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Hyponatremia - Causes, Symptoms, Diagnosis, and Treatment

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Hyponatremia is a condition characterized by a low sodium level in the blood. Read this article to learn about its causes, symptoms, and treatment.

Written by

Dr. Asna Fatma

Medically reviewed by

Dr. Kaushal Bhavsar

Published At September 21, 2022
Reviewed AtNovember 28, 2022

What Is Hyponatremia?

Hyponatremia is a condition with low sodium concentration in the blood. It happens when the sodium concentration falls below 135 mEq/L. Sodium is vital for several functions in the body. Sodium is required to maintain a fluid balance and blood pressure regulation, and it is required for nerves and muscles to work correctly. Usually, sodium should be between 135 to 145 mEq/L in blood, and any value below that is considered hyponatremia or sodium deficiency in the blood. Moreover, sodium concentration below 120 mEq/L is regarded as severe hyponatremia. When the blood sodium level goes very low, water starts entering and pooling in the cells, making them swell, and this swelling can be very dangerous, especially to the brain.

What Causes Hyponatremia?

Hyponatremia is caused mainly when the amount of sodium in the fluids outside the cells drops below average, and extracellular water moves inside the cells to balance the levels. This results in swelling of the cells with excess fluids. The following conditions cause the imbalance of water to sodium:

  1. Euvolemic Hyponatremia: An increase in total body water characterizes euvolemic hyponatremia, but sodium content stays the same.

  2. Hypervolemic Hyponatremia: Both water and sodium content in the body increase, but the water gain is more.

  3. Hypovolemic Hyponatremia: Water and sodium are lost from the body, but more sodium is lost.

The following reasons can cause hyponatremia:

  • The kidneys fail to get rid of the extra fluids from the body.

  • Congestive heart failure causes excess fluid to build up in the body.

  • Liver cirrhosis (a chronic liver disease in which healthy liver tissues are replaced by scar tissues).

  • Burns.

  • Diarrhea.

  • Excess sweating.

  • Vomiting.

  • Diuretics are antihypertensive drugs that increase urination and cause low sodium. Antidepressants and painkillers are also used for symptomatic relief.

  • Excess thirst or primary polydipsia causes increased water intake leading to low sodium.

  • Prolonged exercise and sweating along with drinking water without electrolytes.

  • Pancreatitis.

  • Addison's disease or congenital adrenal hyperplasia.

  • Hypothyroidism.

  • Beer potomania (excess intake of beer along with poor diet causes fatigue, dizziness, and muscular weakness).

  • Pregnancy.

What Are the Symptoms of Hyponatremia?

In the case of mild hyponatremia, there might be no apparent signs and symptoms for a long time. The severity of the symptoms depends on how fast and how low the levels drop.

Symptoms of mild hyponatremia are:

  1. Altered posture.

  2. Altered gait.

  3. Falling a lot.

  4. Reduced attention.

  5. Impaired cognition and ability to learn and understand.

Symptoms of moderate to severe hyponatremia are:

  1. Nausea and vomiting.

  2. Headache.

  3. Low blood pressure.

  4. Loss of appetite.

  5. Fatigue.

  6. Lethargy.

  7. Irritability and confusion.

  8. Muscle weakness and spasms.

  9. Cramps.

  10. Seizures.

  11. Short-term memory loss.

  12. Hyponatremic encephalopathy.

How Is Hyponatremia Diagnosed?

Hyponatremia can be diagnosed by taking a patient's detailed medical history, physical examinations, and laboratory tests. A blood examination is a standard procedure to evaluate sodium concentration in the blood. In addition, medical history is taken to determine if the patient is hypovolemic, euvolemic, or hypovolemic. The following tests are done:

  • Comprehensive Metabolic Panel: This test measures 14 different substances, including sodium, potassium, glucose, calcium, etc.

  • Osmolality Blood Test: This test checks the fluid to particle balance in the body.

  • Urine Osmolality Test: This test measures the concentration of sodium in the urine. A urine osmolality value of less than 100 mOsm/ kg is indicative of suppressed antidiuretic hormone.

  • Urine Sodium: Normal sodium level in urine is 20 mEq/L in a random urine sample.

How Is Hyponatremia Treated?

The step in treating hyponatremia is determining the underlying cause of the condition, and the urgency of the treatment is determined by the severity of the symptoms. For example, in the case of acute hyponatremia with swelling in the brain, the patient requires immediate medical aid to prevent comatose (condition of prolonged unconsciousness) and death.

  • Fluid replacement is the primary step in treating hyponatremia. Around five mmol/L of sodium is increased over the course of four hours in case of severe symptoms. However, increasing sodium concentration rapidly can lead to osmotic demyelination syndrome(ODS) or central pontine myelinolysis (CPM). Therefore, increasing the serum sodium level by more than ten mmol/L in a day is not recommended.

  • If the cause is adrenal insufficiency, then Hydrocortisone is given, which is a steroid hormone replacement.

  • Water intake is limited in case of hypervolemic hyponatremia.

  • Medications causing low sodium (like Diuretics) may be discontinued to relieve the symptoms.

  • In case of low sodium intake through diet, a balanced diet with an adequate amount of sodium is advised.

  • Sodium retaining drugs may be given.

What Are the Complications of Hyponatremia?

In severe cases, hyponatremia can cause the following complications:

  1. Herniation of the brain due to squeezing the brain across the internal structures of the skull.

  2. Hyponatremic encephalopathy is increased pressure on the skull due to swelling in brain cells.

  3. Non-cardiogenic accumulation of fluid in the lungs.

  4. Respiratory arrest.

  5. Seizures.

  6. Brain stem compression.

  7. Increased chances of osteoporosis and fracture due to altered bone metabolism.

  8. Comatose (period of prolonged unconsciousness).

  9. Death.

What Is the Prognosis of Hyponatremia?

The prognosis of hyponatremia depends on the underlying cause of the condition. In addition, hyponatremia that develops over a more extended period, also known as chronic hyponatremia, has a better prognosis than hyponatremia which progresses very quickly, also known as acute hyponatremia.

Who Is More Affected by Hyponatremia?

Hyponatremia is the most prevalent form of water-electrolyte imbalance. Women are more affected by this condition than men. Older people and patients admitted to the hospital are also more frequently affected by hyponatremia.

How Can Hyponatremia Be Prevented?

Hyponatremia can be managed and prevented by taking a few simple precautions in our everyday life. It is important to monitor drugs that might be causing low sodium in the blood; it is also essential to check on medications that cause water retention. Moreover, sodium deficiency in the diet can easily be prevented by incorporating a tiny amount of table salt in the diet. In addition, exercise-associated hyponatremia can be easily controlled by not doing a high-intensity workout and drinking water with electrolytes in between exercises.


Hyponatremia is defined as the presence of a low level of sodium in the blood. Although the condition might seem like a very mild problem and the symptoms may be subtle, it can cause some severe complications and even death if not treated on time. Symptoms of hyponatremia depend on the underlying cause of the condition, and the severity of the symptoms depends on whether it is acute or chronic hyponatremia. The diagnosis and treatment of the state are simple yet effective. It is highly recommended to consult a physician urgently if several similar symptoms are noticed.

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Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)


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