In the present study, platelet count was independently inversely associated with partial MH and MH among 345 Japanese patients with UC.
Platelet count is known as an inflammation marker. Several studies had showed the association between platelet count and outcome among patients with UC. Platelet count among active stage patients was higher than among those with inactive stage UC and healthy subjects in a Greek study of subjects including those with UC and Crohn’s disease [8] and in a Turkish study of subjects with active UC and inactive UC [9]. In a Japanese study of 88 patients with UC, platelet count was positively associated with endoscopic activity [11]. In a Swish study of 280 subjects including those with UC, a positive association between platelet count and endoscopic activity based on a modified Baron score among patients with UC was found [12]. In a prospective study of 183 Japanese UC patients with clinical remission, platelet count among patients with complete mucosal healing (Mayo endoscopic subscore 0) was lower than that among those with partial mucosal healing (Mayo endoscopic subscore1). Furthermore, the change of platelet count from baseline was significantly associated with a shift from complete to partial MH [10]. In a prospective observational study of Japanese UC patients with MH, a platelet count at baseline in the relapse group was significantly higher than that among those in the non-relapse group. Additionally, a platelet count at baseline was significantly associated with relapse among patients with UC after adjustment for several confounding factors [13]. In a Spanish study of 123 patients with UC, a positive relationship between fecal calprotectin level, which is a reliable marker for MH, and platelet count was found [16]. The finding in this study was consistent with these studies that showed the association between platelet count and favorable prognosis. On the other hand, however, a similar association between platelet count and endoscopic activity was reported among patients with Crohn’s disease but not among those with UC [14]. The discrepancies regarding platelet count and MH among patients with UC might be explained, at least in part, by differences in year, duration of UC, sample size, and confounding factors considered.
The underlying mechanism linking platelet count and MH among patients with UC remains unclear, but there are some biologically plausible options. Clusters of differentiation 154 (CD154) plays a central role in co-stimulation and regulation of the immune response via T cell priming and activation of CD40-expressing immune cells [17]. CD 154 expression was found on platelets [18], and mucosal inflammation might elevate platelet count via CD 154 expression.
The platelet-to-lymphocyte ratio (PLR) has emerged as a useful marker revealing shifts in platelet and lymphocyte counts due to acute inflammatory. PLR can be calculated easily from a routine blood test without additional cost. PLR has been reported to be a useful biomarker in the prognosis of various cancers [19]. Several pieces of evidence regarding the association between PLR and UC exist. In a Turkish study of 104 patients with UC and a Korean case control study of 144 subjects including 48 patients with UC and 96 healthy controls, PLR among patients with UC was higher than that in controls, regardless of mucosal remission. PLR among patients with endoscopic active UC was higher than that in patients with endoscopic remission UC [20]. Similarly, in a Korean study, PLR among patients with severe UC was higher than that in patients with mild to moderate UC [21]. In an Italian study of 88 UC patients who started anti-TNF monotherapy, PLR was a useful prognostic biomarker of mucosal healing [22]. Platelet count and PLR might be cost-effective and easy-to-validate parameters for optimal treatment modality. Our findings are consistent with those of previous reports regarding the association between platelets (including PLR) and UC.
To date, MH has been indicated as the therapeutic goal for IBD [3, 23, 24]. Endoscopy is necessary to evaluate MH, but repeated endoscopy is extremely burdensome for patients. Monitoring platelet count might be useful both for patients with UC and their physicians. However, further research is needed to confirm the association between platelet and MH in future.
Our study has a few limitations. First, this was a cross-sectional study; therefore, we cannot conclude that there is a causal relationship between platelet count and MH. Second, most of the patients in this cohort may have been receiving treatment for a considerable period of time since their physicians may have opted to attempt to control inflammation. The long duration of such treatment might have masked the association between platelet count and MH. Third, data regarding fecal calprotectin was not available in this cohort.