# Combined red blood cell distribution width and neutrophil-to-lymphocyte ratio and risk of composite cardiovascular events in patients with moderate-to-severe obstructive sleep apnea: a prospective cohort study

## TL;DR

This study finds that combining red blood cell distribution width and neutrophil-to-lymphocyte ratio improves predicting cardiovascular risks in patients with severe sleep apnea.

## Contribution

The novel contribution is the combined RDW-NLR index as a new prognostic marker for cardiovascular events in OSA patients.

## Key findings

- Each 1% increase in RDW and 1-unit increase in NLR independently raise cardiovascular event risk.
- The combined RDW-NLR index improves risk prediction beyond traditional factors in OSA patients.
- The index shows stronger predictive power in older patients and those with poor CPAP adherence.

## Abstract

To evaluate the prognostic association of baseline red blood cell distribution width (RDW), neutrophil-to-lymphocyte ratio (NLR), and their combined index with 3-year composite cardiovascular events in moderate-to-severe obstructive sleep apnea (OSA) patients.

This prospective cohort study enrolled 620 patients with moderate-to-severe OSA (AHI ≥ 15 events/h) from 2020–2022. Participants were categorized by baseline medians into low-risk (both low), intermediate-risk (one high), and high-risk (both high) groups. The primary outcome was composite cardiovascular events. Cox regression, ROC curves, NRI, and IDI assessed predictive performance.

During median follow-up of 36.2 months, 72 events occurred (11.6% rate). Each 1% increase in RDW (HR = 1.32, 95% CI: 1.15–1.52) and each 1-unit increase in NLR (HR = 1.41, 95% CI: 1.20–1.66) were independently associated with cardiovascular events (both p < 0.001). The high-risk group showed 2.98-fold higher risk than low-risk group (HR = 2.98, 95%CI: 1.36–6.52, p = 0.006) with significant dose–response relationship (p = 0.002). The combined RDW-NLR index showed better discrimination (AUC = 0.73, 95%CI: 0.65–0.81) compared with RDW alone (0.65) or NLR alone (0.67). Adding the combined index to traditional risk factors and OSA parameters significantly improved reclassification (NRI = 0.42, p = 0.001; IDI = 0.032, p = 0.009). The association was more pronounced in patients aged ≥60 years, males, and those with poor CPAP adherence.

The combined RDW-NLR index is a simple, accessible prognostic marker of cardiovascular events in moderate-to-severe OSA patients, providing additional risk stratification value beyond traditional risk factors for clinical risk stratification.