Normal and elevated HbA1C levels correlate with severity of hypoxemia in patients with obstructive sleep apnea and decrease following CPAP treatment.

PURPOSE: Sleep apnea is associated with higher HbA1C levels in patients with and without diabetes but whether its severity correlates with HbA1C levels ranging from normal to abnormal is less clear. Also, the effect of continuous positive airway pressure (CPAP) treatment on HbA1C levels in patients with sleep apnea is controversial.

METHODS: Thirty consecutive patients with obstructive sleep apnea were studied. None of the patients was previously diagnosed with diabetes. All patients underwent overnight polysomnography and HbA1C levels were determined. Patients were subdivided into three groups according to their HbA1C levels: <6% (n = 10), 6-6.5% (n = 10), and ≥6.5% (n = 10). Polysomnography and determination of HbA1C level were repeated in patients with severe sleep apnea (n = 12) following 3-5 months of CPAP treatment.

RESULTS: HbA1C levels across the spectrum from normal to abnormal correlated with severity of hypoxemia (average SpO(2), r = -0.43, p = 0.019 and percent time with SpO(2) < 90%, r = 0.48, p = 0.007). HbA1C levels decreased from a mean of 6.47 ± 0.67% to a mean of 6.28 ± 0.51%, p = 0.038 in 12 patients with severe sleep apnea following 3-5 months of CPAP treatment.

CONCLUSIONS: The severity of hypoxemia in patients with sleep apnea correlates with HbA1C levels ranging from normal to pre-diabetes and diabetes. CPAP treatment for 3-5 months decreases HbA1C levels in patients with severe sleep apnea.