A residual AHI below five events per hour is a common reference point in PAP treatment, but it is not a universal pass-or-fail rule for a machine report. Your clinician interprets the value alongside symptoms, leak, how much of your sleep is treated and any other relevant measurements.
Aiming for zero at any cost is not the goal. Neither is dismissing continuing symptoms because the display shows a low number.
What the machine counts
Residual AHI is the device's estimate of apneas and hypopneas during recorded treatment. It usually relies on airflow and pressure signals, without the full measurements of a laboratory sleep study. Awake breathing, leak and device-specific detection can affect the result.
A low number after only part of the night on treatment says little about the sleep that followed without the mask. It also does not directly measure oxygen levels, carbon dioxide, total sleep quality or daytime alertness.
Read a pattern, not a single score
One unusual night can occur around congestion, a disturbed night, a changed sleeping position or a fitting problem. Look for a sustained change using a comparable reporting period on the same device.
If the number remains higher than the target agreed with your clinician, or rises unexpectedly, bring the report for review. An event-type breakdown can help guide questions, but a clear-airway label does not independently diagnose central apnea.
Do not raise pressure simply because the total AHI increased. The response to a leak problem differs from the response to another type of breathing disturbance.
Symptoms still count
If you feel better, use PAP throughout sleep and have reassuring treatment data, the overall picture may support continuing the plan. If you remain very sleepy or unwell, a low AHI should not end the investigation.
The team may consider mask-related awakenings, insufficient sleep, other sleep disorders, medicines or medical conditions as well as residual breathing problems. Further testing is sometimes useful, but not everyone doing well needs a repeat sleep study.
For a review, bring the dates, usage, leak and event trend plus a brief account of your sleep and daytime symptoms. That is more useful than asking whether one isolated number is good or bad.
Related reading: Still tired on CPAP despite a low AHI?
Sources and further reading
ATS statement on PAP adherence tracking