Anchoring the Numeric Pain Scale Changes Pain Intensity Reports in Patients With Chronic But Not With Acute Pain

Background Despite enormous differences between acute and chronic pain, the numeric pain scale (NRS) is commonly used in pain research and clinical practice for assessing the intensity of both acute and chronic pain. The use of this scale has been challenged as it may fail to accurately reflect the pure intensity of chronic pain. Aim To compare the effect of anchoring the NRS on the intensity of pain reported by patients with acute vs. chronic pain. Methods Patients with acute postoperative or chronic pain (n = 100/group) were requested to rate their: current clinical pain intensity on an NRS from 0 to 100; the intensity of an anchoring pain event on the same scale; and subsequently to rate again their current pain intensity while making reference to the reported intensity of the pain event. The magnitude of correction was compared between the 2 groups. Results The anchoring pain was rated identically between the groups. However, following anchoring, patients with chronic pain made a significantly larger correction of their pain intensity than did those with acute pain (mean +/- standard deviation = 9 +/- 9, median [interquartile range] = 10 [0 to 10] vs. 3 +/- 7, 0 [0 to 5], respectively; P < 0.0001). More patients in the chronic pain group corrected their pain intensity. Logistic regression showed that chronic pain and female gender significantly increased the likelihood of making the correction (chronic pain: odds ratio 7.2, 95% confidence interval 3.5 to 15.1, P < 0.0001; female gender: odds ratio 2.8, 95% confidence interval 1.4 to 5.5, P < 0.0001). Conclusion The results suggest that anchoring the NRS can potentially improve the accuracy of reported chronic pain intensity.