The minimum clinically significant difference in visual analogue scale pain score does not differ with severity of pain

OBJECTIVE: To determine whether minimum clinically significant difference in visual analogue scale (VAS) pain score varies according to the severity of pain reported. METHOD: Prospective descriptive study of adult patients in an urban emergency department (ED). On presentation to the ED, patients marked the level of their pain on a 100 mm, non-hatched VAS scale. At 20 minute intervals thereafter they were asked to give a verbal categorical rating of their pain as "a lot better", "a little better", "much the same", "a little worse" or "much worse" and to mark the level of pain on a VAS scale of the same type as used previously. It was pre-defined that patients with VAS pain scores of 30 mm or less would be categorised as having mild pain, those with scores of 70 mm or more were categorised as having severe pain and those from 31 mm to 69 mm, moderate pain. The minimal clinically significant difference (MCSD) in VAS pain score was defined as the mean difference between current and preceding scores when the subject reported "a little worse" or "a little better" pain. RESULTS: 156 patients were enrolled in the study, yielding 88 evaluable comparisons where pain was rated as "a little better" or "a little worse". The MCSD in VAS score in the group overall was 12 mm (95%CI 9 mm to 15 mm). MCSD in VAS score for the "mild pain" group was 11 mm (95%CI 4 mm to 18 mm), for the "moderate pain" group 14 mm (95%CI 10 mm to 18 mm) and for the severe pain group, 10 mm (95%CI 6 mm to 14 mm). There is no statistical difference between the MCSD in VAS score between the severity groups. CONCLUSIONS: The MCSD in VAS pain score does not differ with the severity of pain being experienced.