Pain Numeric Rating Scale May Be Only Moderately Accurate for Pain Screening CME/CE
News Author: Laurie Barclay, MD
CME Author: Désirée Lie, MD, MSEd
Disclosures

Release Date: September 20, 2007; Valid for credit through September 20, 2008 Credits Available

Physicians - maximum of 0.25 AMA PRA Category 1 Credit(s)™ for physicians;
Family Physicians - up to 0.25 AAFP Prescribed credit(s) for physicians;
Nurses - 0.25 nursing contact hours (None of these credits is in the area of pharmacology)



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.

October 2007;00:000-000.

Clinical Context
Approximately 20% of primary care patients experience chronic pain, and pain screening is intended to improve the quality of pain management by systematically identifying patients with pain in clinical settings, but currently there is no commonly accepted gold standard for clinically important pain. The NRS on which patients rate their pain as 0 ("no pain") to 10 ("worst pain") has become the most widely used instrument for pain screening. The potential advantages of the NRS are it is short, easy to administer, and is validated as a measure of intensity of pain in populations with known pain. However, no studies have evaluated its accuracy as a screening test to identify patients with clinically important pain.

This is a prospective diagnostic accuracy study of consecutive patients presenting to a primary care outpatient clinic to compare the NRS used as a screening tool with 2 functional measures of pain: the BPI interference scale and a question on pain that motivates a visit to the clinician.

Study Highlights
Included were consecutive patients presenting to 1 outpatient clinic who consented to completing a face-to-face interview after the clinician visit.
Excluded were patients who did not speak English.
As a routine, the NRS was completed with the vital signs for all patients, and a nurse documented the answers in the electronic medical record.
Patients with an NRS score of 1 or higher were oversampled for analysis.
20% of the sample had an NRS score of 0.
Participants were interviewed after the clinician visit.
Nursing notes, dictated physician notes, and problem lists were abstracted from the medical records after the interview.
The BPI was administered.
The BPI measures 7 domains: general activity, mood, walking ability, normal work, relationships with other people, sleep, and enjoyment of life.
Possible BPI scores ranged from 0 ("does not interfere") to 10 ("interferes completely"), and a lead-in question was used to define pain as other than "everyday pains such as minor headaches, sprains, and toothaches."
2 questions were used to elicit the reason for the visit: "What is the main reason for your visit?" and "What other concerns would you like to talk to your doctor about today?"
Responses were classified as pain symptom, nonpain symptom, or other.
Because there is no criterion standard definition of clinically important pain, the investigators operationalized the definition as pain that interferes with functioning and pain that motivates a clinician visit.
A score of 5 or greater on the BPI interference scale was used as the reference standard for pain interfering with function.
The ROC curves for the NRS were compared with the reference standards for function and motivation.
Of 548 patients approached, 357 consented and 77% were included in the analysis.
Mean age of the patients was 55 years, each patient had an average of 1.9 conditions, 80% saw their regular physician, and 46% saw a resident physician.
40% of patients reported a pain symptom as the reason for the visit, with 22% reporting the pain as a primary and 18% as a secondary concern.
Among participants with an NRS screening score of 1 or greater, the mean score was 6.0.
Most patients reported musculoskeletal pain, with the most common locations in the lower extremity (21%) and back or neck (18%).
55% of patients overall and 77% with at least 1 pain symptom reported persistent pain for 6 months or longer.
The area under the ROC curve for the NRS vs the BPI (for a score of ≥ 5) was 0.76.
The lowest possible cut-off point (an NRS score of 1) was 69% sensitive and 78% specific for functional interference.
Thus, nearly one third of patients with pain-related functional interference had an NRS score of 0.
At the NRS score of 4, sensitivity was 64% and specificity was 83%.
If the pretest probability of pain-related functional interference was 40%, the post-test probabilities corresponding to scores of 0, 1 to 3, 4 to 6, and 7 to 10 would be 21%, 40%, 64%, and 79%, respectively.
The area under the ROC curve for the NRS vs the motivation for a clinician visit was 0.78.
21% of patients who reported pain as the primary reason for the visit and 28% of those who reported pain as any reason for the visit had a NRS score of 0.
The sensitivity of an NRS score of 1 was 71%, and the specificity was 81%.
An NRS score of 4 had a sensitivity of 63% and a specificity of 83%.
The study authors concluded that the NRS had only moderate accuracy for identifying patients with clinically important pain.
Pearls for Practice
Advantages of the NRS for pain screening are it is short, easy to administer, and is validated as a measure of intensity of pain in populations with known pain.
Compared with measures of functional interference and reason for a visit to the physician, the NRS has moderate accuracy.