Dr. Jeff Hersh explains the cause of hyponatremia, and how it should be treated

Dr. Jeff Hersh

Q: My adult son was having severe nausea and vomiting. He went to the emergency room, where they told him his symptoms were caused by low blood sodium. What is this?

A: Sodium is an important electrolyte that helps maintain the body’s total fluid balance (around two-thirds of our body weight is water), specifically regulating the amount of fluid inside and outside the body’s cells (about two-thirds of the water in the body is inside our cells). Sodium is also key to maintaining the volume of water in the blood stream; of the water not in the cells about two-thirds is interstitial — between the cells. The normal blood sodium concentration is 135 to 145 milliequivalents per liter (mEq/L).

Dr. Jeff Hersh
Dr. Jeff Hersh

The medical word for low sodium levels is hyponatremia. Although it's a fairly common condition, with up to 2% of people having some degree of it, the majority of these patients have only mildly decreased blood sodium. This usually causes no or only minimal symptoms.

But if symptoms do develop from hyponatremia, they are typically non-specific such as nausea/vomiting, headache, fatigue and muscle cramps/weakness. More severe hyponatremia (levels less than 120 mEq/L), particularly if it develops rapidly (defined as occurring over less than 48 hours), can cause confusion, seizures and even lead to death (such as when low blood sodium causes swelling in brain cells).

There are many possible causes of hyponatremia:

  • Imbalance of hormones that control water balance. The most common is the adrenal gland secreting inappropriately elevated ADH (anti-diuretic hormone), called SIADH (syndrome of inappropriate ADH).

  • Certain medical conditions such as kidney issues (such as when kidneys inappropriately secrete too much sodium in the urine; liver issues (such as having decreased albumin production, causing low protein levels in the blood that can compromise blood stream fluid volume); heart failure (such as when insufficient blood being is pumped to the body’s cells, causing the body to react by trying to increase blood volume).

  • Certain medications, such as diuretics.

  • Overwhelming excessive water intake. In someone with normally functioning kidneys, this is pretty hard to do but it can happen. For example, in psychogenic polydipsia (a psychiatric condition), the patient compulsively drinks too much water.

  • Severe fluid and sodium loss, with only water being replaced. For example, a marathon runner on a hot day may lose large volumes of sodium and water through sweating, with only water taken in by the runner.

Hyponatremia is determined by a common blood chemistry test (corrected as needed for confounders, such as excessively high blood glucose). Other tests to evaluate hyponatremia commonly include measurement of sodium concentration in the patient’s urine (to be sure the kidneys are appropriately retaining as much sodium as possible), other organ function tests (such as kidney, liver and even heart tests) and specialized hormone tests (for example, measuring ADH).

For many patients, specifically those without severe or life-threatening complications, the first line treatment is restricting water intake. Adjusting any medications that may be contributing to the hyponatremia, and addressing any underlying conditions that could be contributing, is also indicated.

Patients with severe or life-threatening hyponatremia complications (typically those with a rapid drop in blood sodium, and/or those with certain other risk factors such as recent brain injury or other pathological brain conditions) may require treatment with intravenous fluids that have a high sodium concentration. However, correcting blood sodium too rapidly can itself cause severe issues, potentially even death. So correction of severe hyponatremia must be done carefully, and therefore these patients are hospitalized, often in the intensive care unit.

“An ounce of prevention is worth a pound of cure.” Regular monitoring patients at risk for hyponatremia (such as those on certain medications or with certain medical conditions) is needed. It's also important to teach people who may be involved in activities that can pose a risk of developing hyponatremia (such as someone running a long race, especially on a hot day) to learn about proper hydration.

Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.

This article originally appeared on MetroWest Daily News: Dr. Jeff Hersh says hyponatremia is medical word for low sodium levels

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