Sleep Tools
Sleep Study Results Explainer
Enter the numbers from your sleep study report and get a plain-English breakdown of what they actually mean.
Enter your numbers
AHI is required. Oxygen nadir and sleep efficiency are optional but add more detail to your results.
Total breathing events per hour of sleep
The lowest blood oxygen saturation recorded during your study
Percentage of time in bed you were actually asleep
Your results explained
Enter your AHI to see a plain-English explanation of your results.
Frequently Asked Questions
Common questions about reading a sleep study report.
Sleep Medicine Basics
Types of Sleep Studies
Not all sleep studies are the same. Understanding the differences helps you know what to expect and why one type may have been ordered for you.
In-Lab
Polysomnography (PSG)
The gold standard sleep study. Conducted at a sleep center with a technologist applying 20+ sensors to monitor brain waves (EEG), eye movements (EOG), muscle activity (EMG), heart rhythm (ECG), breathing effort, airflow, blood oxygen, leg movements, and snoring. The most comprehensive diagnostic tool for all sleep disorders.
Cost: $1,000–$3,500
At-Home
Home Sleep Apnea Test (HSAT)
A portable device worn in your own bed. Monitors airflow, breathing effort, blood oxygen (SpO₂), and heart rate using 4–7 channels. Appropriate when moderate-to-severe OSA is strongly suspected in otherwise healthy adults. More convenient and significantly lower cost than in-lab studies.
Cost: $150–$400
Follow-Up
CPAP Titration Study
An in-lab study to calibrate your CPAP pressure after an OSA diagnosis. A technologist adjusts the pressure in real time as you sleep until the optimal therapeutic level is found. Often combined with a diagnostic PSG in a single "split-night study" to reduce total nights in the lab.
Often bundled with PSG
| Feature | PSG (In-Lab) | HSAT (At-Home) |
|---|---|---|
| Monitored channels | 20+ | 4–7 |
| Sleep staging | Yes (EEG) | No |
| Best for | Complex cases, children, suspected non-OSA disorders | Suspected moderate-severe OSA in adults |
| Cost | $1,000–$3,500 | $150–$400 |
| Setup | Sleep center technician | Self-applied at home |
Reading Your Report
Key Sleep Study Metrics Explained
Sleep study reports contain several metrics beyond just AHI. Here is what each one measures and why it matters clinically.
Primary Metric
AHI: Apnea-Hypopnea Index
Total breathing events (apneas + hypopneas) per hour of sleep. The primary diagnostic metric for OSA severity.
<5: Normal
5–14: Mild OSA
15–29: Moderate OSA
30+: Severe OSA
Oxygen
SpO₂ Nadir
The lowest blood oxygen saturation recorded during the night. Reflects how severely breathing events deprive the body of oxygen.
≥95%: Normal
90–94%: Mild desaturation
85–89%: Moderate desaturation
<85%: Severe (treatment urgent)
Sleep Quality
Sleep Efficiency
Time asleep divided by time in bed, expressed as a percentage. Reflects how consolidated and restorative your sleep is.
≥85%: Healthy
75–84%: Below ideal
<75%: Fragmented sleep
Arousal
Arousal Index
Number of partial awakenings per hour of sleep. Even brief arousals (3–15 seconds) disrupt sleep architecture without you fully waking up.
<15/hr: Within normal range
≥15/hr: Clinically elevated
REM Sleep
REM Latency
Time from sleep onset to the first REM sleep episode. Shortened REM latency (under 70 minutes) can indicate depression, narcolepsy, or REM sleep behavior disorder.
70–120 min: Typical
<70 min: Evaluate further
Architecture
Sleep Architecture
The breakdown of sleep stages: N1 (light), N2 (baseline), N3 (deep/restorative), and REM. OSA commonly reduces both REM and N3 (deep) sleep, leading to non-refreshing rest.
N3 (deep): typically 15–25%
REM: typically 20–25%
Preparation Guide
How to Prepare for a Sleep Study
Good preparation improves data quality and reduces the chance of a repeat study. Follow these steps for the most accurate results.
The Day Before
- Avoid caffeine after noon, as it delays sleep onset and reduces deep sleep
- No alcohol, as it distorts sleep architecture even if it helps you fall asleep
- Take your normal medications unless your physician says otherwise
- Wash your hair and leave it free of products, as gels and sprays interfere with EEG electrode adhesion
- Arrive in comfortable sleepwear you would actually sleep in
What to Bring
- Insurance card and photo ID
- Any current medications in their original labeled bottles
- A pillow from home if you prefer your own
- A book, phone, or light entertainment for the pre-sleep period
- A CPAP machine and mask if you already use one
During an In-Lab Study
- A technologist will apply sensors using water-soluble paste or gel, which is painless and removable
- You'll sleep in a private room that resembles a hotel more than a hospital
- Bathroom use is possible during the night. The technologist disconnects you temporarily
- The technologist monitors you remotely through the night and will not disturb you unless necessary
For Home Sleep Tests
- Follow the device instructions exactly. Incorrect placement is the most common source of error
- Sleep in your normal position and environment for representative data
- Place the device on your nightstand before starting so it is easy to reach
- Avoid napping the day of the test. Natural sleep pressure improves data quality
Clinical Guidance
Understanding Your Results: Next Steps by Severity
AHI severity guides treatment decisions. Here is what each category typically means for next steps. Always discuss specifics with your sleep physician.
| AHI Range | Diagnosis | Typical Next Steps |
|---|---|---|
| <5 | No OSA | Explore other causes of symptoms: insomnia, narcolepsy, thyroid dysfunction, or circadian rhythm disorder |
| 5–14 | Mild OSA | Lifestyle changes (weight management, positional therapy, reduce alcohol); consider CPAP if symptomatic |
| 15–29 | Moderate OSA | CPAP therapy recommended; oral appliance (mandibular advancement device) as an alternative for some patients |
| 30+ | Severe OSA | CPAP strongly recommended; prompt follow-up with sleep physician; evaluate cardiovascular and metabolic risk |
Summary
Key Takeaways
- Home sleep tests are appropriate for most adults suspected of moderate-to-severe OSA, with no overnight lab stay required.
- AHI is the primary diagnostic metric; SpO₂ nadir and sleep efficiency add important clinical context about severity and impact.
- Sleep efficiency below 75% often signals sleep fragmentation beyond just apnea, and warrants its own clinical discussion.
- An AHI of 15 or higher typically warrants treatment; even mild OSA (AHI 5–14) deserves evaluation if you are symptomatic.
- CPAP is the most effective treatment for moderate-to-severe OSA, reducing AHI by 80–90% when used consistently.
Sources
References
- 1. American Academy of Sleep Medicine. "Clinical Guideline for Diagnostic Testing for Adult Obstructive Sleep Apnea." 2017.
- 2. Berry RB, et al. "Rules for Scoring Respiratory Events in Sleep." Journal of Clinical Sleep Medicine. 2012.
- 3. Kapur VK, et al. "Clinical Practice Guideline for Diagnostic Testing for Adult Obstructive Sleep Apnea." Journal of Clinical Sleep Medicine. 2017.
- 4. Patil SP, et al. "Treatment of Adult Obstructive Sleep Apnea with PAP Therapy." Journal of Clinical Sleep Medicine. 2019.