Serum Chloride

Physiology

Background
1. Chloride is an important negative ion (anion) in the maintenance of Fluid and Electrolyte Balance
2. Chloride is also an important constituent of gastric fluid
Chloride and Bicarbonate Balance
1. Serum Chloride concentrations are inversely proportional to serum bicarbonate levels
  1. Serum Chloride increases when serum bicarbonate decreases
  2. Serum Chloride decreases when serum bicarbonate increases
2. Chloride is the most common extracellular anion, and increases when bicarbonate anions are deficient
  1. Renal mechanisms maintain chloride when serum bicarbonate is low (acidosis)
Chloride also follows Sodium concentrations
1. Chloride typically increases and decreases in line with Sodium concentration
Chloride and Red Blood Cell (and Hemoglobin) Relationship
1. Peripheral tissue CO2 enters Red Blood Cell (RBC)
  1. In the RBC, CO2 combines with H2O to form Hydrogen Ion and bicarbonate (via carbonic anhydrase)
  2. Bicarbonate leaves the RBC
  3. Chloride enters the cell (and Hydrogen Ion binds Hemoglobin)
2. Lung tissue O2 enters Red Blood Cell
  1. Inspired Oxygen combines with Hemoglobin displacing Hydrogen Ion
  2. Hydrogen Ion combines with bicarbonate, forming H2O as well as CO2 which is expired
  3. Chloride leaves the Red Blood Cell
Chloride and Acid-Base
1. Hypochloremic Acidosis
  1. Renal absorption of Sodium and bicarbonate increases when pH decreases (acidosis)
  2. When bicarbonate absorption increases, chloride absorption decreases (ion balance)
  3. Most often, acidosis is accompanied with Hypochloremia (except in cases as below)
2. Hyperchloremic Acidosis
  1. Renal tubules may be unable to secrete Hydrogen Ion
  2. Without Hydrogen Ion, bicarbonate remains in the renal tubule as an anion that cannot be absorbed
  3. Chloride is absorbed instead when bicarbonate cannot be absorbed

Interpretation
Abnormal

Hyperchloremia
1. Increased Serum Chloride
Hypochloremia
1. Decreased Serum Chloride

References

Goldberg (2014) Clinical Physiology, p. 26-7