Convergent validity of a person-dependent definition of a low back pain flare.

Exacerbations of existing low back pain (LBP) or new LBP episodes are colloquially referred to as "flares." Although the experience of flares is common to many people with LBP, few validated measures enable people to self-report if they are experiencing a flare. This study examined the convergent validity of a person-dependent definition of flares ("a worsening of your low back pain that lasts from hours to weeks") as compared with (1) LBP intensity, (2) LBP-related pain interference, and (3) analgesic use, in a large, prospective research study of Veterans with LBP. Veterans seeking care for LBP (n = 465) were followed prospectively for up to 1 year. Participants completed up to 36 scheduled surveys and additional patient-initiated surveys (triggered by the onset of new flares) over follow-up. Each survey inquired about current flare status, pain intensity measured on a 0 to 10 numeric rating scale (NRS), LBP-related pain interference, and analgesic use. Linear mixed-effects models estimated the association between current flare status and pain intensity, with and without adjustment for potential confounding factors; secondary analyses examined associations with pain interference and analgesic use. In longitudinal analyses of 11,817 surveys, flare status was significantly associated with a 2.8-NRS point greater pain intensity (P < 0.0001), with and without adjustment for other factors. Statistically significant associations were found between flare status and LBP-related pain interference and analgesic use. New flare periods were associated with impacts on coping, functional limitations, and mood/emotions. These findings support the convergent validity of a person-dependent flare definition.