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Make the Diagnosis: Deep Vein Thrombosis

Prior Probability

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

Table 18-14Simplified Wells Prediction Rule2

Population for Whom Deep Vein Thrombosis Should Be Considered

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.

Detecting the Likelihood of Deep Vein Thrombosis

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).

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

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