The neutrophil to lymphocyte ratio as a novel predictor of asthma and its exacerbation: a systematic review and meta-analysis.

It is widely known that the main white blood cell populations, and neutrophil to lymphocyte ratio (NLR), are involved in systemic inflammation. The usefulness of NLR measurements has been reported in patients with asthma. We performed a systematic review and meta-analysis of studies to investigate the relationship between the NLR and asthma and its exacerbations.We systematically searched PubMed and Embase databases for studies (published between Jan 1, 1950 and Jan 2, 2020; no language restrictions) comparing the NLR values in patients with stable asthma or asthma exacerbations to healthy controls. We assessed pooled data by use of a random-effects model.Of 260 identified studies, 6 were eligible and were included in our analysis (N = 2418 participants). Compared with 439 healthy controls, 743 stable asthma patients in four studies showed significantly greater NLR values (standardized mean difference, SMD, 0.567, 95% CI 0.212-0.922; p = 0.002). Furthermore, compared with 1063 stable asthma patients, 402 asthma exacerbation patients yielded significantly greater NLR values (random effects SMD 1.335, 95% CI 0.429-2.241; p < 0.001).Our meta-analysis showed that the NLR values are a reasonable and easy-to-use marker for asthma and its exacerbations. Further studies, with larger sample sizes and more phenotypes, are required to establish its use as a predictive parameter in asthma.