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Make the Diagnosis: Deep Vein Thrombosis

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Prior Probability

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A validated clinical prediction rule, applied to the appropriate patient population, creates stratified probability estimates of DVT (see Table 18-14).

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Table 18-14Simplified Wells Prediction Rule2
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Population for Whom Deep Vein Thrombosis Should Be Considered

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Deep vein thrombosis should be considered in patients with an acutely swollen leg that is causing discomfort, even though it can be bilateral and occur without prominent discomfort.

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Detecting the Likelihood of Deep Vein Thrombosis

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Because the prediction rule has been validated for the pretest probability and because the likelihood ratio (LR) varies according to the probability estimates and D-dimer assay, it is easier to display the posttest probability estimates without the LRs. Clinicians must know whether their laboratory uses the high-sensitivity D-dimer assay or the moderate-sensitivity assay. The clinical probability estimates must be determined before the D-dimer result is revealed to the clinician. Of all the findings, a negative high sensitivity D-dimer result has the biggest effect on the probability of disease and for many patients will provide evidence that obviates the need for imaging (see Table 18-15).

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Probability of Deep Vein Thrombosis After First Determining the Clinical Probability and Then Obtaining the D-dimer Result

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