Journal of Orthopaedic & Sports Physical Therapy
Official Publication of the Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association
The Use of Patient Symptoms to Screen for
Serious Back Problems
Kathryn E. Roach, PhD, PT'
Mark Brown, M D, PhD *
Elizabeth Ricker, MS, P T ~
Peter Ahenburger, MS, PT
lanet Tompkins, RN5
L
ow back pain is a broad
diagnosis encompassing a
wide variety of disorders
which differ greatly in
etiology, prognosis, and
appropriate management. The actual
cause of low back pain can range
from musculoligamentous injuries to
anatomic abnormalities or even underlying systemic diseases (2). It is
estimated that some form of low back
pain will affect 80% of all Americans
at some time during their lives (5).
Of this group, most will recover from
the initial episode but will suffer frequent recurrences during their lifetime.
Patients with low back pain now
have direct access to physical therapy
without a physician's referral in 22
states. Even when a patient is referred by a physician, the physical
therapist must remain alert to the
possibility that the patient may require medical care outside the realm
of physical therapy. Physical therapists must be able to screen low back
pain patients to identify serious low
back problems that require additional diagnostic evaluation and treatment by a physician.
Screening is a procedure used to
identify groups of individuals who
would benefit from some type of
medical attention. The Commission
on Chronic Illness (1) defined
screening as ". . . the presumptive
identification of unrecognized disease
Even when a patient is referred by a physician, the physical therapist must remain alert to the
possibility that the patient may require medical care outside the realm of physical therapy. Physical
therapists must be able to screen low back pain patients to identify those who have serious low back
problems which require additional diagnostic evaluation and treatment by a physician. It is
important for physical therapists to know which symptoms and signs or combination of symptoms
and signs best indicate the likelihood of a serious problem. The purpose of this study was to test the
sensitivity and specificity of low back pain symptoms in distinguishing individuals with a benign low
back problem from those requiring surgical or medical intervention. Demographic and clinical data
were collected retrospectively from a standardized low back pain questionnaire located in the
medical records of 174 low back pain patients. Patients were classified as having a benign low back
problem (N = 4 1) or a serious low back problem (N = 133) based on surgical findings or long term
follow-up. Some individual symptoms had high specificity, but none had high sensitivity. To improve
sensitivity while attempting to maintain moderate specificity, a number of symptoms were
considered in parallel. The highest combination of sensitivity (.87) and specificity (.SO)was obtained
by combining in parallel the symptoms of unable to sleep, awakened and unable to fall back to
sleep, medication required to sleep, and pain worsened by walking.
Key Words: screening, low back pain, clinical decision-making
'Assistant Professor, Division of Physical Therapy, Department of Orthopaedics and Rehabilitation, University
of Miami School of Medicine, 5915 Ponce de Leon Blvd., Plumer Building, 5th Floor, Coral Gables, FL 33146
'Professor and Chair, Department of Orthopaedics and Rehabilitation, University of Miami School of Medicine,
Coral Gables, FL
'Staff Physical Therapist, St. loseph's Care Center, Phoenix, AZ
4Staff Physical Therapist, Novacare Valley of the Sun Rehabilitation Hospital, Glendale, AZ
SClinical Research Nurse, Department of Orthopaedics and Rehabilitation, University of Miami School of Medicine, Coral Gables, FL
or defect by the application of tests,
examinations, or other procedures
which can be applied rapidly to sort
out apparently well persons who
probably have the disease from those
who probably do not. A screening
test is not intended to be diagnostic.
Persons with positive or suspicious
findings must be referred to their
physicians for diagnosis and necessary
treatment." In the case of low back
pain, screening is done to identify
patients with a high probability of
having low back problems that are
serious and will require additional
diagnostic and treatment procedures
that are outside the realm of physical
therapy practice. Since physical therapists do not generally employ radiologic or laboratory testing, screening
by physical therapists for serious low
back pain must be based primarily on
patient symptoms and signs. Therefore, it is important for physical therVolume 21 e Number 1 e January 1995 e JOSPT
RESEARCH
apists to know which symptoms, signs,
or combination of symptoms and
signs best indicate the likelihood of a
serious problem. The validity of a
screening test is determined by its
sensitivity and specificity. Sensitivity is
the ability of a test to correctly identify subjects who have disease, and
specificity is defined as the ability of
a test to correctly identify those who
do not have disease (4,6). Although a
number of physical therapy texts propose screening criteria to identify low
back pain patients who have serious
underlying disorders, these sources
fail to provide information on the
sensitivity or specificity of the criteria
they advocate (3,7).
Deyo et a1 review addressed the accuracy of various symptoms and signs in
distinguishing between benign and
serious low back problems.
Although patient signs elicited
during the physical examination almost certainly have an important role
in screening for serious low back
pain, this study was limited to an examination of patient symptoms. The
purpose of this study was to determine the sensitivity and specificity of
patient-reported symptoms in distinguishing individuals with benign low
back problems from those who require surgical or other medical intervention outside the realm of physical
therapy.
STUDY
quate number of subjects within each
of the categories of serious low back
problems, these categories were intentionally oversampled so that the
final cohort included 133 subjects
with serious low back problems and
41 subjects with benign low back
problems. Subjects whose histories
involved possible substance abuse or
litigation or any psychogenic behavior noted during evaluation were excluded due to potential symptom
magnification. Although these s u b
jects may have had an organic problem, symptom magnification during
self-reporting would make the validity
of the data questionable (9).
Procedure
It is imporfant for
physical therapists to
know which
symptoms, signs, or
combination of
symptoms and signs
best indicate the
likelihood of a
serious problem.
Deyo et al (2) compiled findings
from a number of sources on the
sensitivity and specificity of various
elements of the patient history and
physical examination in diagnosing
serious low back disorders such as
cancer, spinal stenosis, herniated
disc, and compression fracture. They
found that items such as previous
history of cancer, unexplained weight
loss, and failure to improve with a
month of therapy all had specificities
above .90 for the detection of cancer.
Unfortunately, none of these items
had a sensitivity above .35, indicating
that many low back patients with cancer did not report these symptoms.
None of the studies reported in the
JOSPT Volume 21 Number 1 January 1995
METHODS
Design
A retrospective medical record
review was conducted to determine
the low back pain symptoms and demographic characteristics of a cohort
of patients who presented to a tertiary referral outpatient orthopaedic
clinic of a large teaching hospital for
treatment of low back pain. Each subject's low back diagnosis was recorded and classified as either benign or serious (Table 1). All
diagnoses were confirmed surgically
or by long-term follow-up.
Subjects
The medical records of 174 subjects were selected for this study.
Records were selected for inclusion
in this study based on the availability
of a completed intake questionnaire
and a confirmed low back pain diagnosis. In order to include an ade-
The medical records of all s u b
jects contained a standardized, selfadministered intake questionnaire
which was completed at the time of
the first clinic visit. The questionnaire included demographic and selfreported symptoms, such as sleep
disturbances related to low back pain,
changes in bowel and bladder function, and presence of low Sack pain
when performing activities such as
walking, driving, pushing, sitting, or
standing. Information from this standardized intake questionnaire was
transferred, without modification or
interpretation, to a data collection
form which wa.. identified only by a
unique code number. Demographic
information and patient final diagne
sis were abstracted from the medical
record.
Data Analysis
Student's t test and chi square
statistics were calculated to compare
Benign back pain
Low back pain that has a benign, self-limiting course not requiring
surgery or other aggressive medical treatment.
Serious back pain
Low back pain attributable to spinal abnormalities requiring surgery or
low back pain secondary to another underlying disorder. This
category includes spinal stenosis or herniated disk requiring surgery,
osteoporotic fracture, tumor, and infection.
TABLE 1. Low back pain classifications.
3
RESEARCH
STUDY
the demographic characteristics of
serious low back problem subjects to
those with benign low back problems.
The sensitivity and specificity of individual symptoms in distinguishing
serious low back problems from benign low back problems were calculated. Sensitivity is defined as the p r e
portion of individuals who have a
disease and test positive for that disease using a screening instrument
(4). For the purposes of this study,
the sensitivity of an item indicated
the proportion of subjects with serious low back problems who reported
the presence of a symptom. Sensitivity was calculated by dividing the
number of patients with serious low
Specificity was the
probability of
responding negatively
to an item if a subject
had a benign low back
problem instead of a
serious low
back problem.
back problems who reported a specific symptom by the total number of
patients with serious low back pain.
Therefore, the higher the sensitivity
of the symptom, the lower the p r e
portion of subjects with serious low
back problems who were classified as
having benign low back problems
(false negatives) based on the presence of that symptom (Table 2). It is
important to note that sensitivity only
provides information about patients
with serious low back problems. Specificity is defined as the proportion of
individuals who do not have a disease
and test negative for that disease using a screening instrument (4).
Therefore, in this study, specificity
Serious Low
Back Problem
Benign Low
Back Problem
Total
Symptom present
(test positive)
(a)
True positive
0
False positive
(a + b)
All subjects who test
positive
Symptom absent
(test negative)
(c)
False negative
(dl
True negative
(C + d)
All subjects who test
negative
Total
(a + C)
All subjects with
a serious back
problem
(b + d)
All subjects with a
benign back
problem
(atbtctd)
All subjects
Sensitivity = True positive + all subjects with a serious back problem.
Specificity = True negative + all subjects with a benign back problem.
TABLE 2. Sensitivity and specificify.
was the probability of responding
negatively to an item if a subject had
a benign low back problem instead of
a serious low back problem. Specificity was calculated by dividing the
number of subjects with benign low
back problems who did not report a
symptom by the total number of s u b
jects with benign low back problems.
Specificity only provides information
about subjects with benign low back
problems. A test with high specificity
would not classify benign low back
problems as serious low back p r o b
lems (false positive). An ideal screening test has both a high sensitivity
and a high specificity.
As a strategy to improve sensitivity, various combinations of symp
toms were considered in parallel.
Screening in parallel entails the decision to classify a subject as screening
positive if that subject reports any
one of a group of symptoms (4). The
sensitivity and specificity of various
combinations of symptoms were also
calculated. For screening in parallel,
sensitivity was calculated by dividing
the number of patients with serious
low back problems who reported any
one of the group of symptoms by the
total number of subjects with serious
low back pain. Specificity was calculated by dividing the number of s u b
jects with benign low back problems
who did not report any of the group
of symptoms by the total number of
subjects with benign low back p r o b
lems. Data analysis was conducted
using the SAS program (version 6.01,
SAS Institute, Cary, NC) (8) on a
VAX mainframe computer.
RESULTS
Subjects in the benign low back
problem and serious low back p r o b
lem groups were similar in height,
weight, and gender distribution.
However, the mean age of the serious
low back problem group was 54.38
years compared with 42.68 years for
the benign low back problem group
(Table 3). The specificity and sensitivity calculated for each item are
presented in Table 4. Items 4, 5, 6, 8,
9, and 10 demonstrated high specificity but low sensitivity, while items 3,
7, 11, and 13 demonstrated moderate
sensitivity with moderate to low specificity. Items with moderate sensitivity
and specificity, such as 7, generated a
fairly large number of false positive
and false negative findings (Table 5).
No individual symptoms had high
sensitivity.
Combining symptoms in parallel
increased sensitivity but substantially
decreased specificity (Table 6). Combination 7 had the highest sensitivity
but had very low specificity. Combination 5 had the highest combined sensitivity and specificity. This combination produced very few false negative
findings (Table 7).
Volume 21 Number 1 January 1995 JOSPT
-... -.-
-
.-.--- ---.
-..
-.
."
..
. . . .-
Characteristic
Serious Low Back
Problem ( N = 133)
Age
Weight
Height
Proportion male
54.38
157.1 1
66.77
50.25
. . -. .
.-
.
.. . .
.
.
Benign Low Back
Problem ( N = 41)
- -. . ..
- .-
.
* Student's t test.
t Chi square.
TABLE 3. Subject demographic characteristics.
Symptom
Sensitii
Specificity
TABLE 4. Sensitivity and specificity of individual symptoms.
Serious Low
Back Problem
Benign Low
Back Problem
Symptom present
(test positive)
99
16
True positive
False positive
Symptom absent
(test negative)
False negative
33
24
True negative
Total
.
..
.S T U D Y
,
.
. ..
DISCUSSION
p value
1. Pain worse in AM
2. Pain worse in PM
3. Pain is constant
4. Unable to urinate
5. Can't hold urine
6. Currently smoke
7. Walking aggravates pain
8. Pain wakes from sleep
9. Need sleep medications
10. Unable to sleep
11. Sitting aggravates pain
12. Driving aggravates pain
13. Bending aggravates pain
RESEARCH
- - .- .- .
.- . . -. .
-
Although the ideal screening test
would be 100% sensitive and 100%
specific, sensitivity and specificity are
usually inversely related. This principle is demonstrated by the findings
of this study. A number of symptoms
had very high specificity but low sensitivity. If there must be a tradeaff
between the sensitivity and specificity
of a screening test, then it is important to emphasize the characteristic
that is most important for a given
clinical problem. The relative importance of sensitivity and specificity may
differ depending on the disease or
condition involved. If the diagnostic
tests required to confirm a diagnosis
The combination of
symvtoms that
includes the three
sleep disturbance
symptoms and pain
worsened by walking
has a sensitivity of .87.
Sensitivity: 99/132 = 2 5 .
Specificity: 24/40 = .60.
TABLE 5. Sensitivity and specificity o f walking aggravates low back pain.
SPP~W
1. Sleep problems*
2. Sleep problems*
Sensitivity
Specificity
.50
.75
-85
.27
.76
.53
.77
.20
.87
.50
.92
.27
.98
.05
Pain worse when sitting
3. Sleep problems*
Pain constant
4. Sleep problems*
Pain worse when bending
5. Sleep problems*
Pain worse when walking
6. Sleep problems*
Pain worse when walking
Pain constant
7. Sleep problems*
Pain worse when walking
Pain constant
Pain worse when bending
* Sleep problems consist oi: pain wakes trom sleep, need sleep medications, or unable to sleep.
TABLE 6. Sensitivity and specificity of symptoms combined in parallel.
JOSPT Volume 21 Number 1 January 1995
are very painful or very expensive,
and the disease is not life-threatening
or there is little benefit from early
detection, then high specificity may
be important. On the other hand, if
failure to identify a patient at j e o p
ardy prolongs suffering and risks
death or disability, then high sensitivity may be critical. Although it may
be argued that the diagnostic
work-up for a serious low back problem is expensive, a stronger case can
be made for the importance of identifying and referring patients who
have low back problems that cannot
be managed by physical therapy
alone.
The combination of symptoms
that includes the three sleep distur-
RESEARCH
STUDY
Sensitivity: 1 l5/l33 = .86.
Specificity: 2 1/41 = .5 1.
Symptoms considered in parallel: I ) walking aggravates pain, 2) pain wakes from sleep, 3) need sleep medications,
and 4) unable to sleep.
TABLE 7. Sensitivity and specificity when screening in parallel.
bance symptoms and pain worsened
by walking has a sensitivity of .87.
This means that 87% of individuals
with serious low back problems would
report at least one of these symp
toms. This same combination of
symptoms had a specificity of .50.
This indicates that 50% of the patients with a benign low back p r o b
lem would report none of these
symptoms. Unfortunately, it is also
true that 50% of patients with benign
low back problems would report at
least one of these symptoms.
A clinician involved in screening low
back pain patients might also want to
know what proportion of the patients
who screen positive actually have a serious low back problem. The proportion
of patients who actually have the prob
lem, out of all those who have tested
positive, is known as the positive predictive value of a screening test (4,6). The
positive predictive value depends on
both the sensitivity of the test and the
prevalence of serious low back problems
in the population of low back pain pz+
tients being screened. Because this study
oversampled serious low back problems,
the prevalence of serious low back prob
lems in this .sample did not reflect the
prevalence of serious low back pain in a
typical clinic population. Therefore, the
positive predictive power of the symp
toms and combination of symptoms
could not be accurately estimated. Addii
tional prospective studies in a variety of
settingx will be required to clarifjr this
point
This was a retrospective study
and was, therefore, limited to the
information available in the standardized intake questionnaire. For that
reason, this study only dealt with patient symptoms. Although it was possible to correctly classify a large proportion of patients as having either
benign or serious low back problems
using only self-reported symptoms, it
is possible that the additional information from a physical examination
would have improved the classification of patients as either serious or
benign. Screening based on symp
toms should be viewed as a first step
in identifying patients with serious
low back problems. Additional studies
will be required to determine which
aspects of the physical examination,
in combination with the patient's
self-reported symptoms, will produce
the highest levels of sensitivity and
specificity in identifying patients who
require assistance outside the realm
of physical therapy.
CONCLUSION
The results of this study demonstrate a number of important findings. First, there are a number of
symptoms that are highly specific for
serious low back problems, since very
few patients with benign back p r o b
lems report these symptoms. Unfortunately, these same symptoms have
low sensitivity, indicating a large
number of patients with serious back
problems do not report these symp
toms either. Second, by considering a
number of symptoms together, it is
possible to increase sensitivity to the
point that very few patients with serious back problems are not identified.
However, the cost for this increased
sensitivity is an increase in the number of patients with benign low back
problems who also screen positive.
Therefore, the decision to refer such
a patient for additional diagnostic
work must be based on the entire
history of the patient's illness, including previous diagnostic work, the
physical examination, and the results
of the screening test.
lOSlT
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Volume 21 Number 1 January 199.5 JOSPT