ARTHRITIS & RHEUMATISM
Vol. 60, No. 10, October 2009, pp 2855–2857
DOI 10.1002/art.24858
© 2009, American College of Rheumatology
Arthritis & Rheumatism
An Official Journal of the American College of Rheumatology
www.arthritisrheum.org and www.interscience.wiley.com
EDITORIAL
Diagnosing Acute Nonspecific Low Back Pain: Time to Lower the Red Flags?
Martin Underwood
1.7%). The incidence of spinal fractures (8 [0.7%] of
1,172 patients [95% CI 0.4–1.3%]) and malignancy
(none of 1,172 patients [95% CI 0–0.3%]) was much
lower than the commonly quoted values for osteoporotic
fractures and malignancy (⬃4% and ⬃0.7%, respectively) (7).
An important strength of this study is that data
were collected from members of different health professions who provide first-contact care for acute back pain
in a primary care setting. This approach also results in an
important weakness of the study: only first presentations
for a new episode of low back pain were considered.
Serious disorders causing low back pain are likely to be
more common in some other patient groups. Persons in
such groups include those presenting for a second, third,
or subsequent primary care consultation because of pain
that is not resolving, those presenting to an emergency
room, and those who had been referred for specialist care.
Thus, even though the incidence of serious disease is very low at the time of first consultations for new
episodes of acute low back pain, clinicians do need to
keep their diagnosis of nonspecific low back pain under
review during the subacute and early chronic phases of
low back pain (8). Indeed, these serious disorders can
develop in patients with established disabling chronic low
back pain and thus cannot be disregarded regardless of
how long the patient has been experiencing low back pain.
With this extremely low incidence of serious
disease identified following a first consultation for a new
episode of acute low back pain, the large number of
patients with 1 or more red flag symptoms (80%) is of
considerable concern. If nearly everyone with acute low
back pain has a red flag, then the presence of a red flag
will not help the clinician in deciding whether any
further investigation or treatment is needed. Nearly all
of the individual red flag questions were uninformative.
The only diagnostic decision rule that Henschke and
Episodes of acute low back pain are a universal
human experience (1). Usually, this is a benign, selflimiting disorder that does not require professional
advice or specific treatment (2). Once someone with
acute low back pain presents for care, a plethora of
management guidelines are available to treating clinicians. These guidelines typically recommend that serious
disorders (cauda equina syndrome, fracture, infection,
inflammatory disorders, malignancy) should be excluded, using a number of “red flag” questions, before
making a diagnosis of nonspecific low back pain (3). In
contrast to the high-quality data available for at least
some treatments of nonspecific low back pain, systematic reviews of the use of red flag questions to identify
malignancy and fractures show that the strength of the
evidence underpinning these screening questions is weak
(4,5). Furthermore, few of the data that are available
were collected in a primary care setting, where most
consultations for back pain take place.
In this issue of Arthritis & Rheumatism, Henscke
and colleagues report on the performance of commonly
recommended red flags in a prospective study of 1,172
consecutive patients presenting to a primary care setting
because of acute low back pain (duration of ⬎24 hours
but ⬍6 weeks) (6). After careful followup over 1 year, a
serious cause for back pain was identified in only 11
patients (0.9%; 95% confidence interval [95% CI] 0.5–
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 NICE
guidelines on early management of persistent nonspecific low back
pain.
Address correspondence and reprint requests to Martin Underwood, 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 revised
form June 29, 2009.
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colleagues could generate was for fracture (positive
response for 3 of 4 factors, female sex, age ⬎70 years,
prolonged use of corticosteroids, and significant
trauma), which had a high positive likelihood ratio of
218. This was not, however, substantially different from
the positive likelihood ratio of 194 for a clinical diagnosis made by clinicians without using a formalized diagnostic decision rule. This resonates with the observation
that screening tools for psychosocial “yellow flags,”
designed to identify people with nonspecific low back
pain with a poor prognosis, did not perform substantially
better than clinical judgment (9).
Any recommendations for the use of red flags
need to consider how likely it is that patients who are
seen in primary care will have a serious disorder causing
their low back pain and the consequences if the diagnosis is overlooked.
Cauda equina syndrome due to disc prolapse can
have catastrophic consequences, and early diagnosis and
surgical treatment are probably helpful (10). However,
the incidence of cauda equina syndrome is so low that
most general (family) practitioners in the UK will not
see a true case in their practicing lifetime (10). The
clinical diagnosis of cauda equina syndrome is difficult,
with a false-positive rate of 43% even when the diagnosis
is made by experienced clinicians (10). There is a need to
be vigilant for the new onset of perianal sensory change
or bladder symptoms in patients with low back pain of
any duration, with a low threshold for referral for expert
assessment (10). However, this vigilance needs to be
tempered by the reality that many of us who work in
primary care will never see a case of cauda equina
syndrome.
Osteoporotic fractures of the spine are a relatively
common presentation in primary care but represent
⬍1% of the presentations in the study by Henschke and
colleagues (6). Clinician judgment, however, has a positive predictive value similar to that of the formulaic red
flag–based diagnostic rule (6). In cases of acute back
pain, appropriate management for most patients will be
pain relief and resumption of normal activities as soon as
possible; such an approach is similar to the management
of nonspecific low back pain. In the absence of convincing evidence that vertebroplasty or kyphoplast are superior to medical management, there is little need for
urgent investigation and referral to specialists (11).
Diagnosing and treating osteoporosis to prevent further
fractures are important, and possibly more important
than diagnosing the fracture itself, in persons at risk of a
fragility fracture. In my opinion, there is little point in
doing further investigations for most patients with
UNDERWOOD
known osteoporosis who present with a new episode of
low back pain.
Infections may account for 0.01% of cases of low
back pain (7). It is hardly surprising that Henschke et al
did not identify any cases of infection in their study of
only 1,172 patients, even though reasonable numbers
had positive responses for the red flags suggested to
screen for infection (6). In practical terms, this means
that spinal infection as a cause of low back pain will, like
cauda equina syndrome, be a once-in-a-lifetime diagnosis for most practitioners working in primary care.
Nearly 3% of patients with acute low back pain have the
commonest red flag for infection (constant, progressive
nonmechanical pain) at the time of their first consultation (6). There is a need to be vigilant for the patient
with deteriorating back pain who is systemically unwell,
but this vigilance needs to be tempered by knowledge of
the rarity of spinal infections.
Ankylosing spondylitis and other inflammatory disorders are an uncommon cause of low back pain. These
are chronic disorders, the diagnosis of which is commonly delayed for several years. What is less clear is
whether the majority of patients with mild disease are
harmed by this delay, because many will be treated with
nonsteroidal antiinflammatory drugs and advised to
exercise irrespective of the diagnosis. In primary care
patients with chronic low back pain, established ankylosing spondylitis with unequivocal radiographic change
is rare, although using wider diagnostic criteria for an
axial spondylarthropathy, the prevalence may be as high
as 5% (12). The risk here from the use of red flags is
swamping of secondary care services, because of the
high number of false-positive results for the screening
questions. Three of the screening questions used by
Henschke and colleagues had positive replies from more
than one-fourth of the patients; these patients represent
a population with acute pain who would not at first
presentation satisfy any diagnostic criteria for an axial
spondylarthropathy. The possibility of ankylosing spondylitis as a diagnosis needs to be considered, but only in
patients who are not experiencing improvement after
more than 3 months.
Malignancy is a diagnosis that practitioners would
not wish to miss. It is reassuring that none of the 46
patients with a past history of cancer in the Henschke
study had malignancy as a cause of their back pain (6).
The formulaic use of a red flag of a past history of cancer
is too blunt an instrument to be used in routine practice
without considering the type of cancer and how long ago
it was diagnosed. Except in the context that a cancer is
being, or has recently been, treated, clinician judgment is
EDITORIAL
needed to decide which cases may need further investigation. In cases of increasing pain or failure to improve,
malignancy needs to be considered, because it may be
that it is at the second or third consultation (not studied
by Henschke) when malignancy needs to be primarily
considered.
Too great a focus on addressing red flag questions may distract the clinician from delivering key
information to the patient: reassurance as to the benign
nature of the disorder for the vast majority of patients
and the benefits of avoiding bed rest and maintaining
normal activity, including work. It is worrying that some
investigators are advocating comprehensive recording of
answers to all red flag questions as a desirable aspiration
in back pain management (13). The indiscriminate use
of red flag symptoms as a trigger to order further
investigations will lead to unnecessary investigations that
are themselves harmful, through a combination of overmedicalizing a benign usually self-limiting disorder, the
harmful effects of radiation from obtaining unnecessary
radiographs and computed tomography scans, and the
consequences of these investigations themselves producing false-positive results.
That factors known to be associated with a specific diagnosis were not found to be helpful in this study
might appear surprising. It is important to recognize that
a statistically significant association between a screening
tool and the condition of interest does not mean that its
positive and negative predictive values in any particular
population is sufficient to justify its use in clinical
practice (14). It is tempting to call for further research to
determine which patients to investigate for specific
causes of low back pain in different populations. However, any study with sufficient statistical power to produce robust estimates of the sensitivity and specificity of
single and multiple variables, which can then be used to
produce positive and negative predictive values in different populations, is likely to be many times larger than
this current study. It may be difficult to persuade
research funders that this is good use of resources.
Few people will come to significant harm if the
diagnosis of a serious cause for their back pain is delayed
for a moderate period of time. Taking this and the poor
performance of red flags used to identify people with
specific causes for their back pain into consideration, we
should refocus our attention away from recording an
exhaustive list of red flags to considering a small number
of disorders in which early diagnosis and treatment
might make a big difference, and use time as a diagnostic
tool for the remainder. Specifically, we should consider
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cauda equina syndrome, major intraabdominal pathology, focal infections, and fractures. If, in the clinician’s
judgment, the patient may have one of these, then
appropriate investigation and treatment are needed.
This judgment may need to be informed by combining
multiple observations, perhaps made over 1 or more
consultation. Because we do not have enough data to
create formal decision rules, this needs to rely on the
skills and experience of the treating clinician. This
approach, which is grounded in considering the clinical
features of disorders of interest, is likely to be more
discriminatory than formulaic application of red flags
and decision rules.
ACKNOWLEDGMENTS
I am grateful to Shilpa Patel, Dawn Carnes, and David
Evans for their comments on earlier versions of this article.
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