C5a in the peripheral plasma of female fibromyalgia patients is elevated but not related to pain sensitivity as in healthy controls

Although evidence from basic studies indicates that C5a induces hyperalgesia, knowledge from studies of humans is limited. This comparative analysis of the peripheral blood C5a concentration of women diagnosed with fibromyalgia (FM) who exhibited widespread pain and that of female healthy controls (HCs) was done to assess possible correlations of C5a concentration with pain threshold. The data of 30 patients with FM and 29 HCs were included in the analysis. C5a concentration in the peripheral blood was quantified by ELISA, and the cold pain threshold (CPT) was assessed. The correlation between C5a concentration and CPT was analyzed using the Spearman correlation coefficient, and the peripheral blood C5a concentrations of FM and HC were compared by t-test. The mean (standard deviation) peripheral blood C5a concentrations of FM and HC were 12.7 (6.48) ng/ml and 8.82 (4.79) ng/ml, respectively (p = 0.0114). Although no significant relation was observed between CPT and C5a concentration in FM (R = − 0.12, p = 0.52), a significant correlation was found for HC (R = 0.41, p = 0.03). The results suggest that C5a would be a potential biomarker for the pain sensitivity of women and give new insights into the pathophysiology of FM.