What is the normal range for bicarbonate (HCO3) in arterial blood?

• A. 18-22 mEq/L
• B. 22-26 mEq/L
• C. 28-32 mEq/L
• D. 34-38 mEq/L

Answer: (B)

Arterial bicarbonate (HCO3) reflects the metabolic component of acid-base balance and is tightly regulated by the kidneys as part of the buffering system. The normal range is about 22 to 26 mEq/L. Values within this range help keep the blood pH within its normal range through renal production and reabsorption of bicarbonate. If HCO3 falls below 22, it points to metabolic acidosis (loss of base or gain of hydrogen ions). If HCO3 rises above 26, it indicates metabolic alkalosis (gain of base or loss of hydrogen ions). In practice, clinicians look at HCO3 alongside the other ABG values (pH and PaCO2) to determine the acid-base status and whether there is primary metabolic or respiratory disturbance and whether compensation is appropriate.