What is Standard Bicarbonate (B-)?
Standard bicarbonate is a biomarker used to assess the body's acid-base balance, especially the metabolic component. Bicarbonate (HCO₃⁻) is one of the most important buffering substances in the blood and plays a central role in maintaining a stable pH level by neutralizing hydrogen ions.
Standard bicarbonate differs from the actual bicarbonate value (P-HCO₃⁻) in plasma because it is a calculated value that indicates the bicarbonate concentration under standardized conditions. This means that it is calculated at an arterial pCO₂ value of 5.3 kPa (40 mmHg) and temperature of 37°C, regardless of the patient's current respiratory status. This makes it particularly useful for isolating the metabolic component of acid-base balance and minimizing respiratory interference.
How is Standard Bicarbonate used in healthcare?
Standard Bicarbonate is an important part of a blood gas analysis and is used to:
- Assess acid-base status: Helps identify metabolic disorders such as acidosis or alkalosis.
- Differentiate between respiratory and metabolic disorders: Since standard bicarbonate is independent of respiratory effects, it can more clearly show whether a disorder is metabolic in nature.
- Monitor patients with chronic diseases: For example, in chronic kidney disease, diabetic ketoacidosis, lung diseases and electrolyte disorders.
- Evaluate kidney function: The kidney is an important regulator of acid-base balance and a change in standard bicarbonate can indicate kidney involvement.
Why is the analysis performed?
A standard bicarbonate sample is performed if there is a suspicion of:
Metabolic acidosis occurs when the pH is too low due to decreased bicarbonate levels
- Diabetic ketoacidosis
- Lactic acidosis
- Renal failure
- Poisonings (e.g. methanol, ethylene glycol, salicylates)
- Severe diarrhea or renal loss of bicarbonate
Metabolic alkalosis occurs when the pH is too high due to increased bicarbonate levels
- Severe vomiting
- Diuretics (such as loop or thiazide diuretics)
- Hyperaldosteronism
- Bicarbonate intoxication
Interpretation of test results for P-standard bicarbonate
The reference range for standard bicarbonate is 22 - 27 mmol/L. Values outside this range indicate an acid-base disorder:
| Value (mmol/L) | Interpretation | Possible causes |
|---|---|---|
| < 22 mmol/L | Metabolic acidosis | Diabetic ketoacidosis, renal failure, lactic acidosis, intoxications, diarrhea |
| > 27 mmol/L | Metabolic alkalosis | Vomiting, diuretics, hyperaldosteronism, excessive bicarbonate administration |
In case of deviating values, the analysis should always be interpreted together with other blood gas parameters (e.g. pH, pCO₂ and anion gap) to understand the underlying cause of the acid-base disturbance.