What This Means
This research suggests that a simple blood test result — the neutrophil-to-lymphocyte ratio (NLR), calculated by dividing neutrophil count by lymphocyte count from a routine blood draw — can help identify which patients with pulmonary embolism (PE, a blood clot in the lungs) are at higher risk of dying within 30 days. The study looked at 1,525 patients diagnosed with PE at an integrated health system over six years. Current standard practice uses the European Society of Cardiology (ESC) system to classify PE patients as low, intermediate, or high risk, but many patients in the lower-risk categories still have poor outcomes. This study found that patients classified as 'low risk' by ESC criteria but with an NLR of 7 or higher had a 30-day death rate of 10.4%, compared to just 1.2% among low-risk patients with normal NLR — nearly a nine-fold difference. Similarly, among intermediate-risk patients, those with elevated NLR had a 16.2% death rate versus 3.6% in those with normal NLR.
When NLR was added to the ESC risk model, the model's ability to correctly identify who would or would not die within 30 days improved significantly (the C-statistic rose from 0.812 to 0.853, a statistically significant improvement). This means that incorporating NLR could help clinicians better distinguish truly high-risk patients from those who appear lower risk by standard criteria alone. Because NLR is derived from a routine blood test already collected in nearly all hospital admissions, it requires no additional testing or cost.
This research suggests that NLR could be a practical, low-cost tool to improve risk assessment for PE patients, potentially helping to guide decisions about monitoring intensity or treatment. However, because this was a retrospective study at a single health system, the authors emphasize that prospective studies are needed to confirm these findings before NLR is routinely incorporated into clinical PE risk stratification.