STUDY QUESTION What are the best red flags to indicate the possibility of fracture or malignancy in patients presenting with low back pain in primary, secondary, or tertiary care?
SUMMARY ANSWER Older age, prolonged corticosteroid use, severe trauma, and presence of a contusion or abrasion increase the likelihood of spinal fracture (likelihood was higher with multiple red flags); a history of malignancy increases the likelihood of spinal malignancy.
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Selection criteria for studies
Medline, OldMedline, Embase, and CINAHL were searched from earliest available up to 1 October 2013. Primary diagnostic studies comparing red flags for fracture or malignancy to an acceptable reference standard in any language were included. Three independent reviewers extracted data from qualifying studies and assessed quality with QUADAS.
We generated diagnostic accuracy statistics and post-test probabilities for each red flag identified and matched these to guideline recommendations for the use of red flags involving the diagnosis of low back pain.
We included 14 studies (eight from primary care, two from secondary care, four from tertiary care) evaluating 53 red flags; only five studies evaluated combinations of red flags. Pooling of data was not possible because of index test heterogeneity. Study quality items that were often inadequately covered or unclear were an acceptable delay between index and reference tests, partial verification, differential verification, reference standard blinding, reporting uninterpretable results, and explaining withdrawals. Point prevalence we used to calculate post-test probability was determined by extracting prevalence from a reduced set of methodologically robust studies for fracture and cancer and by considering a value that could be readily applied in the clinical setting (fracture: 1% for primary care, 5% for secondary and tertiary care; malignancy: 0.5% for primary care, 1.5% for secondary and tertiary care). Many red flags in current guidelines provide virtually no change in probability of fracture. Example post-test probabilities are spinal tenderness (2%, 95% confidence interval 1% to 3%) and spasm (1%, 0% to 4%). The red flags with the highest post-test probability for detection of fracture were older age (9%, 95% confidence interval 3% to 25%), prolonged corticosteroid use (33%, 10% to 67%), severe trauma (11%, 8% to 16%), and presence of a contusion or abrasion (62%, 49% to 74%). The probability of spinal fracture was higher when multiple red flags were present (90%, 34% to 99%); but this approach is not endorsed in current guidelines. Many red flags in current guidelines provide little or virtually no change in probability of malignancy. Examples are unexplained weight loss (1%, 95% confidence interval 0% to 5%), insidious onset (1%, 0% to 1%), and failure to improve after one month (2%, 1% to 3%). The red flag with the highest post-test probability for detection of spinal malignancy was history of malignancy (33%, 22% to 46%).⇓
Bias, confounding, and other reasons for caution
In this review we graphically portray the post-test probability and 95% confidence intervals for investigated red flags. Our results enable clinicians to easily interpret the informativeness of red flags to screen for spinal fracture and malignancy. A limitation of this approach is that prevalence of fracture and malignancy varied considerably between studies (fracture: from 0.7% to 11.0%; malignancy: from 0% to 7.0%) and depended on study methods and setting. Therefore values for prevalence and post-test probability in our review might not generalise to every setting.
This is a summary of a paper that was published on bmj.com as BMJ 2013;347:f7095
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