CO2 (Bicarbonate) — Normal Range & Interpretation

Clinical Context

Serum CO2 on the BMP measures bicarbonate, the primary extracellular buffer maintaining acid-base balance. It reflects the metabolic component of the Henderson-Hasselbalch equation and works opposite PaCO2 in arterial blood gas interpretation. Bicarbonate guides clinicians in identifying metabolic acidosis and alkalosis, calculating the anion gap, and evaluating respiratory compensation in chronic pulmonary disease.

Low bicarbonate signals metabolic acidosis from diabetic ketoacidosis, lactic acidosis, chronic kidney disease, severe diarrhea, renal tubular acidosis, or toxic ingestions such as methanol, ethylene glycol, and salicylates. Elevated bicarbonate indicates metabolic alkalosis, classically from vomiting, nasogastric suction, diuretic use, hypokalemia, hyperaldosteronism, or chronic respiratory acidosis with renal compensation in COPD patients.

Board-style questions on bicarbonate pair changes in the value with clinical scenarios and distinguish primary metabolic disorders from compensatory shifts. Expect questions linking low CO2 to anion gap acidosis in DKA, pairing elevated CO2 with loop diuretic therapy or persistent emesis, and recognizing chronic CO2 elevation as renal compensation in long-standing COPD. Candidates also encounter questions tying bicarbonate trends to potassium shifts, expected respiratory compensation using Winter's formula, and medication effects from acetazolamide, spironolactone, and sodium bicarbonate therapy in primary care management.

Practice Questions

Related Labs

• Sodium (Na) — mEq/L
• Potassium (K) — mEq/L
• Chloride (Cl) — mEq/L
• BUN — mg/dL
• Creatinine — mg/dL

Sources

• MedlinePlus