人體內鈉離子(Na+)靠細胞間滲透壓活性快速的轉換，與腎臟調節每日鈉離子的排泄，來維持急性與慢性的恆定。然而低血鈉(hyponatremia)主要為水分滯留所導致。低血鈉會增加住院患者的罹病率及死亡率，因此有效的診斷與治療低血鈉是本篇探討的主題。腎臟作為處理水分電解質的終末器官，我們可以藉由觀察腎臟在尿液的表現來作診斷的參考。可以檢測尿液鈉離子的排泄量(sodium (Na+) excretion)、血中滲透壓、及尿液中尿酸的排泄分率等連續的追蹤觀察，加上體液容積變化，而進一步鑑別診斷原發病因種類。低尿液鈉離子排泄可為有效容積不足，多渴症，腸道鈉離子流失或之前腎臟過度排泄所引起。而高尿液鈉離子排泄則通常合併有水通道的增加，賀爾蒙失調，利尿劑使用。低血鈉的治療，一般有限水、給予食鹽水、或抗利尿激素拮抗劑等方式改善水分滯留的現象，當然原發疾病的治療也相當重要。

Sodium ions (Na +) in the body rely on the rapid conversion of osmotic activity between cells, and the kidneys regulate the daily excretion of sodium ions to maintain acute and chronic constant. However, hyponatremia is mainly caused by water retention. Hyponatremia increases the morbidity and mortality of hospitalized patients, leading to dizziness, unconsciousness, and even coma, so how to diagnose and treat hyponatremia is the subject of this article. The kidney is the terminal organ that processes water and electrolytes. We can make a diagnosis by observing the performance of the kidney in urine. Continuous observation of urine sodium excretion (sodium (Na +) excretion), blood osmotic pressure, and urine uric acid excretion rate, plus changes in body fluid volume can further identify the original cause. Low urine sodium ion excretion may be caused by insufficient effective volume, polydipsia, loss of intestinal sodium ions, or previous excessive excretion of the kidneys. The high urine sodium excretion is usually combined with an increase in water channels, hormonal disorders, and diuretic use. The treatment of hyponatremia mainly depends on the degree of hyponatremia, the speed of causing hyponatremia, clinical symptoms, underlying causes, and other related potential risk factors.