chloride (Cl-) in 24 hour urine

Indications

• evaluation of acid-base disorders
• evaluation of hypokalemia
• diagnosis of renal tubular acidosis

Reference interval

• 110-250 mEq/24 hours

Principle

Chloride is the major extracellular anion. Most ingested chloride is absorbed, & the excess is excreted in the urine.

Chloride reacts with mercuric thiocyanate. The thiocyanate thus released reacts with ferric ion & forms a red ferric thiocyanate complex. The absorbance due to this complex is directly proportional to the chloride concentration in the sample & is measured using a two-filter (452-600 nm) endpoint technique.

Clinical significance

Urine chloride levels are strongly dependent on dietary intake. The measurement of urinary chloride is of clinical value only in patients with persistent metabolic alkalosis who are not receiving diuretic.

Increases

• increased salt intake
• postmenopausal diuresis
• massive diuresis
  • salt-losing nephritis
• potassium deficiency
• adrenocortical insufficiency
• tubulointerstitial disease
• Bartter's syndrome

Decreases

• reduced salt intake
• premenstrual salt & water retention
• hypochloremia
  • vomiting
  • intestinal fistula
  • severe diarrhea
  • excessive sweating
• adrenal hyperplasia
• postoperative chloride retention
• other forms of salt retention
  • edema

Specimen

2 mL aliquot of a 24-hour urine collection. Proper 24 hour urine collection procedure should be followed, & collection container should be refrigerated at 2-6 C during collection. The 24-hour urine collection is well-mixed & then measured in a graduated cylinder. The total volume should be recorded.

More general terms

• 24 hour urine
• chloride (Cl-) in timed urine