The neutrophil-to-lymphocyte ratio (NLR), calculated as a simple ratio between the neutrophil and lymphocyte counts measured in peripheral blood, is a biomarker which reflects the balance between two aspects of the immune system: acute and chronic inflammation (as indicated by the neutrophil count) and adaptive immunity (lymphocyte count).

NLR has been extensively evaluated and shown to be associated with outcome and predict disease course among patients with a variety of medical conditions including ischemic stroke, cerebral hemorrhage, major cardiac events and sepsis and infectious diseases. Furthermore, in cancer patients higher NLR has been associated with poor prognosis. These adverse associations may reflect the contributions of severe inflammation and poor immune function to the progression of these diseases.

By extension, NLR may be predictive of mortality in the general population, and thus the overall impact of inflammation and immunity on health. Several studies have reported that higher NLR was significantly associated with overall mortality and mortality due to cardiovascular disease, but not with mortality due to cancer. In addition, it is important to evaluate associations of NLR with cause-specific mortality over different intervals of follow-up time, because associations over short intervals after baseline measurement of NLR predominantly reflect the effects of disordered inflammation or immunity for people who already have these medical conditions. In contrast, associations over intervals of several years reflect effects of these processes on both the incidence of disease and survival after diagnosis. While some studies have assessed associations over different follow-up intervals for mortality due to cardiovascular disease, cancer or stroke, no study has systematically assessed such associations for multiple diseases.

Additional notes:

The NLR should always be interpreted in the clinical context of the patient and not be used in isolation to diagnose or rule-out disease, however it may be a more useful test than ones medicine routinely uses, like the WBC.

References:

Song, M., Graubard, B.I., Rabkin, C.S. et al. Neutrophil-to-lymphocyte ratio and mortality in the United States general population. Sci Rep 11, 464 (2021). https://doi.org/10.1038/s41598-020-79431-7 [L]