I hear ya. I like the PERC, too... but it isn't validated in as robust a population as the Wells. Besides, PERC or Wells, anyone you are considering "seriously" isn't the patient to get a d-Dimer anyway... that patient should be getting a more definitive test. Your mythical patient above, for instance, would get a V/Q in my ER, I wouldn't even order the damn d-dimer. Plus, someone who is pregnant is gonna have a positive d-Dimer no matter WHAT the symptoms are. The Wells criteria -- and the PERC = FFP (far from perfect). But even though they're imperfect tools, they've saved many a CT scan in my practice when my gestalt KNOWS they don't have a PE, but I need something more to reference (than my gestalt) in the decision-making context of my documentation.
It's all a game, my friends