Bottom line: In a patient in which DVT/PE is in the differential, consider the d-dimer test, but use Well's criteria to stratify your patient into "zero", "low", "moderate", or "high" risk. If your patient is virtually zero or low risk, the d-dimer has utility NOW and should be ordered. If high risk, skip the d-dimer and go to imaging. If moderate, the d-dimer MAY have utility after the fact if the imaging study is inconclusive (such as in the case of an indeterminate VQ scan) but most would say that even in this case, the d-dimer is of inferior utility to, say, getting another study such as CT PE protocol or bilateral lower limb ultrasounds.