The possibility of central sleep apnea (CSA) in any patient being prescribed autoCPAP is a concern. In our center, for patients with clinical conditions predisposing to CSA (eg, heart failure), autoCPAP is routinely avoided in favor of PSG. Occasionally, patients without significant comorbidities who are diagnosed with OSA by PSG or level 3 test and prescribed autoCPAP experience CSA on treatment related to high loop gain. Identification of such patients prior to starting CPAP is currently impossible, regardless of the diagnostic test used. Hence, we would argue that such a patient receiving a diagnosis of OSA by the elbow sign and prescribed autoCPAP would be identified by the high residual apnea-hypopnea index and referred for a more definitive assessment of CSA by PSG. Furthermore, one could argue that such an algorithm would save patients time and inconvenience and reduce costs to the system by reserving PSG for such selected cases.