|Author||Methodological Quality||Study Design||Data Collection||Participant Information|
|Gebhardt et al., 2006 ||6||Prospective cohort|
NSLBP group received 3 weeks of daily treatment during clinical period (including oral pain medication and physical therapy).
|NSLBP group data collected on days 0, 3, 7, 10, 14, 17 and 21 (clinical period) and after 2, 3 and 6 months (follow-up).||41 participants with NSLBP; 1572 controls representative of German population|
NSLBP defined as over 3 months of chronic myofascial LBP with absence of radicular symptoms or motor deficits.
|Heffner et al., 2011 ||4||Case-control|
Chronic NSLBP group compared to healthy control group of age and sex-matched individuals over 24 h period.
|Blood samples taken and questionnaires completed in morning of Day 1 (time 1). Sleep quality and pain recorded morning of Day 2 (time 2).||25 participants with chronic NSLBP;|
25 age- and sex-matched controls without pain.
Chronic NSLBP defined as more than 6 months pain duration without history of inflammatory disease, spine surgery, orthopaedic injury or neurologic signs.
|Klyne et al., 2017a ||7||Case-control|
Participants were divided by: (1) those with and without NSLBP, and (2)“high pain,” those with moderate-to-severe NSLBP (VAS ≥4), “low pain,” those with mild LBP (VAS < 4), and controls.
|Blood samples collected at one time point and questionnaires completed with 24 h.||99 participants with acute NSLBP;|
55 healthy controls
Acute NSLBP was defined as an episode within < 2 weeks prior following at least 1 month with no pain. Episodes lasted > 24 h and caused functional limitation and care seeking.
|Klyne et al., 2018a ||6||Prospective cohort|
Participants were categorized into NSLBP and control groups. NSLBP participants were then categorized based on their past 6 months of pain and disability status.
|Blood samples collected at baseline and 6 months. Pain questionnaires completed within 24 h of sampling and every 2 weeks for 6 months.||Demographics are reported above for Klyne 2017 study.|
NSLBP participants were categorized in 3 groups based on their NRS pain scores and RMDQ scores at 6 months: (1) unrecovered - increased/unchanged pain and disability from baseline, or a pain score ≥ 7/10 (unrecovered) (2) partially recovered - pain and/or disability is decreased but not yet fully recovered from baseline, and (3) recovered - no pain and disability. NSLBP participants (N = 25) without these data were not categorized.
|Luchting et al., 2016 ||4||Case-control|
NSLBP group compared to neuropathic pain group and healthy control group
|Blood samples taken once between 9:00 and 9:30 AM. Self-reported pain, stress and depression questionnaires administered.||19 participants with chronic NSLBP; 19 participants suffering from neuropathic pain;|
19 subjects that are pain-free.
NSLBP defined as persistent low back pain not attributable to a detectable pathology
|Sturmer et al., 2005 ||5||Prospective cohort|
NSLBP group compared to acute sciatic pain group for duration of 6 months.
|Blood samples collected and outcomes assessed on day 3, 7, 10, 14, 17, 21 and after 2, 3, and 6 months.||41 participants with chronic NSLBP (65.8% female, mean age 42.4 years, mean BMI 27.7 kg/m2 SD 6.8, 41.5% current smokers)|
NSLBP defined as LBP for at least 6 weeks attributable to the spine and without signs of specific pathology.
|Wang et al., 2010 ||7b||Prospective Cross-sectional study|
NSLBP group was compared to a NSLBP with depression group, and healthy age and sex-matched control group at one time point.
|Blood samples collected and outcomes assessed at one time point.||29 participants with chronic NSLBP; 29 patients with NSLBP and depression; 29 age and sex matched healthy controls.|
NSLBP defined as LBP of at least 6 months duration in absence of specific etiology. Leave from work for at least 6 weeks.
|Wang et al., 2008 ||4||Case-control|
Matched pair design for a 6 month duration. NSLBP group underwent 3 weeks of inpatient biopsychosocial and physical therapy.
|Blood samples collected and outcomes assessed at Day 0, 10, 21 and 6 months.||120 participants with chronic NSLBP; 120 age and sex matched controls with no LBP in the past year (43.3% female, mean age 45.4 SD 11.4 years, mean BMI 27.1 kg/m2 (18.7–47.8), 31.7% current smokers)|
NSLBP defined as unspecific myofascial chronic LBP, present for a least 3 months. Subjects with specific causes of pain or other locations of pain were excluded. Leave from work for at least 6 weeks.