Sodium levels falling just below 135 mEq/L may not warrant treatment - close follow-up and/or a recheck may be all that is needed. Prompt treatment is most important for people who have sudden hyponatremia (dramatic drop in less than 48 hours) and/or severely decreased levels.
Hyponatremia treatment is highly customized and requires medical supervision. Do not attempt any treatment approaches on your own without talking to your healthcare professional first.
Your healthcare professional may recommend one or more of the following treatment approaches:
- focus on the condition(s) causing the hyponatremia, like heart failure, cirrhosis, diabetes, or kidney failure
- lower the amount of liquids you eat and/or drink (also known as fluid restriction)
- adjust your medication dose and/or switch to a different medication (if the hyponatremia is a medication side effect)
- adjust your dialysis settings to take more fluid off with each session (if you are on dialysis)
- give a dose of sodium through your vein (intravenous or IV)
- add a medication that helps your body remove extra water while also holding on to sodium, such as tolvaptan or conivaptan (also known as aquaretics)
- add more salt (sodium) to your diet (not a common approach for people with kidney diseases)
Preparing for your appointment
Questions to ask
- What risk factors do I have for hyponatremia?
- How concerned should I be about hyponatremia?
- What steps can I take to prevent hyponatremia?
- Is there any reason for me to limit how many fluids I eat/drink in a day? If so, what is the maximum amount recommended for me?
- What is my “dry weight”? What should I do if my weight at home is much higher or lower than my “dry weight”?
