The Abbey Pain Scale: not sufficiently valid or reliable for assessing pain in patients with advanced cancer

The Abbey Pain Scale (APS), an observational pain assessment tool, is used in patients with cancer who cannot verbalize their pain. However, when psychometrically tested, the APS did not display sufficient validity or reliability, so it cannot be recommended for clinical use in patients with advanced cancer. Patients with advanced cancer can be unable to verbalize their pain. The Abbey Pain Scale (APS), an observational tool, is used to assess pain in this setting, but has never been psychometrically tested for people with cancer. The aim of this study was to assess the validity, reliability, and the responsiveness of the APS to opioids for patients with advanced cancer in a palliative oncology care setting. Patients with advanced cancer and poor performance status, drowsiness, unconsciousness, or delirium, were assessed for pain using a Swedish translation of the APS (APS-SE) and, if possible, the Numeric Rating Scale (NRS). The assessments using APS were conducted simultaneously, but independently, by the same raters on two separate occasions, approximately one hour apart. Criterion validity was assessed by comparing the APS and NRS values using Cohen's kappa (κ). Inter-rater reliability was determined using the intraclass correlation coefficient (ICC), internal consistency using Cronbach's α, and responsiveness to opioids using the Wilcoxon signed-rank test. Seventy-two patients were included, of whom n = 45 could rate their pain using the NRS. The APS did not detect any of the n = 22 cases of moderate or severe pain self-reported using the NRS. The APS at first assessment had a κ of 0.08 (CI: −0.06 to 0.22) for criterion validity, an ICC of 0.64 (CI: 0.43-0.78) for inter-rater reliability, and a Cronbach's α of 0.01 for internal consistency. The responsiveness to opioids was z = −2.53 (p = 0.01). The APS was responsive to opioids but displayed insufficient validity and reliability and did not detect moderate or severe pain as indicated by the NRS. The study showed a very limited clinical use of the APS in patients with advanced cancer.