We found that the pain screening NRS had only modest accuracy for identifying patients with clinically important pain in an academic primary care clinic. Even a pain screening cutoff score of 1 missed nearly a third of patients with clinically important pain.
Why did the pain screening NRS miss patients with clinically important pain? First, it is possible that this simple measure cannot be expected to identify all clinically important pain in primary care. Pain is a multidimensional experience, and this dimensionality has important implications for its measurement.8,28
In settings where pain is often chronic and complex, the simple pain screening NRS may fail to identify patients with pain-related suffering driven by functional limitations, illness worry, or other factors.
There are more focused potential explanations for the poor performance of the pain screening NRS, including the time frame and wording of the question. Because it focuses on current pain, the NRS might miss intermittent symptoms. In addition, we found that “pain” was not the preferred word for some patients to describe their subjective experience. For example, one participant reported difficulty answering the questions because “I feel great discomfort, but it is different than pain.”
To our knowledge, this is the first published study to evaluate the accuracy of pain screening in primary care. Our study has several strengths. First, we evaluated the most commonly used pain screening measure under real primary care clinical conditions. In addition, we collected detailed prospective information about pain and recruited a diverse group of primary care patients with a broad spectrum of pain and other medical problems.
This study also has several potential limitations. First, there is no well-established gold standard for clinically important pain. However, we believe our strategy for operationalizing clinically important pain is well supported by the available literature and clinical experience. Functional impairment has been used many times previously to classify pain severity.12–17
Pain as a reason for the visit was chosen as the second definition because of its patient-centeredness and clinical relevance. Whereas we recognize that not all clinically important pain will be included in either of these definitions, we believe a pain screening test should at least identify patients with pain that is functionally impairing or motivates a visit. Second, selection bias is a potential concern. Participants were enrolled when the research assistant was available. In addition, 34% of invited patients declined to participate, and 14% initially agreed but did not complete the interview. We do not believe these factors biased our results. Clinic procedures and staffing on study enrollment days did not differ from other days, and enrollment was not limited to certain times or days of the week. Patients who failed to complete the interview had similar demographic characteristics, pain scores, and reasons for the visit as completers. In addition, demographics of our study participants closely matched those of the clinic population. Finally, our findings are limited to a single academic Internal Medicine clinic; thus, our results cannot be generalized to all primary care settings.
To date, there is little empirical support for the hypothesis that routine assessment and documentation of pain will improve pain management in primary care. A recent retrospective study found no improvement in quality of pain care at a Veterans Affairs general medicine clinic after implementation of the “Pain as the 5th Vital Sign” campaign, which uses a pain intensity NRS to screen for pain.29
Universal pain screening may have substantial costs in primary care, where numerous acute, chronic, and preventive care priorities compete for limited physician and nursing time.30
For example, primary care physicians do not have time to complete even the preventive services that have been rigorously evaluated and recommended by the USPSTF.31
In this resource limited environment, mandated initiatives like universal pain assessment may have unintended effects on patient care, clinic efficiency, clinician and patient satisfaction, and medicolegal risk.
In conclusion, the practice of universal pain screening has become widespread despite a lack of published research evaluating the accuracy and effectiveness of pain screening strategies. Our results suggest that the most commonly used measure for pain screening may have only modest accuracy for identifying patients with clinically important pain in primary care. Further research is needed to determine whether pain screening improves patient outcomes in primary care.