EPO and sleep apnea syndrome: If such evidence is absent, as shown in Figure 3, and if the patient is asymptomatic, the Hct is less than 55%, [47]; pulse oximetry reveals an arterial oxygen saturation of ≥93%; there is no history of sleep apnea, tobacco, androgen, or diuretic use; and a serum erythropoietin assay is normal, the patient can be observed for a month and the Hct repeated.