Looking beyond AHI to get the whole picture

For decades, obstructive sleep apnea (OSA) has been primarily diagnosed and stratified based on the apnea-hypopnea index (AHI), a measure of the number of apneas and hypopneas per hour of sleep. An increasing body of research shows that AHI as a sole marker may not provide a full diagnostic picture, thereby missing some patients who may have or should be treated for OSA.

OSA is more common than many think, with the total number of people impacted far exceeding the number actually diagnosed and treated. According to estimates, nearly 1 billion people are affected by sleep apnea, with prevalence as high as 50% of the population in some countries.¹ Sadly, diagnosis rates lag, with as many as 80% of people with OSA in the United States remaining undiagnosed.²

Sole reliance on AHI leaves women behind

While AHI is, and should remain, an important metric in the assessment of OSA, the combined prevalence and significant underdiagnosis demonstrates the need for diagnostic criteria that goes beyond AHI.

An AHI-only approach to diagnosis may well contribute to the problem of underdiagnosis, especially among individuals who do not fall into the stereotypical view of a patient with OSA. For example, women with OSA typically experience lower AHI, with shorter apneas and less severe hypopneas, meaning that a reliance on AHI alone can severely disadvantage female patients.³ Women are routinely less likely to be referred for sleep testing, less likely to be diagnosed, and less likely to be treated for OSA even though they suffer a similar – or higher – symptomatic burden.⁴

To have people living with untreated OSA simply because they have a disproportionately high symptomatic burden compared to their AHI score is not acceptable. By remaining undiagnosed or incorrectly stratified, their risk of being untreated or incorrectly treated opens the door to additional—yet avoidable—health challenges.

New approaches aim to improve the AHI status quo

The historical AHI-only approach to OSA diagnosis has been recognized as insufficient, leading to researchers within the global sleep health community to explore alternatives that incorporate AHI alongside other indicators to assess OSA in patients.

Since 2021, Sweden has implemented new guidelines for OSA that include AHI, but also OSA-related symptoms, cardiometabolic comorbidities, and age to determine severity of OSA.⁵ Similarly, a method known as the Baveno classification, first published in 2018 and updated in 2024, has taken a multicomponent approach to classifying OSA severity focusing on analyzing the severity of both symptoms and cardiovascular risk.^6,7

While both the Swedish and Baveno methods aim to improve the diagnosis and stratification of OSA by considering multiple factors along with AHI, they share three potential issues that may limit their ability to effectively identify patients with OSA.

First, the focus on cardiovascular comorbidities requires a high level of collaboration between primary care physicians, cardiologists and sleep specialists—a level that rarely exists across these three providers. Second, the reliance on patient-reported symptoms requires the average person to know the symptoms of OSA beyond sleepiness and when to raise them with their doctor. Finally, the focus on symptomology requires a level of training about OSA that the average primary care provider often lacks.

These realities mean that while a model like Baveno may facilitate increased treatment among patients with high cardiovascular risk, it may exclude others, especially those with low AHI. Consider this scenario: A patient has a low to moderate AHI, low cardiovascular risk and high symptomology in the form of nightly awakenings, insomnia and depression —but a low awareness that these may be symptoms of OSA. Due to their low awareness, the patient does not discuss their symptoms with the physician. The physician, in turn, is only aware of the AHI level and cardiovascular risk. In the Baveno criteria, this can mean firmly no treatment or only a light potential to treat based on the discretion of the patient and provider together. In essence, this cycle may only serve to elevate and further solidify the role of AHI in the diagnosis and stratification of OSA—exactly the opposite of what was intended with Baveno from the beginning.

Additional markers that may further broaden the view

In addition to AHI, symptoms and cardiovascular risk, other markers may build on what the Baveno criteria and Swedish guidelines have started. Oxygenation patterns in patients, for example, can provide a valuable window into the severity of OSA symptoms and the impact on comorbid cardiovascular conditions.

The oxygen desaturation index (ODI) is currently captured. However, this merely indicates the presence and timing of any desaturation of the blood oxygen. One frequently discussed measure is is the hypoxic burden (HB) which indicates not only the number of desaturations, but also the depth and duration—and therefore the severity—of these events. Current research into the role of oxygenation in patients with OSA includes additional biomarkers like sleep apnea specific heart rate response and pulse wave amplitude drops (PWAD).^8-13 These measures may allow a better understanding of cardiovascular risk and help to identify both the severity of OSA and the potential benefits of treatment. Streamlined versions of these algorithms are being evaluated and may be included in future versions of the Baveno criteria or other diagnostic approaches.^14,15

Where OSA diagnostics go from here

The need to evolve the diagnostic standards for OSA is not a question of if, but of when and how. The status quo poses a significant risk to patients by preventing treatment for many who need it. By taking a multimodal approach to diagnosis and stratification, coupled with increasing general awareness of sleep apnea and its symptoms, we can elevate the patient experience at all stages of the journey. More people with OSA can be accurately diagnosed, receive appropriate treatment and, potentially, improve their overall health outcomes.