What Is CO2 / Bicarbonate? Normal vs Optimal Range Explained

Your body constantly produces acid as a byproduct of metabolism—carbonic acid from CO2 production, lactic acid from anaerobic exercise, ketoacids from fat burning, and organic acids from protein metabolism. Bicarbonate neutralizes this acid load, and your kidneys regenerate the consumed bicarbonate to maintain the buffer. The CTD maps over 890 compound interactions with bicarbonate transport and acid-base regulation genes, demonstrating how many medications and metabolic states influence this critical buffer system. A bicarbonate of 21 mmol/L—just 1 point below the lab lower limit—already indicates meaningful acid accumulation that is overwhelming the body's buffering capacity. In chronic kidney disease, bicarbonate below 22 mmol/L accelerates kidney function decline by 1–2 mL/min/year and promotes muscle protein breakdown.

PubMed indexes over 32,000 clinical publications on serum bicarbonate and acid-base physiology. The clinical value of bicarbonate lies in its integration with other metabolic panel values—specifically sodium and chloride—to calculate the anion gap: sodium minus (chloride plus bicarbonate). A normal anion gap (8–12) with low bicarbonate points to bicarbonate loss from diarrhea, renal tubular acidosis, or saline administration. An elevated anion gap (above 12) with low bicarbonate indicates unmeasured acids are accumulating—ketoacids in DKA, lactic acid in sepsis or shock, or toxic alcohols (methanol, ethylene glycol). The mnemonic MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates) captures the major causes.

High bicarbonate (metabolic alkalosis) most commonly results from volume and chloride depletion—the classic scenario is a patient on chronic diuretics or one who has been vomiting. The body loses hydrogen and chloride ions, and the kidneys compensate by retaining bicarbonate. In the ICU, excessive nasogastric suction and overzealous IV bicarbonate administration are additional culprits. Metabolic alkalosis above 35 mmol/L can cause cardiac arrhythmias, reduced oxygen delivery to tissues (alkalotic leftward shift of the hemoglobin-oxygen dissociation curve), and neuromuscular irritability. For patients with chronic kidney disease, oral sodium bicarbonate supplementation (targeting serum bicarbonate of 22–26 mmol/L) has been shown to slow kidney function decline and preserve lean muscle mass.