Chloride, 24-Hour Urine

Chloride, 24-Hour Urine (urine chloride; chlorides in urine, quantitative) is used to assess disorders of water and electrolyte balance and to complement evaluation of renal function. The test supports the workup of hyperchloremic metabolic acidosis consistent with renal tubular acidosis. In patients with acid–base abnormalities, including metabolic alkalosis, measurement of 24-hour urine chloride aids differential diagnosis and helps judge the impact of diuretic therapy. It is also used to monitor treatment of electrolyte disturbances and adherence to a sodium-restricted diet.

Chloride is a negatively charged electrolyte that works with sodium and potassium to regulate extracellular fluid volume and acid–base balance. It is present in all body fluids, with the highest levels in blood and the extracellular compartment, and changes in chloride frequently mirror changes in sodium. Dietary chloride is derived largely from sodium chloride; absorbed chloride is eliminated mainly in urine and may also be lost through vomiting, diarrhea, or gastrointestinal fistulas. In acid–base disorders, chloride can vary independently of sodium; increased chloride is accompanied by reduced bicarbonate in hyperchloremic metabolic acidosis. Aldosterone enhances sodium reabsorption and thereby indirectly promotes chloride reabsorption. Significant pH deviations resulting from disordered chloride homeostasis can affect multiple organ systems, including both the central and peripheral nervous systems.