Interpreting Hypopnea Scoring Disparities: Methodological Considerations in Recent OSA Diagnostic Research

Dr. Chelsie Rohrscheib, Ph.D.

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A recent retrospective analysis by Subramanian et al. examined whether application of the 4% versus 3% hypopnea scoring criteria resulted in racial or sex-based differences in obstructive sleep apnea (OSA) diagnosis among 1,354 adults undergoing first-time in-lab polysomnography at a single urban academic medical center [1]. 

The authors reported no significant racial differences in diagnostic classification after adjustment for age, sex, body mass index (BMI), and comorbidities, while female participants demonstrated significantly lower odds of meeting the 4% hypopnea criterion. These findings contribute to an ongoing discussion regarding hypopnea definition, pulse oximetry performance, and access to OSA diagnosis. However, several methodological considerations warrant careful interpretation of the results.

A primary limitation relates to the use of self-reported race as a surrogate for skin pigmentation. Pulse oximetry bias is fundamentally driven by optical absorption properties of melanin rather than racial identity. Substantial heterogeneity in skin tone exists within racial categories, and overlap occurs across groups. As a result, race-based classification introduces exposure misclassification that may attenuate detection of true oximetry-related effects. Without direct measurement of skin pigmentation, conclusions regarding the absence of pulse oximetry bias at the diagnostic level remain inherently constrained.

The clinical characteristics of the study population also limit generalizability. Participants were drawn from a tertiary-care academic sleep laboratory and represented individuals referred for in-lab polysomnography, a group typically enriched for moderate-to-severe disease. In this cohort, Black participants demonstrated higher mean BMI and higher AHI under both scoring definitions compared with other racial groups. Greater underlying disease severity increases the likelihood of surpassing the 4% desaturation threshold, potentially masking oximetry-related underestimation of hypoxemia. This severity enrichment may therefore obscure disparities that could emerge in community-based or lower-severity populations, where diagnostic thresholds are more sensitive to small differences in measured oxygen desaturation.

Importantly, the study evaluated diagnostic eligibility rather than signal-level oximetry performance. While diagnostic classification is clinically meaningful, it does not directly assess whether hypoxic events are systematically underestimated in certain populations. Pulse oximetry bias operates at the physiologic measurement level, influencing desaturation depth and event detection before aggregation into summary indices such as AHI. Without examination of raw oxygen saturation signals, desaturation amplitudes, or event-level discrepancies, it is not possible to determine whether measurement bias was present but insufficient to alter categorical diagnosis within this cohort.

The retrospective design further limits control over key variables known to influence hypopnea expression, including sleep position, REM-specific respiratory events, arousal burden, medication use, and night-to-night variability. These factors are particularly relevant to phenotype-specific OSA presentations and may differentially affect diagnostic thresholds across sex and racial groups. Additionally, approximately 30% of initially identified records were excluded due to missing BMI or comorbidity data, introducing potential selection bias. Sensitivity analyses to assess the impact of these exclusions were not reported.

In contrast to the null racial findings, the observed sex-based disparity aligns with prior literature. Female participants were significantly less likely to meet the 4% hypopnea criterion even after multivariable adjustment. This finding is consistent with established physiologic differences, including lower upper airway collapsibility, lower loop gain, greater REM predominance, and higher prevalence of arousal-associated hypopneas among women. These characteristics reduce the likelihood of meeting strict desaturation thresholds despite clinically relevant sleep-disordered breathing. As a result, reliance on the 4% rule may systematically limit diagnostic eligibility for female patients, potentially delaying treatment in a population already prone to under-recognition of OSA.

Taken together, the findings by Subramanian et al. should be interpreted within the context of these methodological constraints. The absence of racial differences in diagnostic classification within this specific tertiary-care cohort does not negate extensive evidence demonstrating pulse oximetry inaccuracy in individuals with darker skin pigmentation across multiple clinical settings. Rather, it underscores the need for more granular investigation using direct measures of skin tone, prospective multi-center designs, inclusion of milder disease phenotypes, and signal-level analysis of oxygen saturation.

Future studies should prioritize these elements to better characterize how hypopnea definitions and oximetry performance interact with demographic and physiologic variability. Such work is essential to ensure that diagnostic criteria accurately reflect disease burden across diverse populations.

Finally, the consistent demonstration of sex-related disparities reinforces concerns regarding the continued use of the 4% hypopnea rule, particularly by payers. Evidence increasingly supports the 3% criterion as more inclusive of clinically meaningful disease and more reflective of cardiovascular risk. Adoption of the 3% rule may improve diagnostic equity and access to care, especially for women and patients with non-desaturating or REM-predominant OSA phenotypes.

While the current study adds valuable data to the discussion, broader and more precise investigations are needed before concluding that existing hypopnea scoring practices are equitable across populations.

 

1. Subramanian S, Miner AE, Auerbach S, Spector A. Sex, but Not Race, Influences OSA Diagnosis When Applying the 4% Versus 3% Hypopnea Scoring Rule. J Clin Med. 2025 Dec 15;14(24):8878. doi: 10.3390/jcm14248878.