What Is Considered Dangerously Low Sodium? An Expert Guide to Hyponatremia

December 3, 2025 •

4 min read

According to research, up to 20% of hospitalized patients experience hyponatremia, or low blood sodium. So, what is considered dangerously low sodium? Dangerous levels of low sodium, a condition known as hyponatremia, are defined as serum sodium concentrations below 125 mEq/L, and can rapidly lead to life-threatening complications like cerebral edema and seizures.

Quick Summary

Hyponatremia, or low blood sodium, is defined as a serum sodium concentration below 135 mEq/L. Levels below 125 mEq/L are severe and can cause significant neurological issues. Symptoms include headache, confusion, seizures, or coma, depending on the severity and onset. Treatment is determined by the underlying cause and how quickly the condition develops, always requiring medical supervision.

Key Points

Severity Scale: Hyponatremia is defined as a serum sodium level below 135 mEq/L, but severe cases occur below 125 mEq/L and pose the highest risk.
Critical Threshold: Neurological symptoms become prominent when sodium falls below 115 mEq/L, and this is considered extremely dangerous.
Symptom Spectrum: Manifestations range from mild (headache, fatigue) to severe (seizures, coma, cerebral edema), with acute drops being particularly hazardous.
Diverse Causes: Hyponatremia can result from various factors, including excessive water intake, certain medications (e.g., diuretics), heart or kidney failure, and SIADH.
Careful Treatment: Treatment involves addressing the underlying cause and carefully raising sodium levels, often with IV saline. Correcting levels too quickly can cause severe, permanent brain damage (ODS).
Risk Groups: Older adults, endurance athletes, and individuals with underlying health conditions or those on specific medications are at higher risk.

Understanding the Sodium Scale: When is it Low?

Sodium is a crucial electrolyte that helps regulate fluid balance, nerve function, and blood pressure. The normal range for blood sodium is 135 to 145 milliequivalents per liter (mEq/L). When levels drop below this range, the condition is called hyponatremia. This condition is classified into different levels of severity based on the measured serum sodium concentration:

Mild Hyponatremia: Serum sodium is between 130–134 mEq/L. Symptoms are often subtle or absent in this stage, but can include mild fatigue or malaise.
Moderate Hyponatremia: Serum sodium is between 125–129 mEq/L. Symptoms become more noticeable and may include persistent headache, nausea, and disorientation.
Severe or Profound Hyponatremia: Serum sodium is less than 125 mEq/L. This is when the condition becomes truly dangerous and neurological symptoms are likely to appear.

Defining Dangerously Low Sodium Levels

The threshold for a truly dangerous situation is a serum sodium concentration below 125 mEq/L, but overt neurological symptoms typically become apparent when the level falls below 115 mEq/L. The danger arises from osmotic shifts in fluid, where excess water moves into the brain cells, causing them to swell (cerebral edema). The speed of the sodium drop is also a critical factor; an acute (rapid) drop is far more dangerous than a gradual, chronic one.

The Alarming Signs and Symptoms of Severe Hyponatremia

Symptoms of low sodium often mirror those of dehydration, but they result from the internal fluid imbalance rather than just water loss. They can range from mild and non-specific to severe and life-threatening.

Early to Moderate Symptoms

Nausea and vomiting
Headache
Fatigue or low energy
Muscle weakness, cramps, or spasms
Irritability and restlessness
Loss of appetite

Severe and Critical Symptoms

As sodium levels continue to fall, the brain's swelling can lead to severe neurological issues requiring emergency care:

Severe confusion or altered mental status
Decreased consciousness or lethargy
Hallucinations
Seizures
Coma
Brainstem herniation
Cardio-respiratory arrest

What Causes Sodium Levels to Plummet?

Low sodium is not caused by a simple lack of salt in the diet but by an imbalance of water and sodium in the body. The causes are diverse and can be classified based on the body's overall fluid status.

Common Causes of Hyponatremia

Excessive Water Intake: This is often seen in endurance athletes who over-hydrate with water without replacing electrolytes lost through sweat. It can also occur in individuals with psychiatric conditions like psychogenic polydipsia.
Medical Conditions: Various diseases can cause hyponatremia by affecting the body's fluid regulation. These include heart failure, liver cirrhosis, and kidney failure.
Medications: Certain drugs, particularly diuretics (often called "water pills"), some antidepressants (SSRIs), and specific pain medications, can interfere with sodium regulation.
Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH): This condition causes the body to produce too much antidiuretic hormone (ADH), leading to water retention. SIADH can be triggered by neurological disorders, pulmonary diseases, or certain medications.
Vomiting or Diarrhea: Severe or prolonged gastrointestinal fluid loss depletes both sodium and water. If fluid replacement consists only of plain water, it can lead to further sodium dilution.
Adrenal Insufficiency: Disorders like Addison's disease affect the adrenal glands' ability to produce hormones that help regulate sodium.
Other Factors: Severe burns, certain cancers (especially lung cancer), hypothyroidism, and illicit drug use (MDMA/Ecstasy) can all contribute to hyponatremia.

Comparison: Normal vs. Dangerously Low Sodium


Feature	Normal Sodium Balance	Dangerously Low Sodium (Severe Hyponatremia)
Serum Sodium Level	135–145 mEq/L	< 125 mEq/L
Symptom Onset	None, as balance is maintained.	Can be acute (<48 hrs) or chronic (slowly developing).
Common Symptoms	Absence of electrolyte-related issues.	Headache, nausea, fatigue, muscle cramps, confusion.
Critical Symptoms	None.	Seizures, coma, brain swelling, cardiac arrest.
Underlying Cause	Effective kidney function and balanced fluid intake.	Excessive water intake, medical conditions, medication side effects.
Risk of Complications	Minimal.	High risk of permanent brain damage or death, especially in acute cases.

Managing and Treating Dangerously Low Sodium

Treatment for hyponatremia is highly specific to the cause, severity, and speed of onset. All forms of severe hyponatremia require prompt medical attention and should never be self-treated. In a hospital setting, treatment may include:

Intravenous Fluids: For severely symptomatic or acute cases, a hypertonic (concentrated) saline solution may be administered via IV to slowly raise sodium levels. This is done with extreme care to prevent rapid overcorrection, which can cause severe and irreversible brain damage (osmotic demyelination syndrome).
Fluid Restriction: In cases of excess body water (euvolemic or hypervolemic hyponatremia), doctors may restrict fluid intake to help the body excrete excess water.
Addressing the Root Cause: If the condition is a result of another illness, such as heart or kidney failure, treatment will focus on managing that underlying disease.
Medication Adjustment: If a medication is the cause, the dosage may be adjusted or the patient may be switched to an alternative drug.
Symptom Management: Medications may be used to control acute symptoms such as seizures or nausea while sodium levels are corrected.

Conclusion: The Importance of Immediate Medical Care

Hyponatremia is a common but potentially life-threatening electrolyte imbalance. Knowing what is considered dangerously low sodium is the first step towards recognizing a medical emergency. While mild cases may be asymptomatic or cause vague symptoms, a severe drop in sodium can lead to catastrophic neurological damage, including cerebral edema and seizures. Due to the complex nature of treatment and the serious risks involved, immediate medical attention is essential for anyone experiencing signs of severe hyponatremia, such as confusion, seizures, or loss of consciousness. Proper diagnosis and carefully managed treatment can prevent permanent damage and ensure a full recovery.

For more in-depth medical information on hyponatremia, consult the resource from the National Institutes of Health: Hyponatremia - StatPearls - NCBI Bookshelf.

It is important to remember that this information is for educational purposes only and is not a substitute for professional medical advice. Always consult a healthcare provider for diagnosis and treatment.

Frequently Asked Questions

The normal and healthy range for blood sodium is typically between 135 and 145 milliequivalents per liter (mEq/L). Levels below this indicate hyponatremia.

If your sodium level is too low, extra water moves into your cells and causes them to swell. This is particularly dangerous in the brain, where swelling can lead to severe confusion, seizures, coma, and even death.

Yes, a sodium level of 120 mEq/L is considered severe hyponatremia. It is a dangerously low level that requires urgent medical attention, especially if accompanied by symptoms like confusion or seizures.

Dangerously low sodium levels are often caused by an excess of water relative to total body sodium. This can result from excessive fluid intake, certain medications like diuretics, underlying medical conditions such as heart or kidney failure, severe vomiting or diarrhea, and SIADH.

The first signs of low sodium can be subtle and include nausea, headache, fatigue, and muscle cramps. As levels drop, symptoms become more severe.

Treatment for dangerously low sodium involves correcting the underlying cause and cautiously raising the sodium levels. This may include intravenous hypertonic saline in severe, symptomatic cases, coupled with careful monitoring to prevent rapid overcorrection and brain damage.

Yes, if left untreated, severe hyponatremia can be fatal. The risk is highest with acute, rapid drops in sodium levels that cause dangerous brain swelling. In some patient populations with severe hyponatremia (<105 mEq/L), mortality can be over 50%.

Acute hyponatremia develops in less than 48 hours and poses a higher risk of serious neurological complications like brain swelling. Chronic hyponatremia develops over a longer period, allowing the brain to adapt, but still carries risks like falls and cognitive issues.