Here is a post from Ryan Radecki at EM Lit of Note. His philosophy mirrors what I took from Jeff Kline the PE guru on the approach to PE workup. When you have committed to ordering a CT-PA, then get a d dimer and if NEG, CANCEL the CT. Controversial of course. But the dimer is MORE SENSITIVE than a CT. Some say the d dimer is only for “low risk” patients, but check out this study using not necessarily low risk patients.