Chemistry / Electrolytes
BicarbonateHCO₃⁻
Principal extracellular buffer; the metabolic axis of acid-base.
Sample
Serum (calculated from total CO₂ on chemistry panels)
Clinical reference range
22 to 29 mmol/L
Adult
Conv: 22–29 mmol/L
Biology
What it measures
Generated by renal H⁺ secretion and consumed buffering acid loads. Directly proportional to pH on the Henderson-Hasselbalch equation.
Clinical use
Why we order it
Detect metabolic acidosis (low) or alkalosis (high); guides further ABG interpretation.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Always pair with anion gap; isolated low HCO₃ with normal AG points to GI or renal HCO₃ loss.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Vomiting
- ↑Diuretics
- ↑Hyperaldosteronism
- ↑Compensated respiratory acidosis
Causes of LOW
- ↓DKA, lactic acidosis, salicylate, methanol/ethylene glycol (high AG)
- ↓Diarrhea, RTA (normal AG)
- ↓Compensated respiratory alkalosis
Pitfalls
Pre-analytic & interpretation traps
- !Total CO₂ on a venous chemistry panel underestimates true HCO₃ by ~2 mmol/L.
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