Increased blood glycohemoglobin A1c levels lead to overestimation of arterial oxygen saturation by pulse oximetry in patients with type 2 diabetes

BACKGROUND: Non-enzymatic glycation increases hemoglobin-oxygen affinity and reduces oxygen delivery to tissues by altering the structure and function of hemoglobin. OBJECTIVES: We investigated whether an elevated blood concentration of glycosylated hemoglobin (HbA1c) could induce falsely high pulse oximeter oxygen saturation (SpO(2)) in type 2 diabetic patients during mechanical ventilation or oxygen therapy. METHODS: Arterial oxygen saturation (SaO(2)) and partial pressure of oxygen (PO(2)) were determined with simultaneous monitoring of SpO(2) in 261 type 2 diabetic patients during ventilation or oxygen inhalation. RESULTS: Blood concentration of HbA1c was >7% in 114 patients and ≤ 7% in 147 patients. Both SaO(2) (96.2 ± 2.9%, 95% confidence interval [CI] 95.7-96.7% vs. 95.1 ± 2.8%, 95% CI 94.7-95.6%) and SpO(2) (98.0 ± 2.6%, 95% CI 97.6-98.5% vs. 95.3 ± 2.8%, 95% CI 94.9-95.8%) were significantly higher in patients with HbA1c >7% than in those with HbA1c ≤ 7% (Data are mean ± SD, all p < 0.01), but PO(2) did not significantly differ between the two groups. Bland-Altman analysis demonstrated a significant bias between SpO(2) and SaO(2) (1.83 ±0.55%, 95% CI 1.73% -1.94%) and limits of agreement (0.76% and 2.92%) in patients with HbA1c >7%. The differences between SpO(2) and SaO(2) correlated closely with blood HbA1c levels (Pearson’s r = 0.307, p < 0.01). CONCLUSIONS: Elevated blood HbA1c levels lead to an overestimation of SaO(2) by SpO(2), suggesting that arterial blood gas analysis may be needed for type 2 diabetic patients with poor glycemic control during the treatment of hypoxemia.