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July 26, 2008

All About Hyponatremia

All About Hyponatremia


Hyponatremia is an abnormally low concentration of sodium in your blood.

When your blood sodium is too low, your cells malfunction — causing swelling. In chronic hyponatremia, sodium levels drop gradually over several days or weeks — and symptoms are typically moderate. In acute hyponatremia, sodium levels drop rapidly — resulting in potentially dangerous effects, such as rapid brain swelling, which can result in coma and death.

Hyponatremia occurs when the sodium in your blood is diluted by excess water. Hyponatremia may result from medical conditions that impair excretion of water from your body, or by a significant increase in water consumption, such as by athletes competing in marathons and other high-endurance events.

Treatment focuses on the underlying condition and may include intravenous fluids and medications.


Hyponatremia symptoms may include:

* Nausea and vomiting
* Headache
* Confusion
* Lethargy
* Fatigue
* Appetite loss
* Restlessness and irritability
* Muscle weakness, spasms or cramps
* Seizures
* Decreased consciousness or coma


Sodium is a key component of your body. It's an electrolyte and helps carry nerve impulses between cells. It helps maintain normal blood pressure, it's essential for your nervous system to accomplish muscle movement, and it regulates the fluids in and around your cells.

Normal blood plasma contains between 136 and 145 milliequivalents per liter (mEq/L) of sodium. Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L.

When the sodium levels in your blood become too low, excess water enters your cells — causing them to swell. This swelling is especially dangerous to your brain because it's confined by your skull and unable to expand.

Hyponatremia is typically the result of a medical condition that impairs the excretion of water from your body, or the excessive consumption of water. The imbalance between sodium and water in your blood may occur in three primary ways:

* Hypervolemic hyponatremia. In hypervolemic hyponatremia, excess water — commonly the result of kidney failure, heart failure or liver failure — dilutes the sodium concentration, causing low sodium levels.
* Euvolemic hyponatremia. Normal water levels combined with low sodium levels (commonly due to chronic health conditions, cancer or certain medications) can lead to euvolemic hyponatremia.
* Hypovolemic hyponatremia. In hypovolemic hyponatremia, your water and sodium levels are both low. This may occur, for example, when exercising in the heat without replenishing your fluids or with marked blood loss.

Hyponatremia causes may include:

* Consuming excessive water during exercise. Because you lose sodium through sweat, drinking too much water during endurance activities, such as marathons and triathlons, can dilute the sodium content of your blood.
* Hormonal changes due to adrenal gland insufficiency (Addison's disease). Your adrenal glands produce hormones that help maintain your body's balance of sodium, potassium and water.
* Hormonal changes due to an underactive thyroid (hypothyroidism). Hypothyroidism may result in a low blood sodium level.
* Diuretics (water pills) — especially thiazide diuretics. Diuretics work by making your body excrete more sodium in urine.
* Syndrome of inappropriate anti-diuretic hormone (SIADH). In this condition, high levels of the anti-diuretic hormone (ADH) are produced, causing your body to retain water instead of excreting it in your urine.
* Primary polydipsia. In this condition, your thirst increases significantly, causing increased fluid intake.
* Certain medications. Some medications, such as some antidepressants and pain medications, can cause you to urinate or perspire more than normal.
* Chronic, severe vomiting or diarrhea. This causes your body to lose fluids and electrolytes, such as sodium.
* Dehydration. In dehydration, your body loses fluids and electrolytes.
* Diet. Consuming a low-sodium diet combined with excessive water intake for prolonged periods can disturb the proper balance between sodium and fluids in your blood.
* Cirrhosis. Liver disease can cause fluids to accumulate in your body.
* Kidney problems. Kidney failure and other kidney disease may render your body unable to efficiently remove excess fluids from your body.
* Congestive heart failure. The condition causes your abdomen and lower extremities to retain fluids.

Risk factors

The following factors may increase your risk of hyponatremia:

* Age. Low blood sodium is more common in older adults. This is due to age-related changes and increased prevalence of chronic disease that may impair your body's normal sodium balance.
* Sex. Hyponatremia is more common in women than in men.
* Diet. You may be at an increased risk of hyponatremia if you are following a low-sodium diet, especially if combined with diuretic intake.
* Intensive physical activities. People who take part in marathons, ultramarathons, triathlons and other long-distance, high-intensity activities are at an increased risk of hyponatremia.
* Climate. Not being acclimated to hot weather can increase the amount of sodium you lose through sweating during exercise.
* Conditions that impair your body's water excretion. Medical conditions that may increase your risk of hyponatremia include kidney disease, syndrome of inappropriate anti-diuretic hormone (SIADH) and heart failure, among others.

When to seek medical advice

If you take part in high-intensity activities, such as marathons, have a medical condition that increases your risk for hyponatremia, or have other risk factors for hyponatremia and you exhibit the signs and symptoms of low blood sodium, see your doctor.

Tests and diagnosis

Your doctor will take a medical history and conduct a physical examination. He or she will likely ask about your signs and symptoms, and whether you've experienced recent vomiting, diarrhea, or other significant fluid loss.

Because the signs and symptoms of hyponatremia are nonspecific and occur in many conditions, it's impossible to diagnose the condition based on a physical exam alone. To confirm low blood sodium, laboratory tests — including blood tests and possibly urine tests — are necessary.


Untreated, acute hyponatremia — the form of hyponatremia in which sodium levels fall rapidly — can lead to rapid swelling of your brain, resulting in coma and death.

Treatments and drugs

Hyponatremia treatment is directed at the underlying cause, if it can be identified and corrected.

If you have moderate, chronic hyponatremia due to the use of diuretics or excessive water consumption, your doctor may advise you to temporarily cut back on fluids or adjust your diuretic use to increase the level of sodium in your blood.

If you have severe, acute hyponatremia, more aggressive treatment is required. Options include:

* Intravenous fluids. Your doctor may recommend intravenous (IV) administration of a sodium solution to raise the sodium levels in your blood. This often requires a stay in the hospital.
* Medications. You may take medications to manage the signs and symptoms of hyponatremia, such as headache, nausea and seizures.
* Hormone injections. If adrenal insufficiency (Addison's disease) is the cause of hyponatremia, you may undergo hormone injections to correct the condition.


The following measures may help you prevent hyponatremia:

* Treat associated conditions. Getting treatment for conditions that contribute to hyponatremia, such as adrenal insufficiency, can help prevent you from experiencing low blood sodium.
* Educate yourself. If you have a medical condition that increases your risk of hyponatremia or you take diuretic medications, be aware of the signs and symptoms of low blood sodium.
* Take precautions during high-intensity activities. Guidelines from the International Marathon Medical Directors Association advise runners to drink only as much fluid as they lose due to sweating during a race. Athletes should drink no more than 31 ounces of water per hour during extended exercise.
* Consider drinking sports beverages during demanding activities. Ask your doctor about replacing water with sports beverages that contain electrolytes when participating in endurance events such as marathons, triathlons and other demanding activities.
* Drink water in moderation. Drinking water is vital for your health, so make sure you have a sufficient daily intake of fluids. But don't overdo it.

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