Positive responses to "red flag" screening questions for back pain warranted further investigation, though the positive predictive value was poor. Negative responses to screening "red flag" questions were useless as a screening tool for ruling out serious disease, such as fracture, infection, malignancy, or cauda equina.
Why does this matter?
We are trained to ask the "red flag" questions about back pain: bowel or bladder incontinence, trauma, fever, IV drug abuse, nocturnal pain, history of cancer, etc. But how effective is it to ask these questions as a screening tool for serious back pathology?
Red flags fading
This was a retrospective review of 9940 patients being evaluated for back pain who completed a questionnaire that asked the "red flag" questions about their pain. They followed up the final diagnoses and imaging that flowed from this first visit. "Red flag" diagnoses included: vertebral fracture, malignancy, infection, or cauda equina syndrome. Overall, they found positive responses were weak diagnostic predictors of a red flag diagnosis; 9.31 was the best positive likelihood ratio (PLR). Most PLR were 1 to 2, which means they were largely useless for increasing the post-questionnaire probability of disease. Combinations of variables were somewhat better at predicting who had disease but not which patients did not. Examples were: age > 50 + history of trauma (PLR 2.54); unexplained weight loss + history of cancer (PLR 10.25); fever, chills and sweating + recent infection (PLR 13.15).
No single question was a meaningful negative predictor of disease. Red flag questions had sensitivities hovering 20% with NLR around 0.9. What this means is if a patient answers affirmatively to "red flag" questions, it warrants further investigation. But serious diagnoses of fracture, infection, malignancy, and cauda equina were not "ruled out" by asking screening questions.
Red Flags for Low Back Pain Are Not Always Really Red: A Prospective Evaluation of the Clinical Utility of Commonly Used Screening Questions for Low Back Pain. J Bone Joint Surg Am. 2018 Mar 7;100(5):368-374. doi: 10.2106/JBJS.17.00134.
Editorial: Should We Still Use Red Flags in the Diagnosis of Low Back Pain?: Commentary on an article by Ajay Premkumar, MD, MPH, et al.: "Red Flags for Low Back Pain Are Not Always Really Red. A Prospective Evaluation of the Clinical Utility of Commonly Used Screening Questions for Low Back Pain". J Bone Joint Surg Am. 2018 Mar 7;100(5):e31. doi: 10.2106/JBJS.17.01391.
Peer reviewed by Thomas Davis