Figure 3. Receiver operating characteristic (ROC) curve analysis for detecting low bicarbonate (bicarbonate ion [HCO₃⁻] < 24 mmol/L) and high bicarbonate (HCO₃⁻ ≥ 24 mmol/L).

(A) The ROC curve of serum total carbon dioxide (CO₂) for low bicarbonate. (B) The ROC curve of serum total CO₂ for high bicarbonate. (C) The ROC curve of approximated HCO₃⁻ concentration for low bicarbonate. (D) The ROC curve of approximated HCO₃⁻ concentration for high bicarbonate.

AUC, area under the curve.