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Make the Diagnosis: Pulmonary Embolus

Prior Probability

Venous thrombosis occurs in 1 to 2 persons per 1000 person-years, with approximately one-half to one-third of these episodes from pulmonary embolism.18 In published studies, the prevalence of pulmonary embolism in patients who present with a clinical suspicion ranges from 9% to more than 30%,19 which undoubtedly relates to a combination of factors, including differences in referral patterns and health practices among countries, as well as differences in patient populations. The prior probability of a pulmonary embolus is determined from the clinical findings. Although studies vary in the prevalence of disease, a useful guideline would be to think of “low probability” as approximately less than 15% and “moderate probability” as 15% to 35%.

Population for Whom Pulmonary Embolus Should Be Considered

Patients who have had recent major surgery, major trauma, immobility, or active malignancy are some of the highest-risk groups within the general population, with relative risks varying from 5 to 200.20 The most common presenting symptoms of pulmonary embolism are new or worsening dyspnea, acute chest pain, and, less frequently, cough, fainting, or hemoptysis. Tachypnea and tachycardia, the most common signs of pulmonary embolism, occur frequently with exacerbations of chronic obstructive lung disease, congestive cardiac failure, and pneumonia, which highlights the poor specificity of these signs.21

Detecting the Likelihood of Pulmonary Embolus

Use a structured model to assess the pretest probability of pulmonary emboli. The simplified Wells scoring system may be the easiest to use in clinical practice, shows good reliability, and requires no laboratory tests or radiographs (see Table 43-12).

Table 43-12Simplified Wells Scoring System

Establishing the pretest probability before, and not after, reviewing the results of a sensitive D-dimer test will identify patients at very low risk for pulmonary emboli (see Table 43-13).

Table 43-13The Likelihood Ratios for Pulmonary Embolus for the Combination of Clinical Probability Estimate With the D-dimer Result

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