If you’re a few weeks into CPAP therapy and staring at a screen full of unfamiliar numbers and charts — AHI, leak rate, pressure graphs — you’re not alone. Free tools like OSCAR (Open-Source CPAP Analysis Reporter) have made it much easier for people to see their own therapy data, but that data can be genuinely confusing without some context. Here’s a general primer on what the most common metrics mean.
AHI: the headline number
AHI stands for Apnea-Hypopnea Index — the average number of breathing pauses (apneas) or partial obstructions (hypopneas) you experience per hour of sleep. According to the American Academy of Sleep Medicine, an AHI under 5 is generally considered within the normal range, 5–15 is classified as mild sleep apnea, 15–30 as moderate, and above 30 as severe. On CPAP therapy, the goal is typically to bring your treated AHI down close to that under-5 range, though what counts as “well controlled” can vary by individual and should be interpreted by your sleep physician, not by a general benchmark alone.
Leak rate
Leak rate measures how much air is escaping around your mask seal rather than going where it’s supposed to. Some leak is normal and built into every mask’s design (called “intentional” or “vent” leak), but excess “unintentional” leak — from a poor mask fit, mouth breathing with a nasal mask, or a worn-out cushion — can throw off other readings and reduce how effectively therapy is working. The Sleep Foundation notes that persistent high leak is one of the most common reasons people feel like CPAP “isn’t working” even when their machine is functioning correctly.
RERAs and flow limitations
Some data platforms also flag Respiratory Effort-Related Arousals (RERAs) and flow limitations — subtler breathing disruptions that don’t fully qualify as an apnea or hypopnea but can still fragment sleep. These are harder to interpret without clinical training, since not every consumer device or software captures them identically. If you’re consistently seeing a lot of flagged events despite a normal AHI, that pattern is worth bringing to a sleep specialist rather than trying to self-diagnose from the data alone.
Pressure settings
Auto-adjusting (“APAP”) machines vary pressure within a prescribed range based on what they detect in real time. Consistently running near the top of your pressure range can be a sign that your prescribed range may need to be reassessed — but pressure changes should be made in coordination with your prescribing physician or durable medical equipment (DME) provider, not through self-adjustment, since incorrect settings can create new problems like increased leak or central apnea events.
The most important takeaway
Tools like OSCAR are genuinely useful for spotting patterns and having a more informed conversation with your care team, and many people find real value in tracking their own trends over time. But according to both the Johns Hopkins Medicine and Sleep Foundation guidance on CPAP therapy, data interpretation and any changes to your prescribed treatment should ultimately go through your sleep physician, who has your full clinical picture — the raw numbers alone don’t tell the whole story.
This article is for general educational purposes only and is not a substitute for professional medical advice. If you have questions about your CPAP therapy or sleep study results, please consult your sleep physician or DME provider.
— Gemifys
