BACKGROUND: Current low back pain (LBP) treatment might be improved by tailoring treatments to subgroup characteristics. The Start Back screening Tool (SBT) and Central Sensitization Inventory (CSI) classify people with LBP into subgroups. It is currently unknown whether linear trends exist regarding somatosensory changes, psychological characteristics, and physical disability across severity levels of the SBT and CSI in patients with LBP. OBJECTIVE: To investigate whether linear trends in psychological variables (kinesiophobia, pain catastrophizing), disability, and somatosensory characteristics exist in a sample of people with acute and chronic LBP in primary care across severity levels based on the SBT and CSI. METHODS: Participants with LBP were recruited in primary care. Demographic, psychological, and disability data were obtained. A comprehensive Quantitative Sensory Testing (QST) protocol was followed. Linear contrast analysis was conducted. RESULTS: Kinesiophobia and pain catastrophizing show significant positive linear trends across the subgroups based on the SBT (p <
0.002) and CSI (p <
0.002 to p = 0.01). Heat pain threshold at the lower leg (p = 0.005) and pressure pain threshold at the lumbar region and lower leg (p = 0.02 and p = 0.04, respectively) show significant negative linear trends within the SBT. Negative linear trends in sensory changes exist within CSI for all pressure pain thresholds and a positive linear trend was seen in δ conditioned pain modulation at the thumb (p = 0.03). CONCLUSION: Kinesiophobia, pain catastrophizing, disability, and pain intensity are positively related with the severity levels based on the SBT and CSI in our participants. Results of somatosensory changes were sometimes related to the severity levels.