Normal Bicarbonate Range in Blood
The normal range for bicarbonate (HCO3-) in the blood is 22-29 mmol/L (or mEq/L). This range is supported by multiple clinical guidelines and is critical for maintaining proper acid-base balance in the body.
Understanding Bicarbonate and Acid-Base Balance
Bicarbonate serves as a key buffer in the blood, helping to maintain the body's pH within the normal range of 7.35-7.45. It works through the following mechanism:
CO2 + H2O ⟶ H2CO3 ⟶ H+ + HCO3-
This buffering system is essential for:
- Neutralizing excess acids produced by normal metabolism
- Preventing acidosis or alkalosis
- Supporting proper cellular function
Clinical Significance of Bicarbonate Levels
Low Bicarbonate (<22 mmol/L)
- Indicates metabolic acidosis 1
- May be seen in conditions such as:
- Chronic kidney disease
- Diabetic ketoacidosis 1
- Lactic acidosis
- Diarrhea (loss of bicarbonate)
High Bicarbonate (>29 mmol/L)
- Indicates metabolic alkalosis
- May be seen in:
- Chronic respiratory acidosis (compensated)
- Vomiting
- Excessive alkali intake
- Some diuretic therapies
Clinical Applications
Screening for Metabolic Disorders
- Bicarbonate levels <22 mmol/L warrant treatment in chronic kidney disease patients 1, 2
- Levels <27 mmol/L have a high negative predictive value (99.0%) for ruling out obesity hypoventilation syndrome 1
Treatment Thresholds
- In CKD patients, treatment with oral bicarbonate supplementation is recommended when serum bicarbonate is <22 mmol/L 1, 2
- The strongest evidence supports treatment when levels fall below 18 mmol/L in adults 2
Prognostic Value
- Both high (>27 mmol/L) and low (≤17 mmol/L) serum bicarbonate levels are associated with increased risk for mortality and hospitalization in dialysis patients 3
- In elderly patients with CKD, higher serum bicarbonate levels within the normal range are associated with lower risk of CKD progression 4
- In generally healthy older individuals, low serum bicarbonate (<23 mmol/L) is associated with higher mortality independent of systemic pH 5
Monitoring Considerations
Regular monitoring of bicarbonate levels is essential in patients with:
- Chronic kidney disease
- Respiratory disorders
- Diabetes
- Heart failure
- Patients on certain medications (diuretics, metformin)
In patients with CKD, maintaining bicarbonate within the normal range (≥22 mmol/L) is recommended 2
Pitfalls and Caveats
- Laboratory normal ranges may vary slightly between institutions
- Bicarbonate levels should be interpreted in the context of other acid-base parameters (pH, PaCO2)
- Venous bicarbonate measurements may differ slightly from arterial measurements
- Bicarbonate levels can be affected by respiratory status, as respiratory compensation can mask underlying metabolic disorders
- Treatment of low bicarbonate must be balanced against risks of fluid overload, especially in patients with heart failure or volume overload 2