Metabolic Alkalosis Urine Chloride Interpreter
Metabolic Alkalosis Urine Chloride Interpreter
Sort a metabolic alkalosis into chloride-responsive — vomiting, gastric drainage, diuretics that have worn off — and chloride-resistant — mineralocorticoid excess, a diuretic still acting, Bartter and Gitelman syndromes, severe potassium or magnesium depletion — using a spot urine chloride and the blood pressure. The page explains why urine chloride, not urine sodium, is the test.
Chloride-responsive or chloride-resistant?
Urine chloride + blood pressure → cause of alkalosisA 34-year-old with a week of vomiting: bicarbonate 38 mmol/L, potassium 2.8 mmol/L, blood pressure 98/60, urine sodium 46 mmol/L, urine chloride 8 mmol/L, no diuretics.
Two splits
Urine chloride 25 or more → chloride-resistant on both readings; then blood pressure: high → mineralocorticoid excess; normal → Bartter, Gitelman, hidden diuretic, severe K or Mg depletion
- chloride-responsive
- corrects when chloride is replaced; also called saline-responsive
- chloride-resistant
- does not correct with chloride; also called saline-unresponsive
- diuretic acting
- raises urine chloride while it acts, so the test must wait until it has worn off
Worked example
A 34-year-old with a week of vomiting: bicarbonate 38 mmol/L, potassium 2.8 mmol/L, blood pressure 98/60, urine sodium 46 mmol/L, urine chloride 8 mmol/L, no diuretics.
No diuretic acting, so the urine chloride can be read
Urine chloride 8 mmol/L is below 20 → chloride-responsive on both published cut-offs
Note the urine sodium of 46: bicarbonate spilling into the urine has carried sodium with it, so urine sodium would have wrongly suggested the patient was not depleted
Treat with sodium chloride and potassium chloride
Urine chloride cut-offs in print
| Source | Chloride-responsive | Chloride-resistant |
|---|---|---|
| Merck Manual Professional (Lewis, 2025) | Below 20 mmol/L | Above 20 mmol/L |
| Rose and Post, 5th edition (2001) | Below 25 mmol/L | Not stated in the part read |
| Leiva-Murillo et al, Cleve Clin J Med 2025 | Below 20 mmol/L suggests vomiting or gastric loss | — |
Why urine chloride, not urine sodium
A metabolic alkalosis needs two things: something that generated the extra bicarbonate, and something that stops the kidney getting rid of it. The kidney normally excretes surplus bicarbonate quickly, so an alkalosis that persists is being maintained, usually by chloride depletion, potassium depletion or excess mineralocorticoid. The spot urine chloride separates the first from the rest, and that split also decides treatment: chloride-responsive alkalosis corrects when chloride is replaced, while chloride-resistant alkalosis does not.
Urine sodium is the usual marker of volume depletion, but it misleads here. During active vomiting the filtered bicarbonate exceeds what the tubule can reclaim, and bicarbonate in the urine has to be accompanied by a cation, so sodium and potassium are dragged out with it. A vomiting, volume-depleted patient can therefore have a urine sodium of 40 or more while the urine chloride, which has no reason to be excreted, stays below 20 mmol/L. The same bicarbonaturia is why vomiting causes renal potassium loss (see the hypokalaemia cause interpreter).
Two things falsely raise the urine chloride. A diuretic still acting forces chloride out, so wait until it has worn off; after that, the same patient’s low urine chloride reveals the depletion the diuretic caused. And the published cut-off is not agreed — 20 mmol/L in one current text, 25 mmol/L in a standard textbook — so values between the two are borderline. Above them, blood pressure divides the chloride-resistant causes: hypertension points to mineralocorticoid excess, while a normal or low blood pressure points to Bartter or Gitelman syndrome, covert diuretic use, or severe potassium or magnesium depletion. This page supports clinical judgement and does not replace it.
Frequently asked questions
What urine chloride means chloride-responsive metabolic alkalosis?
Below 20 mmol/L in current Merck text; some textbooks use below 25 mmol/L. It points to vomiting, gastric drainage or diuretics that have worn off, and the alkalosis should correct with sodium chloride.
Why is urine chloride better than urine sodium in metabolic alkalosis?
Because bicarbonate spilling into the urine carries sodium with it, so urine sodium can be high in a volume-depleted, vomiting patient. Urine chloride stays low.
What causes chloride-resistant metabolic alkalosis?
With hypertension, mineralocorticoid excess such as primary aldosteronism. With normal blood pressure, Bartter or Gitelman syndrome, a diuretic still acting or taken covertly, and severe potassium or magnesium depletion.
Related calculators
References
- Lewis JL III. Metabolic alkalosis. Merck Manual Professional Edition. Revised March 2025.
- Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders. 5th ed. McGraw-Hill; 2001:551–558.
- Leiva-Murillo EA, Bechtold-Javier E, Candela-Parrilla P, Matas-García A. Finding the cause of severe hypokalemia: a 4-step approach. Cleve Clin J Med. 2025;92(12):748–756.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.