Serum CO2 in Diabetic Ketoacidosis
Serum CO2 (bicarbonate) is LOW in diabetic ketoacidosis (DKA), serving as one of the core diagnostic criteria for this condition.
Diagnostic Criteria and CO2 Levels
The American Diabetes Association establishes that **bicarbonate <15 mEq/L is a diagnostic criterion for DKA**, along with blood glucose >250 mg/dL and arterial pH <7.3 1. The severity of DKA can be stratified based on bicarbonate levels:
- Mild DKA: Bicarbonate 10-15 mEq/L 2
- Moderate DKA: Bicarbonate <10 mEq/L 2
- Severe DKA: Bicarbonate significantly <10 mEq/L 2
Pathophysiology of Low Bicarbonate
The low serum CO2/bicarbonate in DKA results from the metabolic acidosis caused by accumulation of ketoacids (primarily beta-hydroxybutyrate and acetoacetate) 2. This creates a high anion gap metabolic acidosis, with anion gap >10 mEq/L in mild cases and >12 mEq/L in moderate to severe cases 2.
Clinical Monitoring
Resolution of DKA requires serum bicarbonate ≥18 mEq/L (along with glucose <200 mg/dL and venous pH >7.3) 1. During treatment, venous pH and anion gap should be monitored every 2-4 hours to track resolution of acidosis 1.
Important Caveats
- In starvation ketosis (a differential diagnosis), serum bicarbonate is usually not lower than 18 mEq/L, helping distinguish it from DKA 1
- The low bicarbonate correlates with the elevated anion gap, with the relationship approximating: change in total CO2 = 0.74 + 1.00 × change in anion gap 3
- Bicarbonate therapy is only considered when pH <6.9, and is not necessary if pH >7.0 1