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Use of a Clinical Decision Rule in Combination With D-Dimer Concentration in Diagnostic Workup of Patients With Suspected Pulmonary Embolism
A Prospective Management Study
Marieke J. H. A. Kruip, MD;
Marjan J. Slob, MD;
Joost H. E. M. Schijen, MD;
Cees van der Heul, MD;
Harry R. Büller, MD
Arch Intern Med. 2002;162:1631-1635.
ABSTRACT
| |
Background We designed a diagnostic strategy, based on clinical probability and
D-dimer concentration, to select patients who were unlikely to have pulmonary
embolism (PE), before further diagnostic workup was performed. The utility
and safety of this strategy were evaluated in a prospective management study.
Methods Consecutive patients with suspected PE had D-dimer testing and clinical
probability assessment with a clinical decision rule. Patients with a low
probability and a normal D-dimer concentration (<500 ng/mL) were considered
not to have PE, and further diagnostic testing and anticoagulant therapy were
withheld. In patients with a low probability and elevated D-dimer level or
with a moderate or high probability, bilateral compression ultrasonography
of the legs was performed. If deep venous thrombosis was detected, venous
thromboembolism was diagnosed. If compression ultrasonography was normal,
pulmonary angiography was performed. All patients were followed up for 3 months.
Results Of the 234 consecutive patients, 26% had the combination of a low probability
and normal D-dimer level. During the follow-up period, none of these patients
died and 3 patients had recurrent complaints of PE. In these 3 patients, PE
was excluded by objective testing. The 3-month thromboembolic risk was therefore
0% (95% confidence interval, 0%-6%). The prevalence of PE in the entire population
was 22%.
Conclusions The combination of a low clinical probability and a normal D-dimer concentration
appears to be a safe method to exclude PE, with a high clinical utility, and
is readily accepted by clinicians.
INTRODUCTION
DIAGNOSING OR excluding pulmonary embolism (PE) is difficult because
the clinical manifestations are nonspecific.1
Less than 30% of patients presenting with signs and symptoms suggestive of
PE actually have the disease confirmed by objective testing.2-4
As a result, the diagnostic approach has gradually changed from trying to
confirm PE to also identifying the large proportion of patients who do not
have the disease. Several methods have recently been advocated for excluding
PE.
Clinical assessment has been used to stratify patients with suspected
PE into low, moderate, and high clinical probability categories. Studies have
been performed with the use of clinical judgment, as well as a structured
algorithm, to achieve this stratification. However, in 3% to 28% of patients
with a low clinical probability, PE was subsequently confirmed to be present.2, 5-10
These figures are too high to safely exclude PE in symptomatic patients on
the basis of the clinical probability assessment alone.
The finding of a normal plasma concentration of D dimer, the degradation
product of cross-linked fibrin, was shown to be able to exclude PE accurately
in most patients presenting with clinical suspicion. The sensitivity and negative
predictive value vary depending on the type of D-dimer assay, but with the
current rapid tests, both are usually high (90%-100% and 94%-100%, respectively).6, 11-17
To safely exclude PE, the sensitivity should approach 100%. This is important
because, for every 2% decrease in sensitivity, 1 per 1000 patients studied
will die of recurrent PE as a result of inappropriately withholding anticoagulant
therapy.18 Most D-dimer assays do not have
a sufficiently high sensitivity to be safely used and accepted by clinicians
as the only method to exclude PE.
Hence, the combination of clinical assessment and D-dimer concentration
may be well suited to differentiate between patients who will probably have
PE and those who will not have this disease. Findings in recent studies in
patients with suspected venous thromboembolism (VTE) support this assumption.6-7,19 The aim of the present
study was to evaluate the utility and safety of a novel strategy in excluding
PE in patients with a low clinical probability, according to a validated clinical
decision rule,7 and a normal D-dimer concentration.
In these patients, no further diagnostic investigations were performed and
anticoagulant therapy was withheld. In the remaining patients we used compression
ultrasonography (CUS), followed by pulmonary angiography if results were normal.
PATIENTS AND METHODS
PATIENTS
Consecutive inpatients and outpatients older than 16 years, with clinically
suspected acute PE seen at St Elisabeth Hospital, Tilburg, the Netherlands,
were prospectively included in the study between January 1, 1998, and May
31, 2000. The protocol was approved by the local ethics committees, and written
informed consent was obtained from all patients.
STUDY DESIGN AND DIAGNOSTIC STUDIES
The clinical decision rule (CDR) was completed and the patients were
stratified into low, moderate, and high clinical probability categories of
PE. The CDR consists, as described elsewhere,7
of risk factors for PE, signs and symptoms from history and physical examination,
chest radiography, oxygen saturation tests, and electrocardiography, as well
as the likelihood of an alternative diagnosis for the patient's symptoms.
The CDR was applied by a group of at least 10 attending physicians, who all
received extensive instructions about how to use the rule before the start
of the study. The plasma D-dimer concentration was then measured with a quantitative
rapid enzyme-linked immunosorbent D-dimer assay (Vidas DD; bioMérieux,
Inc, Paris, France). The concentration was expressed in nanograms per milliliter
of fibrinogen equivalent units. The cutoff value, according to the manufacturer's
instructions, was 500 ng/mL. All measurements were carried out in duplicate
by a technician who was unaware of the outcome of the CDR and the patient's
history.
Patients with a low probability of PE and a normal D-dimer test result
(<500 ng/mL) did not undergo further diagnostic procedures and anticoagulant
treatment was withheld. They were instructed to return to the thrombosis unit
immediately when signs or symptoms of PE or deep venous thrombosis (DVT) recurred,
and appropriate objective testing (CUS, lung scanning, or pulmonary angiography)
was performed to confirm or refute the diagnosis.
In patients with a low probability of PE and elevated D-dimer concentration,
or moderate or high clinical probability, first bilateral CUS of the legs
was performed within 24 hours. The femoral vein was visualized in the supine
position in its full length and the popliteal vein was investigated in the
prone position to the trifurcation. Visualization of a clot, ie, not being
able to compress the vein and lack of flow, was considered to be abnormal
and to indicate the presence of DVT.
When a DVT was present, VTE was diagnosed and treatment with anticoagulants
was initiated. If CUS was normal, selective pulmonary digital substraction
angiography was performed within 48 hours after initial presentation. A 7F
Swan-Ganz flow-directed pulmonary angiography true-size catheter was positioned
into a main pulmonary artery and selectively in the lobar arteries of both
lungs. Subselective magnification series were obtained of lower, middle, and
upper portions of both lungs with the catheter in lobar and segmental branches.
Anteroposterior projections were obtained routinely; different projections
and/or selective series were obtained if the initial images were not conclusive.
Bilateral pulmonary angiography was performed in all patients. The following
criteria were considered diagnostic of PE: a constant intraluminal filling
defect or a persistent acute cutoff sign of an arterial pulmonary branch seen
on more than 1 projection. In case of doubt, a second experienced radiologist
was asked for his opinion and the diagnosis was made by means of consensus;
if necessary, additional superselective series were performed.
THREE-MONTH FOLLOW-UP
All patients were reexamined by the study coordinator (M.J.H.A.K.) 1
week and 1 and 3 months after inclusion at the outpatient clinic or interviewed
by telephone. Suspected venous thrombotic events (PE or DVT) were investigated
by appropriate objective diagnostic methods within 48 hours of presentation.
When a patient was readmitted to the hospital for any cause, the charts were
reviewed. Venous thromboembolic events, as well as causes of death, were recorded
and adjudicated independently.
RESULTS
During the investigation period, 251 consecutive patients with clinically
suspected PE were studied. Seventeen patients (7%) were excluded because of
refusal or inability to give consent (5 patients), contraindications to pulmonary
angiography (2 patients), and absence of D-dimer measurement because of logistical
problems (10 patients).
Thus, the study population available for analysis consisted of 234 patients.
The mean age of this cohort was 51 years (SD, 17 years) and the prevalence
of VTE was 22%. Of the total population, 83% presented as outpatients and
11% had a history of previous VTE (Table
1). The 3-month follow-up period was completed in all patients.
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Clinical Characteristics of the 234 Study Patients With Clinically
Suspected Pulmonary Embolism*
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LOW CLINICAL PROBABILITY AND NORMAL D-DIMER CONCENTRATION
Figure 1 summarizes the results
of the evaluated diagnostic strategy. The clinical probability of PE, according
to the CDR, was low in 120 patients (51%), moderate in 74 patients (32%),
and high in 40 patients (17%). Of the patients with a low clinical probability,
60 had a normal D-dimer concentration, so no further diagnostic procedures
were performed and the patients did not receive anticoagulant therapy. This
subgroup represents 26% of the original study cohort. Fifty-six of these presented
as outpatients. Thus, in 4 (10%) of the 40 already hospitalized patients and
in 56 (29%) of the 194 outpatients, PE was excluded by this diagnostic strategy.
During the 3-month follow-up period, none of the patients with a low clinical
probability and a normal D-dimer concentration died, and 3 returned with new
complaints of PE (3, 14, and 16 days after initial presentation). In all 3
patients, PE was excluded (by normal pulmonary angiogram in 2 and normal perfusion
scan result in 1). Hence, the subsequent rate of VTE in this patient group
during follow-up was 0% (95% confidence interval [CI], 0%-6%).
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Results of the diagnostic strategy in 251 consecutive patients presenting
with clinically suspected pulmonary embolism (PE). CUS indicates compression
ultrasonography.
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PATIENTS WITH OTHER TEST OUTCOMES
Of the 174 patients with either a low clinical probability of PE but
elevated D-dimer concentration or a moderate or high clinical probability,
27 had a DVT as detected by bilateral CUS. This subgroup with confirmed VTE
by CUS represents 12% of the original study cohort. In the patients with a
normal CUS (n = 147), pulmonary angiography was performed. Pulmonary embolism
was present in 25 patients. Thus, a total of 52 patients had documented VTE;
hence, the overall prevalence was 22%. Of the 122 patients with normal pulmonary
angiograms, 1 presented with suspected PE 10 days after the initial pulmonary
angiogram. Pulmonary angiography was again performed and showed PE. Hence,
the subsequent rate of VTE in patients with normal pulmonary angiograms was
0.8% (95% CI, 0.02%-4.50%). During the 3-month follow-up period of these 122
patients, a total of 4 patients died. The causes of death were cancer in 3
and progressive chronic obstructive pulmonary disease in 1.
ADDITIONAL OBSERVATIONS
In the present study, only patients with a low clinical probability
of PE in combination with a normal D-dimer concentration were considered not
to have PE. If we had added the patients with a moderate clinical probability
and a normal D-dimer concentration to this group, a total of 85 (36%) of the
presenting cohort would have been spared further diagnostic procedures and
anticoagulant therapy. One of these 85 patients had PE involving the segmental
arteries, confirmed by pulmonary angiography (failure rate, 1.2%; 95% CI,
0.03%-6.40%). This patient was a 40-year-old woman who had recently had a
neurosurgical operation (9 days before presentation) and who presented with
a complaint of dyspnea of 3 days' duration. The remaining 149 patients, ie,
those with a low or moderate clinical probability and an elevated D-dimer
concentration or with a high clinical probability, would have undergone further
diagnostic procedures, which would have revealed PE in approximately one third
(51 patients).
The D-dimer concentration was measured in all patients. The result was
normal in 100 patients (43%) of the study population. One of these 100 patients
actually had PE in segmental arteries on pulmonary angiography (same patient
as described above). The D-dimer concentration of this patient was 480 ng/mL.
The sensitivity of the D-dimer assay was 98% (95% CI, 90%-100%) and the negative
predictive value, 99% (95% CI, 95%-100%).
COMMENT
The primary finding of this study is that the combination of a low clinical
probability of PE and a normal D-dimer concentration is able to exclude the
disease safely in a substantial proportion (26%) of patients presenting with
suspected PE. This new strategy was introduced in a large teaching hospital
that previously used lung scanning and pulmonary angiography and was well
accepted by the clinicians (physicians, internists, pulmonologists, and surgeons)
involved in the diagnostic workup of such patients.
Furthermore, the present study confirms that the combination of CUS
and pulmonary angiography is a feasible, effective, and safe subsequent diagnostic
strategy. Performing CUS of the deep leg veins in patients with a moderate
or high clinical probability or a low clinical probability and elevated D-dimers
levels (n = 174) was worthwhile: 16% had DVT detected by ultrasonography,
and anticoagulant treatment was initiated. Taken together, the use of the
clinical probability assessment, D-dimer assay, and CUS, all noninvasive methods,
was able to confirm or refute the diagnosis in 37% of the patients of the
original study cohort. Pulmonary angiography was performed without any complication,
confirming earlier observations,20 although
in 1 patient the initial PE was most likely missed. The outcome with respect
to subsequent episodes of symptomatic VTE during the 3-month follow-up in
patients with a low clinical probability and a normal D-dimer concentration
(failure rate, 0%; 95% CI, 0%-6%) compared favorably with that of patients
with normal pulmonary angiograms (failure rate, 0.8%; 95% CI, 0.02%-4.50%)
and is in agreement with studies using normal perfusion scan results or serial
ultrasound scan results to exclude VTE.4, 6-7,19, 21
Only a limited number of prospective management studies with D-dimer,
CDR, or a combination of both are available.6-7,19, 21
Our observations of the combination of CDR and D-dimer are comparable with
the findings of these studies. However, de Groot et al19
and Perrier et al6 used the combination only
in patients with a nondiagnostic perfusion-ventilation lung scan result, whereas
in the present study the combination was used as the first step in the diagnostic
workup. Therefore, a larger proportion of our study cohort, approximately
one quarter, was spared radiologic or nuclear investigations compared with
these studies.
In a recent study by Perrier and colleagues,21
D-dimer measurements were used as the first test in the diagnostic workup
of 444 outpatients with suspected PE. A total of 159 patients (36%) had normal
D-dimer concentrations, and this method was used as the sole test to exclude
VTE (subsequent failure rate was 0%; 95% CI, 0%-2.3%). If we had adopted a
similar strategy, while we used exactly the same D-dimer assay, we would have
missed 1 patient with significant PE, although our findings are still consistent
with the CIs of that study. It should be noted that we studied both inpatients
and outpatients and that combining clinical assessment and D-dimer testing
was readily accepted by the specialists who see patients with suspected PE.
Several studies using CUS and pulmonary angiography in patients with
suspected PE have been published. An abnormal venous ultrasonogram is found
in 5% to 12% of patients with a nondiagnostic lung scan result.6-7,22-25
In a meta-analysis by van Rossum et al,25 the
prevalence of DVT in patients with clinically suspected PE was approximately
18%, and in patients with proven PE, 36% to 45% (range, 10%-93%). Our observations
with respect to the proportion of patients with abnormal CUS are comparable
with the findings in patients with a high-probability lung scan result but
are higher than the proportion of patients with a nondiagnostic lung scan
result.6-7,22-25
Investigations that assessed the validity and safety of pulmonary angiography
found that this method may be falsely negative in approximately 1% and that
the morbidity and mortality rates associated with the test itself are very
low (0.4% [95% CI, 0.09%-1.25%] and 0% [95% CI, 0%-0.53%], respectively),
as was seen in the present study.2, 20, 26
Some aspects of our study warrant comment. Although we studied a consecutive
series of patients with suspected PE seen in a large teaching hospital, the
total number of patients included is moderate. In particular, in the subgroup
of patients with a low clinical probability of PE and a normal D-dimer concentration,
there remains some uncertainty about the safety of withholding further diagnostic
testing and anticoagulant treatment, since the upper limit of the 95% CI of
the 3-month thromboembolic risk was 6%. Similar outcome studies using other
strategies to exclude VTE usually had an upper limit of 4%.6, 21, 27-29
However, there is a wealth of evidence that D-dimer assays based on enzyme-linked
immunosorbent assays are effective in excluding significant VTE. Therefore,
it seems reasonable to conclude that a normal D-dimer concentration combined
with a low clinical probability of PE is safe. Further studies are required
to include patients with a moderate clinical probability.
We did not include perfusion-ventilation lung scanning in the present
strategy. This is mainly because of the limited availability of, in particular,
ventilation scanning and the often nondiagnostic test results. The strategy
used in this study eliminates the need for nuclear medicine facilities, which
may be relevant for those institutions without such services.
We conclude that the combination of a low clinical probability of PE,
assessed by a CDR, and a normal D-dimer concentration contributes to the increasing
body of evidence that this is a rapid and cost-effective method to exclude
PE safely, and that this strategy is readily accepted. The combination of
CUS and pulmonary angiography remains a valid and effective approach for patients
with suspected PE.
AUTHOR INFORMATION
Accepted for publication November 29, 2001.
We thank all physicians of the Internal Medicine, Pulmonology, and Radiology
departments for participating in the study and treating the patients by the
diagnostic strategy. We thank J. de Jongh-Leuvenink, PhD, and the technicians
of the clinical chemical laboratory for performing the D-dimer assay.
Corresponding author and reprints: Marieke J. H. A. Kruip, MD, Department
of Internal Medicine, St Elisabeth Hospital, Postbus 90151, 5000 LC, Tilburg,
the Netherlands (e-mail: evert.janssen{at}zonnet.nl).
From the Departments of Internal Medicine (Drs Kruip and van der Heul),
Radiology (Dr Slob), and Pulmonology (Dr Schijen), St Elisabeth Hospital,
Tilburg, and Department of Vascular Medicine, Academical Medical Centre, Amsterdam
(Dr Büller), the Netherlands.
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A Combined Approach to Ruling Out Pulmonary Embolism
JWatch General 2002;2002:1-1.
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