Bicarbonate (HCO3) is a vital electrolyte and a byproduct of the body’s metabolism. It acts as a chemical buffer, managed by the lungs and kidneys to maintain a stable blood pH.
A bicarbonate test (often part of a Metabolic Panel) is essential for diagnosing acid-base imbalances.
While specific reference ranges may vary slightly between diagnostic laboratories, the standard window is:
Normal Range: 22 to 28 mmol/L (millimoles per liter)
If your results fall outside this range, it typically indicates that your body is struggling to expel carbon dioxide or that your kidneys are struggling to manage metabolic waste.
A high concentration of bicarbonate in the blood suggests a shift toward alkalinity. This is often categorized into two primary physiological drivers:
1. Metabolic Alkalosis
This occurs when the body loses too much acid or gains too much base.
Severe Vomiting: Leads to the loss of stomach acid (hydrochloric acid).
Diuretic Use: Long-term use of “water pills” can cause the kidneys to excrete excess hydrogen.
Excessive Intake: Overuse of antacids or receiving specific IV fluids.
2. Compensatory Respiratory Acidosis
When the lungs cannot properly expel CO2 (due to COPD or respiratory failure), the kidneys retain bicarbonate to “offset” the acidity, raising the blood levels.
3. Endocrine Disorders
Conn’s Syndrome: Excess aldosterone leads to potassium loss and bicarbonate retention.
Cushing’s Syndrome: High cortisol levels can disrupt electrolyte balance.
Low bicarbonate levels indicate that the blood is becoming too acidic, or that the body is losing its buffering capacity.
1. Metabolic Acidosis
This is a serious condition where acid builds up in the body. Common causes include:
Diabetic Ketoacidosis (DKA): A life-threatening complication of diabetes.
Lactic Acidosis: Often caused by severe infection (sepsis) or heart failure.
Kidney Disease: AKI (Acute Kidney Injury) or CKD (Chronic Kidney Disease) prevents the kidneys from filtering acid.
Toxic Ingestion: Overdoses of salicylates (aspirin), ethylene glycol (antifreeze), or methanol.
2. Respiratory Alkalosis (Compensation)
During hyperventilation or acute anxiety, the body exhales too much CO2. The kidneys respond by flushing out bicarbonate to bring the pH back to a neutral state.
3. Gastrointestinal & Medication
Severe Diarrhoea: Unlike vomiting, diarrhea results in a significant loss of base (bicarbonate) from the lower GI tract.
Acetazolamide: A medication used for glaucoma or altitude sickness that forces the kidneys to excrete bicarbonate.
| Level Status | Technical Term | Common Potential Causes |
| High (>28 mmol/L) | Alkalosis | COPD, Chronic Vomiting, Conn’s Syndrome, Diuretics |
| Low (<22 mmol/L) | Acidosis | Kidney Failure, DKA, Severe Diarrhoea, Shock/Sepsis |
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