Comparison of Measures of Pain Intensity During Sickle Cell Disease Vaso-Occlusive Episodes

We aimed to determine the minimal clinically important difference (MCID) in pain severity and agreement between the visual analog scale (VAS) and the verbal numeric rating scale (NRS) in people with sickle cell disease (SCD) experiencing an acute vaso-occlusive episode in the emergency department. In the COMPARE-VOE trial (NCT03933397), participants were administered the VAS (0–100), NRS (0–100), and descriptor scale (a lot better, a little better, same, a little worse, much worse) every 30 minutes while in the emergency department. We analyzed data from 100 participants (mean age 30.2 years; 61% female). We calculated the mean differences and 95% confidence intervals (CIs) between current and preceding scores when the participant reported a little worse or a little better pain for each scale (255 VAS and 150 NRS observations) to assess the MCID for the VAS and NRS. Pearson correlation and the Bland-Altman method were used to assess the agreement among 411 paired VAS and NRS observations. Our results indicated that the MCID for the VAS was 8.77 mm (95% CI: 7.43 mm, 10.83 mm) and the NRS was 8.29 (95% CI: 6.47, 11.60). The VAS and NRS scales had a correlation of .88 (P < .001). The Bland-Altman method indicated a mean difference of −4.6 ± 1.96 and the 95% limits of agreement ranged from 20 to −29. Despite high correlation, there was considerable variability of agreement between the VAS and NRS scales, indicating that these scales are not interchangeable to assess pain during a vaso-occlusive event. Perspective: The MCID in pain severity for individuals with a SCD vaso-occlusive episode using the VAS (8.77 mm) is lower than previously reported, and the MCID for NRS was 8.29. The agreement between the VAS and NRS was determined and the scales cannot be used interchangeably to measure SCD pain intensity.