The test is often used to determine hydration status and the kidney's ability to conserve or excrete sodium. This test may also be performed to indirectly indicate the function of the adrenal cortex or to detect or monitor conditions that result in abnormal urine sodium levels.
Aldosterone (see the aldosterone test), a hormone produced by the adrenal gland, plays a major role in regulating sodium levels within the body and urine. Specifically, aldosterone increases the reabsorption of sodium in the kidneys at the expense of potassium and hydrogen loss.
Reabsorption of sodium in turn enhances retention of water in body tissues and the blood stream. It is by this means that aldosterone helps maintain plasma volume and blood pressure. Dehydration and conditions that decrease kidney blood flow stimulate aldosterone production.
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