From what I've read on the ClotCare site, some DRs use the d dimer while the patient is still on warfarin to determine whether to come off warfarin so if it were that unreliable when someone is on warfarin, don't think they'd do that. My doc feels they are reliable while on warfarin.

Warfarin doesn't dissolve clots. It prevents clots from forming which is why the chances of clotting while in warfarin are way low.

First, warfarin doesn't dissolve clots, it only keeps them from getting bigger. Your body has to dissolve the clots, but it can't really do that if they're still growing. So, the warfarin stops the clot from growing (and new ones from forming) and your body does the work of dissolving the clot and healing any damage that it caused.

Also, d-dimers are somewhat controversial tests because they can be affected by many things. It's easy to get false positive but hard to get false negatives. A false negative is probably a pretty good sign that you're not clotting (something that it would be hard to do on warfarin anyway). A false positive might be a clot, but it can also be affected by being sick and some other things.

My doc always refused to run d-dimers on me because I have chronic clotting in my right leg and she figured the test might be inaccurate.

I'm not entirely clear on how d-dimers work (maybe someone else can chime in) so I don't know if they'd be affected by having warfarin in your system or not. However, if you're on warfarin, the chances of clotting are really miniscule.

Haha I shouldn't have used the word dissolve in reference to warfarin. I know it doesn't do that...my bad.

D-dimer is a test for a substance that is released into the bloodstream during the active formation of clots. It can also be present in the bloodstream from other sources than clots (hence the MDs using clinical indications and other tests to confirm DVT/PE in case of a positive D-dimer test). If it's negative, your body is not forming new clots. Period. The test is mostly used to justify further, more invasive testing for clots in the body -or- to rule out a clot so the MD can focus on what else might be causing your symptoms (cellulitis, asthma, etc.) It can never be used by itself to confirm the presence of thromboembolic disease, but it can be used to rule it out.