By REM Manager

Sleep studies generate a large quantity of information regarding a patient’s sleep quality. Patients and physicians only view a fraction of this data, but it is important to analyze the proper metrics. While in-lab testing is more comprehensive, home sleep tests generally focus on a few categories and are typically used to diagnose sleep apnea severity. Sleep efficiency, arousals, apnea-hypopnea index (AHI), and oxygen desaturation index (ODI) are four critical metrics for sleep centers to track. Understanding how to evaluate these components can increase sleep study success and patient satisfaction.

Sleep Efficiency

Sleep efficiency is an important parameter that calculates the percentage of time in bed spent sleeping. This ratio between total sleep time and total recording time is helpful for a physician to evaluate sleep conditions and recommend the proper course of action. Patients with difficulties initiating or maintaining sleep have diminished sleep efficiency. This can have an adverse effect on the patient’s health and is typically linked to various conditions, such as depression. On the contrary, falling asleep right away indicates sleep deprivation and possibly a disorder.


Arousals are brief interruptions of sleep lasting anywhere from three to 15 seconds. Patients are usually not aware of arousals, but they can cause tiredness for people who are more sensitive to sleep disruptions. As little as five arousals per hour can make some people feel chronically sleepy. Physicians are able to better understand the severity by tracking how many times a patient’s sleep was disrupted. Arousals are registered in the sleep study and reported both as a total number and a frequency per hour. A patient is more likely to feel tired if the arousal index is higher.

Apnea-Hypopnea Index

AHI is a scale that determines whether a patient has sleep apnea, a stoppage in breathing for 10 seconds or more while asleep. It is also useful in measuring the severity of sleep apnea. AHI calculates how often a patient has apnea or hypopnea during one night and divides this number by the total hours of sleep.

  • Normal sleep: AHI of fewer than 5 events per hour
  • Mild sleep apnea: AHI of 5 to 14 events per hour
  • Moderate sleep apnea: AHI of 15 to 29 events per hour
  • Severe sleep apnea: AHI of 30 or more events per hour

Physicians typically recommend a CPAP machine for patients with moderate or severe sleep apnea. Lifestyle changes such as losing weight, exercising, and quitting smoking are also beneficial.

Oxygen Desaturation Index

ODI is another valuable metric in sleep studies. This determines how often a patient’s blood oxygen level drops below a certain value per hour of sleep. While ODI calculates different metrics than AHI, many patients suffering from obstructive sleep apnea have intermittent oxygen desaturation as well. At sea level, a normal blood oxygen level is considered to be 96-97%. A reduction in saturation is considered mild from 90-95%. Dips into the 80% range are considered moderate, while anything below 80% is severe. For patients with obstructive sleep apnea, ODI combined with AHI are helpful in determining the severity.

Choose Between In-Lab and Home Sleep Testing

While a home sleep test provides valuable information and can detect OSA through breathing patterns, a visit to the lab may be necessary for more intensive sleep disorders. However, sleep centers can gain valuable information about a patient from measuring their sleep efficiency, arousals, AHI, and ODI. This information enables physicians to make a more accurate diagnosis, ensuring that patients are treated properly. To ensure your sleep center is tracking these metrics, it is important to choose sleep lab software that has an easy-to-use dashboard that contains all this information. To learn more about using DreamClear, start a conversation with our team today.