What does the Carbon Dioxide (Bicarbonate), Serum test measure?

Why is Carbon Dioxide (Bicarbonate), Serum measured?

Serum total CO2 within the CMP provides the acid-base balance indicator. Low CO2 (<22 mEq/L) indicates metabolic acidosis — causes include diabetic ketoacidosis, lactic acidosis, renal tubular acidosis, diarrhoea, and advanced CKD — or respiratory alkalosis from hyperventilation. High CO2 (>29 mEq/L) indicates metabolic alkalosis — from vomiting, diuretic use, or hypokalaemia — or compensated respiratory acidosis. Combined with sodium and chloride, CO2 enables anion gap calculation. In CKD monitoring, falling bicarbonate signals progressive metabolic acidosis requiring bicarbonate supplementation per KDIGO guidelines.

Reference ranges

Standard reference

22–29 mEq/L (22–29 mmol/L) # REVIEWER FLAG: Confirm Quest Diagnostics reference range for total CO2 — values of 22–29 mEq/L are standard; some platforms use 20–31 mEq/L. The serum total CO2 measured in the CMP is 95–99% bicarbonate and 1–5% dissolved CO2 and carbonic acid — it approximates but does not equal arterial bicarbonate.

Functional medicine optimal

24–27 mEq/L (functional medicine optimal for normal physiological acid-base buffering without acidaemia or alkalaemia stress on enzyme function). # REVIEWER FLAG: Not standardised as a clinical guideline target — reviewer to confirm framing.

Units

mEq/L, mmol/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.