Your Blood Acid-Base Buffer
Bicarbonate is your blood's main buffer against acid. Think of it as an acid sponge—it soaks up excess acid to keep your blood pH in a safe range (7.35-7.45). When bicarbonate is low, acid is winning (metabolic acidosis). When it's high, there's too little acid (metabolic alkalosis). The body will fight hard to keep pH normal.
What is Bicarbonate (CO2/HCO3)?
Bicarbonate (HCO3-) is measured on BMP/CMP as "CO2" (total CO2 content, which is >95% bicarbonate). It's the metabolic component of acid-base balance (vs pCO2 which is respiratory). Part of the anion gap: AG = Na - (Cl + HCO3).
↑ What High Bicarbonate (CO2/HCO3) Means
Metabolic alkalosis—blood is too alkaline. Most commonly from vomiting (losing stomach acid), diuretics, or chronic respiratory acidosis (kidneys compensate by retaining bicarbonate).
Common symptoms:
Muscle twitching, cramps · Confusion · Hand tingling (tetany if severe) · Slow shallow breathing (body retains CO2 to compensate)
↓ What Low Bicarbonate (CO2/HCO3) Means
Metabolic acidosis—acid is accumulating. Causes: diabetic ketoacidosis, lactic acidosis, kidney failure, severe diarrhea, toxin ingestion (methanol, ethylene glycol). The anion gap helps classify the type.
Common symptoms:
Rapid deep breathing (Kussmaul respirations—body blowing off CO2 to compensate) · Fatigue, confusion · Nausea · Severe: cardiac dysfunction, coma
Why It Matters
When normal:
Primary indicator of metabolic acid-base status
Low bicarbonate triggers anion gap calculation
Guides diagnosis of metabolic acidosis and alkalosis
Part of every basic metabolic panel
Risks if abnormal:
Low (<18): significant metabolic acidosis—investigate cause
Very low (<10): severe acidosis—potentially life-threatening
High (>32): significant metabolic alkalosis
Both extremes can cause cardiac arrhythmias
What Can Cause Abnormal Levels?
Lactic Acidosis (low)
25% likelyTissue hypoperfusion (sepsis, shock), severe exercise, metformin toxicity.
Vomiting/NG suction (high)
25% likelyLoss of gastric acid (HCl) leaves excess bicarbonate.
DKA (low)
Ketoacid accumulation consumes bicarbonate.
Renal Failure (low)
Kidneys can't excrete acid or regenerate bicarbonate.
Diarrhea (low)
GI tract secretes bicarbonate. Diarrhea loses it.
Diuretics (high)
Contraction alkalosis from volume depletion.
Chronic Lung Disease (high)
Chronic CO2 retention → kidneys compensate by retaining bicarbonate.
What You Can Do
If low: calculate anion gap = Na - (Cl + HCO3)
Impact: High AG: DKA, lactic acidosis, toxins, renal failure. Normal AG: diarrhea, RTA. \u00B7 Timeline: Immediately
If high: assess volume status and medication list
Impact: Most metabolic alkalosis is from vomiting or diuretics \u00B7 Timeline: Immediately
If lifestyle changes aren't enough:
If anion gap elevated: check lactate, ketones, renal function, toxicology
Impact: Identifies specific cause of high-AG acidosis \u00B7 Timeline: Urgent
Recommended retest: q4-6h during acute acidosis management; per clinical context
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