I had an uedvt 7 years ago. now i apparently have another but have neg d dimer. is it possible the u/s was read wrong and i don't have a clot?

DVT: It is possible the ultrasound is wrong, but it is also possible that you have a DVT and normal d-dimer as well. I would repeat the ultrasound. If they aren't 100% sure on the u/s, a venogram can be done but is probably not necessary. You need a hematologic work up to see why you are hypercoagulable.

DVT diagnosis: Ultrasound is extremely accurate at diagnosing a dvt, so it is very likely that there is another one, even with a negative d-dimer. The limitation of ultrasound is that it cannot tell if the clot is new / fresh or whether it is an old clot that has been there for some time. The d-dimer would only be positive if the the clot just recently formed and is fresh / new. Without a known age, treat it.