Development of a tool for objectively measuring somatic pain in the low back region based on a longitudinal diagnostic study conducted in Karachi, Pakistan

OBJECTIVES: This study aimed at devising an objective method for quantifying pain in the low back region using pressure pain threshold (PPT) and demographic factors as predictive variables. METHODS: The research was conducted in two phases. Phase I was a longitudinal exploratory study conducted on 49 men aged 18–50 years with chronic low back pain (CLBP) recruited using non-probability purposive sampling. We used Visual Analogue Scale to record pain intensity and pain affect, and Disability Rating Index to record associated disability. PPT was measured on 12 different locations on the lower back using a manual algometer. These measurements were taken from each participant in 1 to 6-follow-up visits, depending on improvement in the individual’s symptoms. In phase II additional 33 subjects, both men and women with varying durations of low back pain were recruited using non-probability convenience sampling. Repeated measures ordinal regression and receiver’s operating characteristic curve analyses were performed to develop predictive models using STATA V.16.0 and R V.3.5.2 software. These models were given an interface using Microsoft Excel. A p value of <0.05 was considered statistically significant. RESULTS: Higher PPT scores, increased lean body mass, lean physique and a longer duration of CLBP were associated with a reduction in CLBP intensity, affect and disability. Advancing age was associated with an increase in these outcomes. Collectively, these factors were found to predict pain intensity, affect, and disability with 63%–65% diagnostic accuracy in phase I, however, this diagnostic accuracy increased to 65%–78% in phase II. CONCLUSION: We developed a new outcome tool ‘Pain Calculator’ that can objectively measure low back pain with sufficient statistical accuracy. With further refinement, this tool in the future can be configured to measure somatic pain in different regions as well, affording clinicians and researchers much-needed objectivity while recording pain levels. TRIAL REGISTRATION NUMBER: NCT04482075.