Normal Bicarbonate (HCO3) Levels
The normal serum bicarbonate range is 22-26 mmol/L, though some evidence supports a slightly broader range of 23-30 mmol/L to avoid missing subtle acid-base disorders. 1
Standard Reference Range
The typical normal serum bicarbonate range is 22-26 mmol/L, as consistently referenced across multiple clinical guidelines and the FDA drug label for intravenous bicarbonate. 1, 2
The FDA states that bicarbonate is a normal constituent of body fluids with normal plasma levels ranging from 24 to 31 mEq/L, representing a slightly broader upper limit than the traditional range. 2
More recent evidence suggests considering 23-30 mmol/L as the normal range to improve sensitivity for detecting acid-base disorders, though this represents a shift from traditional teaching. 1
Clinical Context for Interpretation
Serum bicarbonate below 22 mmol/L almost always indicates metabolic acidosis and warrants further evaluation, particularly in patients with chronic kidney disease where monthly monitoring is recommended. 1, 3
Bicarbonate levels above 27 mmol/L may indicate either metabolic alkalosis or compensatory retention in chronic respiratory acidosis, requiring arterial blood gas analysis to differentiate between primary and compensatory processes. 4, 1
Important Clinical Considerations
In chronic kidney disease patients, maintaining serum bicarbonate at or above 22 mmol/L is recommended to prevent complications including protein catabolism, bone disease, and CKD progression. 4, 1, 3
Research suggests that higher bicarbonate levels within the normal range (approaching 28-30 mmol/L) may be associated with better renal outcomes and reduced CKD progression, though this remains an area of ongoing investigation. 5, 6
The kidneys regulate plasma bicarbonate concentration through urinary acidification when there is a deficit or alkalinization when there is an excess, with less than 1% of filtered bicarbonate normally excreted in urine in healthy adults. 2
Common Pitfalls to Avoid
Do not assume that bicarbonate levels in the low-normal range (22-23 mmol/L) are adequate for all patients—in CKD patients specifically, targeting higher levels within the normal range may provide additional benefit. 5, 6, 7
Remember that the "CO2" measurement on a basic metabolic panel reflects total carbon dioxide content (predominantly bicarbonate), not arterial PCO2, which can lead to confusion when interpreting results. 1
In obese patients with sleep-disordered breathing, a bicarbonate level above 27 mmol/L should prompt evaluation for obesity hypoventilation syndrome, as this represents a clinically significant threshold for further testing. 4