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Hyponatremia
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Hyponatremia means having low sodium as measured in the blood, specifically in the serum. A cutoff is used to call it low, and that cutoff can vary slightly from one laboratory to another.
What matters here is not only how much sodium there is, but how much water comes with it. Outside the cells, sodium is the main solute, that is, the main substance dissolved in the fluid. In hyponatremia, the body holds too much water for the amount of sodium it has. It is like salt in a pot with too much water: the proportion is off.
Who keeps that balance in check? Thirst, the kidney through its handling of sodium, and a hormone, vasopressin, also called antidiuretic hormone, which regulates how much water the kidney takes back before it leaves in the urine. When something triggers vasopressin release and more fluid also comes in, hyponatremia can develop.
In brief
Hyponatremia is a low serum sodium concentration; the cutoff may vary slightly depending on the laboratory's reference range.
It results from an excess of total body water relative to total body sodium, the main solute in the extracellular fluid.
Salt in a pot with too much water: the proportion is off.
Sodium is regulated by thirst, renal sodium handling and vasopressin, or antidiuretic hormone, which controls renal water reabsorption; when something stimulates vasopressin release and fluid intake also rises, hyponatremia can develop.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingHyponatremia, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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