2.1. Patient Enrolment and Clinical Specimens

This study was approved by the Ethical Committee for Human Studies of the Medical University of Bialystok, Poland, and was registered on ClinicalTrials.gov ({"type":"clinical-trial","attrs":{"text":"NCT04227223","term_id":"NCT04227223"}}NCT04227223). The inclusion criteria were as follows: age 18–80 years old with LBP, with opioid therapy resulting in a stable NRS (numerical rating scale) value less than 4. Patients more than 80 years old with cognitive disorders who were receiving anti-inflammatory therapy (nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, and other immune-modulating agents) were excluded. The control group included healthy volunteers. Pain related to spinal tissues, as well as radiculopathy pain, with a duration over 3 months was adopted as the definition of chronic LBP.

Firstly, medical histories in the pain clinic were analyzed, and the number of patients with chronic LBP pain with opioid therapy was recorded (n = 77). There were 35 patients with chronic LBP with opioid monotherapy and 42 patients with polytherapy. All patients provided informed consent and were recruited through direct contact with medical staff. The study involved 50 patients, 35 in the study group and 15 in the control group.