A Pilot Study of Urine Oxytocin as an Objective Biomarker for Chronic Pain

Abstract

Background: Measuring pain objectively or quantitatively is difficult. Since urine oxytocin (OXT) concentration has been reported to be potentially associated with chronic pain. Purpose: We conducted a pilot study to evaluate the relationship between changes in numerical rating scale (NRS) score following nerve block and urine OXT concentration in patients with chronic pain. Methods: We investigated 19 chronic pain patients who were admitted to our hospital for nerve intervention. NRS score and urine OXT concentration were assessed before and after the nerve block. Results: NRS scores were 7 [6, 9] and 2 [1, 4] (median [interquartile range]) before and after the treatment intervention, respectively. Urinary OXT levels were 523 [293, 743] and 531 [308, 887] pg/mL (median [interquartile range]) before and after the treatment, respectively. We compared the group with greater improvement in NRS after the treatment intervention and those with less improvement. The group with greater improvement in NRS after the treatment intervention showed a greater increase in OXT level. However, baseline urine OXT concentrations were highly variable in patients with chronic pain and the changes in urinary OXT concentrations were also variable. Conclusion: Based on this pilot study, the utility of urine OXT concentration as an objective biomarker of chronic pain needs further investigation.