Unit Converter
Chloride (Cl)
(Major Extracellular Anion – Key for Acid-Base Balance & Fluid Homeostasis)
Synonyms
- Chloride
- Serum chloride
- Plasma chloride
- Cl⁻ ion
- Extracellular anion
Units of Measurement
- mmol/L
- mEq/L
Since chloride is monovalent (valency = –1):
1 mmol/L = 1 mEq/L
Description
Chloride (Cl⁻) is the major extracellular anion and plays essential roles in:
- Maintaining osmotic balance
- Regulating acid–base status (Cl⁻/HCO₃⁻ exchange)
- Forming gastric hydrochloric acid (HCl)
- Preserving electrical neutrality
- Supporting kidney tubular function
Chloride levels closely follow sodium and water balance, and abnormalities often mirror disorders of:
- Hydration
- Acid-base status
- Kidney function
- Hormonal regulation (aldosterone, ADH)
Physiological Role
- Primary extracellular anion
- Inversely related to bicarbonate (HCO₃⁻)
- Crucial part of anion gap calculations
- Helps form gastric acid via chloride shift
- Affects neuronal and muscle excitability
Clinical Significance
Hyperchloremia (High Chloride)
Usually >108 mmol/L
Major Causes
- Non–anion gap metabolic acidosis
- Diarrhea (loss of bicarbonate)
- Renal tubular acidosis (RTA)
- Diarrhea (loss of bicarbonate)
- Excess saline administration (0.9% NaCl)
- Most common iatrogenic cause
- Causes hyperchloremic acidosis
- Most common iatrogenic cause
- Dehydration
- CKD / Renal failure
- Drugs
- Carbonic anhydrase inhibitors
- Ammonium chloride
- Carbonic anhydrase inhibitors
Symptoms
- Deep, rapid breathing
- Weakness, confusion
- Acidosis manifestations
Hypochloremia (Low Chloride)
Usually <98 mmol/L
Major Causes
- Metabolic alkalosis
- Vomiting
- NG suction
- Diuretics (loop, thiazide)
- Vomiting
- SIADH / Water intoxication
- Adrenal insufficiency (Addison disease)
- Heart failure / Liver cirrhosis
- Dilutional hyponatremia + low Cl⁻
- Dilutional hyponatremia + low Cl⁻
- Chronic respiratory acidosis
- Compensation → low chloride
- Compensation → low chloride
Symptoms
- Tetany (via alkalosis)
- Muscle cramps
- Confusion
- Shallow breathing
Reference Intervals
(Tietz 8E + KDIGO + Mayo + ARUP)
Serum Chloride (Adults & Children)
- 98 – 107 mmol/L
- (Identical in mEq/L)
Critical Values
- <80 mmol/L → severe hypochloremia
- >115 mmol/L → severe hyperchloremia
Unit Meanings
| Unit | Description |
| mmol/L | millimoles per liter |
| mEq/L | milliequivalents per liter (same as mmol/L for Cl⁻) |
Diagnostic Uses
1. Acid–Base Interpretation
Low chloride → metabolic alkalosis
High chloride → non–anion gap metabolic acidosis
2. Renal Disorders
Chloride helps differentiate:
- Renal vs extrarenal bicarbonate loss
- Volume status
- Renal tubular acidosis types
3. Hydration & Electrolyte Disorders
Chloride mirrors sodium and water status.
4. Endocrine Disorders
Low chloride may indicate:
- Addison disease
- Mineralocorticoid deficiency
5. Respiratory Disorders
Chloride falls in chronic respiratory acidosis (compensation).
6. Gastric Disorders
Loss of gastric HCl (vomiting, NG suction) → low chloride.
Analytical Notes
- Serum or plasma acceptable
- Avoid contamination from IV saline lines
- Hemolysis minimal effect
- Modern analyzers use ion-selective electrodes (ISEs)
Clinical Pearls
- Always interpret Cl⁻ with Na⁺, K⁺, HCO₃⁻, and anion gap.
- Hyperchloremia after excessive normal saline → switch to balanced crystalloids.
- Low chloride with metabolic alkalosis almost always means vomiting or diuretic use.
- Correcting chloride often corrects alkalosis (“chloride-responsive alkalosis”).
- Chloride is a stronger predictor of mortality in ICU patients than sodium.
Interesting Fact
The “chloride shift” (Hamburger phenomenon) is the body’s most important mechanism for CO₂ transport - RBCs exchange bicarbonate for chloride during gas exchange.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Electrolytes.
- KDIGO Guidelines - Electrolyte & Acid–Base Disorders.
- Endocrine Society - Mineralocorticoid Disorders.
- Mayo Clinic Laboratories - Serum Chloride.
- ARUP Consult - Fluid & Electrolyte Disorders.
- MedlinePlus / NIH - Chloride Test.