Apnea-Hypopnea Index (AHI) | What Does Your AHI Score Reveal About Your Sleep Health?

The Apnea-Hypopnea Index (AHI) is the primary metric used to diagnose and determine the severity of sleep apnea. It represents the average number of breathing interruptions per hour of sleep. The calculation is straightforward: the total number of apnea and hypopnea events recorded during a sleep study is divided by the total hours of sleep. An 'apnea' is a complete cessation of airflow for at least 10 seconds. A 'hypopnea' is a partial blockage of the airway, causing a reduction in airflow by at least 30% for 10 seconds or longer, which leads to a drop in blood oxygen saturation or a brief awakening (arousal). For instance, if a person experiences 100 apnea and hypopnea events over 8 hours of sleep, their AHI is 12.5. This index is critical for quantifying the physiological stress experienced during sleep.

The AHI score categorizes the severity of Obstructive Sleep Apnea (OSA) into distinct levels. An AHI of less than 5 events per hour is considered normal for an adult. Mild sleep apnea is defined by an AHI between 5 and 15. Moderate sleep apnea corresponds to an AHI between 15 and 30. An AHI greater than 30 events per hour indicates severe sleep apnea. Each level signifies an increasing risk of health complications. Even mild sleep apnea can lead to symptoms like daytime sleepiness and lack of concentration, while severe cases are strongly associated with significant cardiovascular and metabolic diseases. It is essential to understand that these thresholds are clinical guidelines for assessing health risks and determining the appropriate course of treatment.

While a high AHI is a strong indicator of sleep apnea, it is possible for the score to be transiently elevated by other factors. For example, sleeping on your back (supine position) can worsen breathing disturbances. The consumption of alcohol or sedative medications before sleep can relax throat muscles, leading to more frequent airway collapse. Similarly, nasal congestion from allergies or a cold can temporarily increase the number of respiratory events. However, if a high AHI is recorded consistently, especially alongside symptoms like loud snoring, gasping for air during sleep, and excessive daytime fatigue, it confirms a diagnosis of sleep-disordered breathing that requires medical evaluation.

The AHI is a component of a broader measurement called the Respiratory Disturbance Index (RDI). While the AHI only includes apneas and hypopneas, the RDI also incorporates Respiratory Effort-Related Arousals (RERAs). A RERA is an event where there is increasing respiratory effort for 10 seconds or longer that leads to an arousal from sleep but does not meet the technical criteria for an apnea or hypopnea. Therefore, the RDI provides a more comprehensive measure of sleep fragmentation due to breathing issues. A person can have a low AHI but a high RDI, a condition often seen in Upper Airway Resistance Syndrome (UARS), where frequent arousals disrupt sleep quality without significant oxygen drops.

A persistently high AHI signifies chronic sleep disruption and repeated episodes of oxygen desaturation, which places significant stress on the body. This state of physiological stress is directly linked to numerous serious long-term health problems. The cardiovascular system is particularly vulnerable, leading to an increased risk of hypertension (high blood pressure), coronary artery disease, heart attack, and stroke. Metabolic function is also compromised, heightening the risk for developing insulin resistance and type 2 diabetes. Furthermore, the constant sleep fragmentation impairs cognitive functions, causing issues with memory, attention, and executive function. Mood regulation can also be affected, increasing the prevalence of depression and anxiety. These risks underscore the importance of treating sleep apnea effectively.