Hyponatremia | |
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Other names | Hyponatraemia, low blood sodium, hyponatræmia |
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Sodium, as shown on the periodic table | |
Specialty | Nephrology |
Symptoms | Decreased ability to think, headaches, nausea, poor balance, confusion, seizures, coma[1][2][3] |
Types | Low volume, normal volume, high volume[4] |
Diagnostic method | Serum sodium < 135 mmol/L[3] |
Differential diagnosis | Ethanol intoxication or withdrawal, high protein levels, high blood fat levels, high blood sugar[5][6] |
Treatment | Based on underlying cause[4] |
Frequency | Relatively common[6][7] |
Hyponatremia or hyponatraemia is a low concentration of sodium in the blood.[4] It is generally defined as a sodium concentration of less than 135 mmol/L (135 mEq/L), with severe hyponatremia being below 120 mEq/L.[3][8] Symptoms can be absent, mild or severe.[2][9] Mild symptoms include a decreased ability to think, headaches, nausea, and poor balance.[1][3] Severe symptoms include confusion, seizures, and coma;[1][2][9] death can ensue.[10]
The causes of hyponatremia are typically classified by a person's body fluid status into low volume, normal volume, or high volume.[4] Low volume hyponatremia can occur from diarrhea, vomiting, diuretics, and sweating.[4] Normal volume hyponatremia is divided into cases with dilute urine and concentrated urine.[4] Cases in which the urine is dilute include adrenal insufficiency, hypothyroidism, and drinking too much water or too much beer.[4] Cases in which the urine is concentrated include syndrome of inappropriate antidiuretic hormone secretion (SIADH).[4] High volume hyponatremia can occur from heart failure, liver failure, and kidney failure.[4] Conditions that can lead to falsely low sodium measurements include high blood protein levels such as in multiple myeloma, high blood fat levels, and high blood sugar.[5][6]
Treatment is based on the underlying cause.[4] Correcting hyponatremia too quickly can lead to complications.[5] Rapid partial correction with 3% normal saline is only recommended in those with significant symptoms and occasionally those in whom the condition was of rapid onset.[4][6] Low volume hyponatremia is typically treated with intravenous normal saline.[4] SIADH is typically treated by correcting the underlying cause and with fluid restriction while high volume hyponatremia is typically treated with both fluid restriction and a diet low in salt.[1][4] Correction should generally be gradual in those in whom the low levels have been present for more than two days.[4]
Hyponatremia is the most common type of electrolyte imbalance, and is often found in older adults.[11][12] It occurs in about 20% of those admitted to hospital and 10% of people during or after an endurance sporting event.[3][5] Among those in hospital, hyponatremia is associated with an increased risk of death.[5] The economic costs of hyponatremia are estimated at $2.6 billion per annum in the United States.[13]
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