Chloride is the most abundant ion outside of cells. It is important for maintaining osmotic pressure, nerve cell function, and fluid balance. The urine chloride test is used primarily in cases of suspected metabolic alkalosis. Under normal circumstances, sodium and urine are excreted into the urine at a steady, equal rate. Plasma levels of chloride tend to mirror those of sodium (i.e., as sodium levels increase in plasma, chloride levels increase). Nevertheless, urine chloride levels can be used to investigate certain diseases and disorders, though urine chloride levels are rarely measured alone. Most often, they are measured in conjunction with urine pH, sodium, and potassium levels. A urine chloride test may also be ordered along with other labs needed to diagnose metabolic alkalosis and other acid-base disturbances, such as arterial blood gases. Acetazolamide, corticosteroids, NSAIDs, and diuretics can interfere with the test.
Normal Ranges for Urine Chloride:
40-224 mmol/24 hours
In metabolic alkalosis were blood volume is decreased, urine sodium levels may be high while urine chloride levels may be low. Very low levels of urine chloride (less than 10 to 20 mEq/L) generally occur after excessive vomiting or nasogastric suction, diuretic induced alkalosis, and certain other forms of metabolic alkalosis. On the other hand, primary hyperaldosteronism, licorice ingestion, and mineralocorticoid excess syndrome cause low urine chloride levels but generally above 25 mEq/L.
Some specific causes of low urine chloride levels are:
- Metabolic alkalosis
- Sodium retention
- Cushing syndrome
- Decreased salt intake
- Diuretics (thiazide and loop diuretics)
- Excess licorice ingestion (glycyrrhizic acid)
- Primary hyperaldosteronism
- Mineralocorticoid excess syndrome
In metabolic acidosis, the excretion of sodium and potassium in the urine goes down while urine chloride excretion stays the same or increases. Conditions that cause excess sodium excretion in the kidney also cause increased urine chloride, since chloride follows sodium in sodium-chloride co-transporters. Increased sodium chloride intake can also lead to high urine chloride levels as can any situation in which calcium resorption by the kidney is impaired.
Some specific causes of high urine chloride levels are:
- Adrenal insufficiency
- Salt-losing nephropathy
- Polyuria (increased urination)
- Excessive salt intake
- Metabolic acidosis
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