Pain Numeric Rating Scale May Be Only Moderately Accurate for Pain Screening

September 20, 2007 — In the primary care setting, the pain numeric rating scale to screen for pain was only moderately accurate in identifying pain in patients, according to the results of a study reported in the August 1 Online First issue and will appear in the October print issue of the Journal of General Internal Medicine.
"Universal pain screening with a 0-10 pain intensity numeric rating scale (NRS) has been widely implemented in primary care," write Erin E. Krebs, MD, MPH, from the Center on Implementing Evidence-Based Practice, Roudebush Veterans Affairs Medical Center in Indianapolis, Indiana, and colleagues. "Universal screening in primary care would be useful if it accurately identified patients with clinically important pain who could potentially benefit from additional pain assessment and management.... The U.S. Preventive Services Task Force (USPSTF) recommends that two criteria be met before a screening test is recommended for widespread use: (1) the test should be sufficiently accurate and capable of detecting a condition earlier than routine care and, (2) screening and early treatment should improve the likelihood of favorable patient outcomes."
In this prospective, diagnostic accuracy study, 275 adult clinic patients were enrolled from September 2005 to March 2006 and were tested for clinically important pain with the use of 2 alternate definitions: pain interfering with functioning (Brief Pain Inventory interference scale[BPI] ≥ 5) and pain motivating a visit to the clinician or being the patient-reported reason for the visit.
A pain symptom being the main reason for a visit to the clinician was reported by 22% of patients, with the most frequently reported pain locations being in the lower extremity (21%) and back or neck (18%).
As a test for pain that interferes with functioning, the NRS had fair accuracy, with an area under the receiver operator characteristic (ROC) curve of 0.76. A pain screening NRS score of 1 was 69% sensitive for pain that interferes with functioning (95% confidence interval [CI], 60 - 78), and multilevel likelihood ratios for scores of 0, 1 to 3, 4 to 6, and 7 to 10 were 0.39 (95% CI, 0.29 - 0.53), 0.99 (95% CI, 0.38 - 2.60), 2.67 (95% CI, 1.56 - 4.57), and 5.60 (95% CI, 3.06 - 10.26), respectively.
Use of the alternate definition of pain that motivates a visit to the clinician yielded similar results.
Limitations of the study include the absence of a well-established gold standard for clinically important pain, potential selection bias, and lack of generalizability to all primary care settings.
"The practice of universal pain screening has become widespread despite a lack of published research evaluating the accuracy and effectiveness of pain screening strategies," the study authors conclude. "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."
The Robert Wood Johnson Foundation provided funding for this study through the Clinical Scholars Program and supported one of its authors. The remaining authors have disclosed financial relationships with the National Institutes of Health and the Department of Veterans Affairs.
J Gen Intern Med. Published online August 1, 2007.