Abstract
Background: Limited information is available on the relationship between C-reactive protein (CRP) levels and pain in advanced cancer. Objectives: To investigate the relationship between serum levels of CRP and subtypes of pain. Design: A secondary cross-sectional analysis of a prospective cohort study. Setting/Subjects: Patients with advanced cancer admitted to 23 palliative care units in Japan. Measurements: Patients rated the severity of pain on the numerical rating scale (NRS) and physicians evaluated pain on the integrated palliative care outcome scale (IPOS). Physicians assessed neuropathic pain and breakthrough pain based on their presence or absence. Patients were divided into four groups according to CRP levels. Comparisons were performed using the Kruskal-Wallis test or chi-squared test. To evaluate the relationship between CRP and subtypes of pain, adjusted odds ratios (ORs) and 95% confidence intervals (CIs) in logistic models were calculated. Results: We divided 1513 patients into four groups: low CRP (n = 234), moderate CRP (n = 513), high CRP (n = 352), and very high CRP (n = 414). Spearman's correlation coefficient between CRP and pain NRS and that between CRP and pain IPOS were 0.15 (p < 0.001) and 0.16 (p < 0.001), respectively. In the models of pain NRS and pain IPOS, significantly higher adjusted ORs than in the low CRP group were observed in the very high CRP group (1.81 [95% CI 1.14-2.88], p = 0.01; 1.74 [95% CI 1.18-2.57], p = 0.005, respectively). Relationships were not observed between CRP, neuropathic pain, and breakthrough pain. Conclusions: The results indicated direct relationships between CRP, pain NRS, and pain IPOS.