ARTHRITIS & RHEUMATISMVol. 60, No. 10, October 2009, pp 2855–2857DOI 10.1002/art.24858© 2009, American College of Rheumatology

EDITORIAL

Diagnosing Acute Nonspecific Low Back Pain: Time to Lower the Red Flags?

Martin Underwood

Episodes of acute low back pain are a universalhuman experience (1). Usually, this is a benign, self-limiting disorder that does not require professionaladvice or specific treatment (2). Once someone withacute low back pain presents for care, a plethora ofmanagement guidelines are available to treating clini-cians. These guidelines typically recommend that seriousdisorders (cauda equina syndrome, fracture, infection,inflammatory disorders, malignancy) should be ex-cluded, using a number of “red flag” questions, beforemaking a diagnosis of nonspecific low back pain (3). Incontrast to the high-quality data available for at leastsome treatments of nonspecific low back pain, system-atic reviews of the use of red flag questions to identifymalignancy and fractures show that the strength of theevidence underpinning these screening questions is weak(4,5). Furthermore, few of the data that are availablewere collected in a primary care setting, where mostconsultations for back pain take place.

In this issue of Arthritis & Rheumatism, Hensckeand colleagues report on the performance of commonlyrecommended red flags in a prospective study of 1,172consecutive patients presenting to a primary care settingbecause of acute low back pain (duration of �24 hoursbut �6 weeks) (6). After careful followup over 1 year, aserious cause for back pain was identified in only 11patients (0.9%; 95% confidence interval [95% CI] 0.5–

1.7%). The incidence of spinal fractures (8 [0.7%] of1,172 patients [95% CI 0.4–1.3%]) and malignancy(none of 1,172 patients [95% CI 0–0.3%]) was muchlower than the commonly quoted values for osteoporoticfractures and malignancy (�4% and �0.7%, respec-tively) (7).

An important strength of this study is that datawere collected from members of different health profes-sions who provide first-contact care for acute back painin a primary care setting. This approach also results in animportant weakness of the study: only first presentationsfor a new episode of low back pain were considered.Serious disorders causing low back pain are likely to bemore common in some other patient groups. Persons insuch groups include those presenting for a second, third,or subsequent primary care consultation because of painthat is not resolving, those presenting to an emergencyroom, and those who had been referred for specialist care.

Thus, even though the incidence of serious dis-ease is very low at the time of first consultations for newepisodes of acute low back pain, clinicians do need tokeep their diagnosis of nonspecific low back pain underreview during the subacute and early chronic phases oflow back pain (8). Indeed, these serious disorders candevelop in patients with established disabling chronic lowback pain and thus cannot be disregarded regardless ofhow long the patient has been experiencing low back pain.

With this extremely low incidence of seriousdisease identified following a first consultation for a newepisode of acute low back pain, the large number ofpatients with 1 or more red flag symptoms (80%) is ofconsiderable concern. If nearly everyone with acute lowback pain has a red flag, then the presence of a red flagwill not help the clinician in deciding whether anyfurther investigation or treatment is needed. Nearly allof the individual red flag questions were uninformative.The only diagnostic decision rule that Henschke and

Martin Underwood, MD, FRCGP, University of Warwick,Coventry, UK.

Professor Underwood has received honoraria (less than$10,000) from the National Institute of Health and Clinical Excellence(NICE) for service as Chair of the group that developed NICEguidelines on early management of persistent nonspecific low backpain.

Address correspondence and reprint requests to Martin Un-derwood, MD, FRCGP, Warwick Medical School Clinical Trials Unit,University of Warwick, Gibbett Hill Road, Coventry CV4 7AL, UK.E-mail: m.underwood@warwick.ac.uk.

Submitted for publication May 6, 2009; accepted in revisedform June 29, 2009.

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colleagues could generate was for fracture (positiveresponse for 3 of 4 factors, female sex, age �70 years,prolonged use of corticosteroids, and significanttrauma), which had a high positive likelihood ratio of218. This was not, however, substantially different fromthe positive likelihood ratio of 194 for a clinical diagno-sis made by clinicians without using a formalized diag-nostic decision rule. This resonates with the observationthat screening tools for psychosocial “yellow flags,”designed to identify people with nonspecific low backpain with a poor prognosis, did not perform substantiallybetter than clinical judgment (9).

Any recommendations for the use of red flagsneed to consider how likely it is that patients who areseen in primary care will have a serious disorder causingtheir low back pain and the consequences if the diagno-sis is overlooked.

Cauda equina syndrome due to disc prolapse canhave catastrophic consequences, and early diagnosis andsurgical treatment are probably helpful (10). However,the incidence of cauda equina syndrome is so low thatmost general (family) practitioners in the UK will notsee a true case in their practicing lifetime (10). Theclinical diagnosis of cauda equina syndrome is difficult,with a false-positive rate of 43% even when the diagnosisis made by experienced clinicians (10). There is a need tobe vigilant for the new onset of perianal sensory changeor bladder symptoms in patients with low back pain ofany duration, with a low threshold for referral for expertassessment (10). However, this vigilance needs to betempered by the reality that many of us who work inprimary care will never see a case of cauda equinasyndrome.

Osteoporotic fractures of the spine are a relativelycommon presentation in primary care but represent�1% of the presentations in the study by Henschke andcolleagues (6). Clinician judgment, however, has a pos-itive predictive value similar to that of the formulaic redflag–based diagnostic rule (6). In cases of acute backpain, appropriate management for most patients will bepain relief and resumption of normal activities as soon aspossible; such an approach is similar to the managementof nonspecific low back pain. In the absence of convinc-ing evidence that vertebroplasty or kyphoplast are supe-rior to medical management, there is little need forurgent investigation and referral to specialists (11).Diagnosing and treating osteoporosis to prevent furtherfractures are important, and possibly more importantthan diagnosing the fracture itself, in persons at risk of afragility fracture. In my opinion, there is little point indoing further investigations for most patients with

known osteoporosis who present with a new episode oflow back pain.

Infections may account for 0.01% of cases of lowback pain (7). It is hardly surprising that Henschke et aldid not identify any cases of infection in their study ofonly 1,172 patients, even though reasonable numbershad positive responses for the red flags suggested toscreen for infection (6). In practical terms, this meansthat spinal infection as a cause of low back pain will, likecauda equina syndrome, be a once-in-a-lifetime diagno-sis for most practitioners working in primary care.Nearly 3% of patients with acute low back pain have thecommonest red flag for infection (constant, progressivenonmechanical pain) at the time of their first consulta-tion (6). There is a need to be vigilant for the patientwith deteriorating back pain who is systemically unwell,but this vigilance needs to be tempered by knowledge ofthe rarity of spinal infections.

Ankylosing spondylitis and other inflammatory dis-orders are an uncommon cause of low back pain. Theseare chronic disorders, the diagnosis of which is com-monly delayed for several years. What is less clear iswhether the majority of patients with mild disease areharmed by this delay, because many will be treated withnonsteroidal antiinflammatory drugs and advised toexercise irrespective of the diagnosis. In primary carepatients with chronic low back pain, established anky-losing spondylitis with unequivocal radiographic changeis rare, although using wider diagnostic criteria for anaxial spondylarthropathy, the prevalence may be as highas 5% (12). The risk here from the use of red flags isswamping of secondary care services, because of thehigh number of false-positive results for the screeningquestions. Three of the screening questions used byHenschke and colleagues had positive replies from morethan one-fourth of the patients; these patients representa population with acute pain who would not at firstpresentation satisfy any diagnostic criteria for an axialspondylarthropathy. The possibility of ankylosing spon-dylitis as a diagnosis needs to be considered, but only inpatients who are not experiencing improvement aftermore than 3 months.

Malignancy is a diagnosis that practitioners wouldnot wish to miss. It is reassuring that none of the 46patients with a past history of cancer in the Henschkestudy had malignancy as a cause of their back pain (6).The formulaic use of a red flag of a past history of canceris too blunt an instrument to be used in routine practicewithout considering the type of cancer and how long agoit was diagnosed. Except in the context that a cancer isbeing, or has recently been, treated, clinician judgment is

2856 UNDERWOOD

needed to decide which cases may need further investi-gation. In cases of increasing pain or failure to improve,malignancy needs to be considered, because it may bethat it is at the second or third consultation (not studiedby Henschke) when malignancy needs to be primarilyconsidered.

Too great a focus on addressing red flag ques-tions may distract the clinician from delivering keyinformation to the patient: reassurance as to the benignnature of the disorder for the vast majority of patientsand the benefits of avoiding bed rest and maintainingnormal activity, including work. It is worrying that someinvestigators are advocating comprehensive recording ofanswers to all red flag questions as a desirable aspirationin back pain management (13). The indiscriminate useof red flag symptoms as a trigger to order furtherinvestigations will lead to unnecessary investigations thatare themselves harmful, through a combination of over-medicalizing a benign usually self-limiting disorder, theharmful effects of radiation from obtaining unnecessaryradiographs and computed tomography scans, and theconsequences of these investigations themselves produc-ing false-positive results.

That factors known to be associated with a spe-cific diagnosis were not found to be helpful in this studymight appear surprising. It is important to recognize thata statistically significant association between a screeningtool and the condition of interest does not mean that itspositive and negative predictive values in any particularpopulation is sufficient to justify its use in clinicalpractice (14). It is tempting to call for further research todetermine which patients to investigate for specificcauses of low back pain in different populations. How-ever, any study with sufficient statistical power to pro-duce robust estimates of the sensitivity and specificity ofsingle and multiple variables, which can then be used toproduce positive and negative predictive values in dif-ferent populations, is likely to be many times larger thanthis current study. It may be difficult to persuaderesearch funders that this is good use of resources.

Few people will come to significant harm if thediagnosis of a serious cause for their back pain is delayedfor a moderate period of time. Taking this and the poorperformance of red flags used to identify people withspecific causes for their back pain into consideration, weshould refocus our attention away from recording anexhaustive list of red flags to considering a small numberof disorders in which early diagnosis and treatmentmight make a big difference, and use time as a diagnostictool for the remainder. Specifically, we should consider

cauda equina syndrome, major intraabdominal pathol-ogy, focal infections, and fractures. If, in the clinician’sjudgment, the patient may have one of these, thenappropriate investigation and treatment are needed.This judgment may need to be informed by combiningmultiple observations, perhaps made over 1 or moreconsultation. Because we do not have enough data tocreate formal decision rules, this needs to rely on theskills and experience of the treating clinician. Thisapproach, which is grounded in considering the clinicalfeatures of disorders of interest, is likely to be morediscriminatory than formulaic application of red flagsand decision rules.

ACKNOWLEDGMENTS

I am grateful to Shilpa Patel, Dawn Carnes, and DavidEvans for their comments on earlier versions of this article.

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