When a doctor says “sleep study,” it can mean any one of four quite different tests. The simplest difference between them: how much of your body they measure while you sleep, and whether a trained technologist is watching over the night.
Sleep tests are grouped into Levels 1 to 4 (some doctors use the word “Type” instead of “Level” — they mean the same thing). The idea is straightforward: a Level 1 study records many signals under supervision, and each step down records fewer signals with less oversight.
The most complete test. It records brain waves (to show if and when you are truly asleep, and in which stage), eye and chin-muscle movement, heart rhythm, airflow, breathing effort at the chest and abdomen, blood-oxygen level, body position, and leg movements. A technologist stays with you through the night and can re-attach a sensor that slips. Because it measures your actual sleep, it can diagnose not only sleep apnea but many other sleep disorders.
Records the same wide set of signals as Level 1, including brain waves — but with no technologist present. If a sensor comes loose in the night, there is no one there to fix it, so parts of the recording can be lost.
A limited test built to look for one thing: obstructive sleep apnea. It typically records airflow, breathing effort, oxygen level, and heart rate. It does not record brain waves, so it cannot tell when you are actually asleep, and it cannot detect most other sleep disorders. This is the test most people mean by an “at-home sleep test.”
Records only one or two signals, most often blood-oxygen level (and sometimes airflow or heart rate). It is the least detailed option and gives the narrowest picture of your night.
| Capability | Level 1In-lab, attended | Level 2Full, unattended | Level 3Home apnea test | Level 41–2 signals |
|---|---|---|---|---|
| Records brain waves / measures real sleep | Yes | Yes | No | No |
| Technologist present overnight | Yes | No | No | No |
| Measures breathing & blood oxygen | Yes | Yes | Yes | Limited |
| Can diagnose obstructive sleep apnea | Yes | Yes | Yes* | Screen only |
| Can find other sleep disorders | Yes | Yes | No | No |
| Typical number of signals | 12+ | 7+ | 4–7 | 1–2 |
| Usual setting | Sleep lab | Home | Home | Home |
Yes = does this well · Limited / Screen only = partial ·
No = cannot do this.
*A home apnea test can confirm apnea when it is clearly present, but a normal result does not
rule it out — see “When ‘normal’ isn’t normal.”
The fewer the signals, the more a test can miss. Levels 3 and 4 are screening tools for obstructive sleep apnea in people who are already likely to have it — not a complete picture of your sleep. A full Level 1 study remains the reference standard against which all the others are measured.
Which level suits you depends on your symptoms and your general health. The next guide explains what a home test can miss and who it was never designed for.
Wondering which level of study is right for you? Our team is happy to help.