From the Guidelines
A slightly low bicarbonate level in an otherwise normal Comprehensive Metabolic Panel suggests mild metabolic acidosis, which may not require immediate intervention if the patient is asymptomatic.
Clinical Significance
The clinical significance of a slightly low bicarbonate (HCO3) level can be understood by considering the body's acid-base balance. Bicarbonate levels reflect the kidneys' ability to compensate for acid production by retaining bicarbonate. A slightly low level may indicate either excess acid production or inadequate renal compensation.
Normal Bicarbonate Range and Monitoring
Normal bicarbonate ranges from 22-29 mEq/L, so values just below 22 mEq/L warrant monitoring rather than aggressive treatment 1.
Investigating the Cause
The cause should be investigated through clinical history, focusing on potential sources like diarrhea, early kidney dysfunction, medication effects (particularly metformin or carbonic anhydrase inhibitors), uncontrolled diabetes, or excessive exercise.
Treatment Approach
For mild decreases (19-21 mEq/L), no specific treatment is typically needed beyond addressing the underlying cause. Patients should maintain adequate hydration and may benefit from reducing high-protein diets if chronically low. More significant decreases (<18 mEq/L) or the presence of symptoms like fatigue, rapid breathing, or confusion would necessitate more urgent evaluation.
Recent Guidelines
Recent guidelines suggest that in people with CKD and serum bicarbonate concentrations <22 mmol/l, treatment with oral bicarbonate supplementation be given to maintain serum bicarbonate within the normal range, unless contraindicated 1. However, the most recent study from 2019 provides conditional recommendations for using serum bicarbonate levels to decide when to measure PaCO2 in patients with sleep-disordered breathing, suggesting a threshold of 27 mmol/L 1.
Recommendation
Based on the most recent and highest quality study, for patients with a slightly low bicarbonate level and no symptoms, monitoring and addressing the underlying cause is recommended, rather than immediate intervention.
From the Research
Clinical Significance of Slightly Low Bicarbonate in CMP
- A slightly low bicarbonate level in an otherwise normal Comprehensive Metabolic Panel (CMP) may have clinical significance, particularly in patients with chronic kidney disease (CKD) 2, 3.
- Studies have shown that lower serum bicarbonate levels are associated with an increased risk of kidney disease progression and acute kidney injury (AKI) 2, 3.
- A high serum bicarbonate level within the normal range may be effective for preventing CKD progression, as it is independently associated with a low risk of CKD progression 2.
- Oral sodium bicarbonate supplementation has been shown to improve parameters of metabolic acidosis and serum nutritional markers in non-dialysed CKD patients, although its effect on blood pressure and vascular stiffness is unclear 4.
- The association between serum bicarbonate level and the risk of AKI has been demonstrated, with a bicarbonate level ≤24 mEq/L being associated with a significantly increased risk of AKI compared to those with a bicarbonate level of 25-28 mEq/L 3.
- Treatment of metabolic acidosis with sodium bicarbonate may slow the decline rate of kidney function and potentially improve vascular endothelial function in patients with CKD 5.
Key Findings
- A 1 mEq/l increase in serum bicarbonate level is associated with a low risk of CKD progression 2.
- Patients with the lowest quartile of serum bicarbonate levels have a high risk of CKD progression compared to patients with high serum bicarbonate levels 2.
- Oral sodium bicarbonate supplementation increases serum bicarbonate level and slows the decline in estimated glomerular filtration rate (eGFR) in CKD patients 5.
- Lower serum bicarbonate levels are an independent risk factor for the development of AKI 3.