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Blood gases
Arterial bicarbonate (HCO3-)
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The main extracellular buffer and the metabolic component of acid-base balance, regulated by the kidney. The value on a blood gas report is calculated from pH and PaCO2 using the Henderson-Hasselbalch equation.
Reference interval
| Conventional (mEq/L) | SI (mmol/L) | |
|---|---|---|
| Adults | 22–26 mEq/L | 22–26 mmol/L |
Specimen: Arterial whole blood (calculated from pH and PaCO2) · Conventional × 1 = SI
Causes of high values
Metabolic alkalosis (vomiting, nasogastric loss, diuretics, mineralocorticoid excess, alkali ingestion) and renal compensation for chronic respiratory acidosis.
Causes of low values
Metabolic acidosis (ketoacidosis, lactic acidosis, renal failure, diarrhoea, renal tubular acidosis, toxic alcohols) and renal compensation for chronic respiratory alkalosis.
Pre-analytical and method notes
The arterial value is calculated and the serum total CO2 measured on a chemistry analyser is slightly higher (it includes dissolved CO2 and carbamino compounds). Expected compensation is approximate and compensation takes hours (respiratory) to days (renal). Reference intervals vary by laboratory, method and population; use the interval printed on the report.
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References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)
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