Associations between the neutrophil-to-lymphocyte and the platelet-to-lymphocyte ratios and the presence and severity of psoriasis: a systematic review and meta-analysis

The diagnosis of psoriasis, an immune-mediated disease that affects 2% of the population in Western countries, is largely based on history and clinical examination. The aim of this systematic review and meta-analysis was to investigate the associations between the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) and the presence and clinical severity of psoriasis. A systematic literature search was conducted in PubMed, Web of Science, and Scopus, from inception to January 2018. Twelve case–control studies enrolling 1067 psoriasis patients (537 males and 530 females) and 799 healthy controls (404 males and 395 females) were included in the meta-analysis. The NLR was evaluated in all the studies, while the PLR was assessed in four studies. Pooled results showed that both the NLR and the PLR values were significantly higher in patients with psoriasis (SMD = 0.69, 95% CI 0.53–1.85, p < 0.001, and SMD = 0.40, 95% CI 0.12–0.68, p = 0.006, respectively). There were no significant differences in NLR values according to the severity of disease (p = 0.52). The NLR and the PLR are significantly associated with the presence, but not with the severity, of psoriasis. Further studies are required to determine the additional utility of these haematological indexes in the diagnosis of psoriasis.