Diagnosis
 Accuracy of Clinical Assessment in the Diagnosis of Pulmonary Embolism
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Summary
Posted By: Anthony Delaney
E-Mail: apdelane@doh.health.nsw.gov.au
Posted Date: 11/4/02
Title: Accuracy of Clinical Assessment in the Diagnosis of Pulmonary Embolism
Authors: MASSIMO MINIATI, RENATO PREDILETTO, BRUNO FORMICHI, CARLO MARINI, GIORGIO DI RICCO, LUCIA TONELLI, GERMANA ALLESCIA, and MASSIMO PISTOLESI
Reference: Am. J. Respir. Crit. Care Med., Volume 159, Number 3, March 1999, 864-871
Link: Click here for a direct link to the paper. A password may be required for access to fulltext.
Abstract: To provide clinical diagnostic criteria for pulmonary embolism (PE), we evaluated 750 consecutive patients with suspected PE who were enrolled in the Prospective Investigative Study of Acute Pulmonary Embolism Diagnosis (PISA-PED). Prior to perfusion lung scanning, patients were examined independently by six pulmonologists according to a standardized diagnostic protocol. Study design required pulmonary angiography in all patients with abnormal scans. Patients are reported as two distinct groups: a first group of 500, whose data were analyzed to derive a clinical diagnostic algorithm for PE, and a second group of 250 in whom the diagnostic algorithm was validated. PE was diagnosed by angiography in 202 (40%) of the 500 patients in the first group. A diagnostic algorithm was developed that includes the identification of three symptoms (sudden onset dyspnea, chest pain, and fainting) and their association with one or more of the following abnormalities: electrocardiographic signs of right ventricular overload, radiographic signs of oligemia, amputation of hilar artery, and pulmonary consolidations compatible with infarction. The above three symptoms (singly or in some combination) were associated with at least one of the above electrocardiographic and radiographic abnormalities in 164 (81%) of 202 patients with confirmed PE and in only 22 (7%) of 298 patients without PE. The rate of correct clinical classification was 88% (440/500). In the validation group of 250 patients the prevalence of PE was 42% (104/250). In this group, the sensitivity and specificity of the clinical diagnostic algorithm for PE were 84% (95% CI: 77 to 91%) and 95% (95% CI: 91 to 99%), respectively. The rate of correct clinical classification was 90% (225/250). Combining clinical estimates of PE, derived from the diagnostic algorithm, with independent interpretation of perfusion lung scans helps restrict the need for angiography to a minority of patients with suspected PE.
 
Are the Results Valid?
1. Was there an independent, blind comparison with a reference standard?
The reference standard used to confirm the clinical parameters was a perfusion lung scan and if the perfusion lung scan was abnormal, pulmonary angiography was used to confirm or exclude the diagnosis. The perfusion scan was read independently. This reference standard is probably reasonable, as patients with normal lung perfusion scans have a very small chance of having clinically significant pulmonary embolism. It does however leave the potential for a degree of inaccuracy, ie some of the patients with normal perfusion scans could have had pulmonary embolism on angiography.
2. Did the patient sample include an appropriate spectrum of patients to whom the diagnostic test will be applied in clinical practice?
Probably. 85% of the patients were inpatients when enrolled in the study, so it may not be as accurate in an outpatient or Emergency Department setting. The spectrum of severity ranges from 1-14 unperfused segments (maximum of 18), however the numbers in each range of severity are not described.
3. Did the results of the test being evaluated influence the decision to perform the reference standard?
No. All patients had a perfusion lung scan regardless of the clinical findings however the decision to do pulmonary angiography was based on the perfusion scan results.
4. Were the methods for performing the test described in sufficient detail to permit replication?
Yes, the methods used to define the clinical parameters were reasonably well defined in the methods section.
What are the Results?
1. Are likelihood ratios for the test results presented or data necessary for their calculation provided?
For the symptoms (at least one of sudden onset dyspnoea, pleuritic or substernal chest pain, fainting:
sensitivity 96%,
specificty 59%,
likliehood ratio for a postive test 2.2,
likliehood ratio for a negative test 0.07,
positive predictive value 53%,
negative predictive value 94%,

When the clinical symptoms were associated with at least one of the ECG or CXR abnormalities the results were;
Sensitivity 81%,
specificity 93%,
Likliehood ratio for a positive test 11.6,
likliehood ratio for a negative test 0.2,
positive predictive value 88%,
negative predictive value 88%.
Will the Results Help Me In Caring For My Patients?
1. Will the reproducibility of the test result and its interpretation be satisfactory in my setting?
The assesment of patients, ECG's and CXR's was performed by specialist respiratory physicians. They were directed to look for the specific abnormalities, so the results may not be so impressive when the clinical assessment is undertaken by people with less experience and guidance.
2. Are the results applicable to my patient?
There is nothing to suggest that this population of patients is particularily unique, so the results should be generalisable.
3. Will the results change my management?
Being able to define a clinical probability of pulmonary embolism is important as it will help to define which patients should have therpay started before confirmatory testing and how the confirmatory testing (V/Q scan, CT or pulmonary angiography) will be interpreted.
4. Will patients be better off as a result of the test?
Patients have the potential to be better off if the correct diagnosis can be reached, accurately, in the least invasive way posssible. This study suggests that this is possible

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