What defines hyponatremia?

Hyponatremia is defined as a sodium deficit in the body, specifically characterized by a serum sodium concentration that is lower than the normal range, which is typically below 135 mmol/L. Sodium is a vital electrolyte that plays a crucial role in maintaining fluid balance, transmitting nerve impulses, and muscle function. When there is a significant deficit of sodium, it can disrupt these physiological processes and lead to symptoms like headache, confusion, seizure, and even coma in severe cases.

Fluid overload can be a contributing factor to hyponatremia, as excess water can dilute the sodium concentration in the blood, but it does not define the condition itself. Similarly, dehydration leads to a deficit of water but often results in a higher concentration of sodium and would not be classified as hyponatremia. Sodium excess is clearly the opposite of what hyponatremia represents. Understanding the balance of sodium and water in the body is essential in evaluating and diagnosing electrolyte imbalances.