Measuring pain intensity in older adults. Can the visual analogue scale and the numeric rating scale be used interchangeably?

OBJECTIVES: Visual analogue scale (VAS) and numeric rating scale (NRS) are two commonly used instruments for measuring pain intensity. Both instruments are validated for use in both clinical and research settings, and share a range of similar aspects. Some studies have shown that the two instruments may be used interchangeably, but the results are conflicting. In this study we assessed whether the VAS and the NRS instruments may be used interchangeably when measuring pain intensity in older adults. METHODS: Data were collected in a cross-sectional study, as part of the follow-up in a larger longitudinal study conducted at the Akershus University Hospital, Norway 2021 to 2022 and included 39 older adults aged ≥65. Participants were regarded as a normal older adult population as they were not recruited on basis of a specific condition or reports of pain. The participants were asked to rate their pain intensity on an average day using VAS and NRS. Bland-Altman analysis was performed to assess agreement between the two instruments. RESULTS: Thirty-seven participants with mean (SD) age of 77 (5.9) were included in the analysis. Mean (SD) pain assessed by VAS and NRS was 2.8 (1.8) and NRS 4.7 (2.2), respectively. A mean difference (SD) of 2.0 (1.9) between the scores of the two instruments was statistically significantly different from zero (p < 0.001) confirming bias. The 95% limits of agreement were estimated to be -1.7 to 5.7. A post-hoc analysis, removing an outlier, resulted in similar conclusions. CONCLUSION: There was poor agreement between the VAS and NRS scale for measuring pain intensity in older adults. This suggests that the two instruments should not be used interchangeably when assessing pain intensity in this population. ETHICAL APPROVAL: Regional Committees for Medical and Health Research Ethics 2016/2289. TRIAL REGISTRATION: NCT03162081, 22 May 2017.