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Electrolytes
Bicarbonate (total CO2) (HCO3-)
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This is the date the draft was written, not a medical review date.
Serum bicarbonate (usually reported as total CO2) is the main buffer base of extracellular fluid and a first screen for metabolic acid-base disorders.
Reference interval
| Conventional (mEq/L) | SI (mmol/L) | |
|---|---|---|
| Adults | 23–29 mEq/L | 23–29 mmol/L |
Specimen: Serum or plasma · Conventional × 1 = SI
Causes of high values
Metabolic alkalosis (vomiting, diuretics, mineralocorticoid excess, alkali ingestion) and compensated chronic respiratory acidosis.
Causes of low values
Metabolic acidosis (ketoacidosis, lactic acidosis, uraemia, toxic ingestions, diarrhoea, renal tubular acidosis) and compensated respiratory alkalosis.
Pre-analytical and method notes
Venous total CO2 is typically a few mmol/L higher than the calculated arterial bicarbonate of a blood gas (22-26 mmol/L), and values fall if the tube is left uncapped or underfilled. Reference limits vary by method and laboratory.
Related calculators
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)
- Brenner and Rector's The Kidney. Elsevier, 11th edition (2019) — Tier 3 (textbook)
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