I have heard from several residents that d-dimer is not accurate in patients who have been in the hospital for longer than a few days, but not sure why.
Is this true? Do you know why?
also a clot present for > 1 week may have a neg d-dimer.
it is a marker of acute clot formation.
I have seeen several fairly large pe's and dvt's with neg d-dimer assays in folks with sx over 1 week.
apparently there are several assays out there and the elisa is a better assay than the non-elisa.
I find wells crieteria fairly worthless, too ambigous. anyone you are considering seriously has at least a mod prob due to the last criteria( + 3 if PE is more likely than another dx).
I like the perc criteria better as it uses solid #s.
the problem with both is a pregnant female smoker with a pulse of 105 and a cough with pleuritic chest pain who has asthma and this may or may not be different than a typical exacxerbation.....
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
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.
I once has an ICU private attending tell me to order a DDimer on a patient with active cancer, on chemo, with a hx of PE who was tachypnic, tachycardic and hypoxic "because Ddimer has a great NPV.".
Once the pvt attending left, I ordered a CT angio and used this as a teaching example of how a negative predictive value in a HIGH prevalance patient population is meaningless.
I have a pt with low clinical prob (well's of 0, unlikely) but presents with CP and SOB. A CXR demonstrated an inflitrate c/w PNA. I thought that this was an ok setting in which to order a D-dimer since the pt did have SOB and CP and PE should be considered part of the differential although unlikely. The pt does not have a h/o malignancy or recent surgery, however she is elderly. I ordered the D-dimer and it was positive. What obligation do I have to continue with further testing imaging? I had ordered the D-dimer on admission and by the following day the pt had improved on IV abx. Her dx almost certainly PNA. I ordered the D-dimer b/c if it was neg it would have been very useful but a positive result is near useless due to notorious lack of specificity of the test. As a medical student in Montreal I observed that there was little obligation to cont with further testing. As a resident in the US however I've found that people really try to avoid ordering D-dimers in low prob pts (which is when you are supposed to order them) b/c then if it is positive there is an obligation to cont to test even if the pt is improving. My thought is that if the pt improves w/ Rx for the more likely dx a positive D-dimer in doesn't mean much but if they don't then it is something to keep in the back of one's differential... what are people's thought on this? I want to keep ordering D-dimer's in my low prob pts but I don't want to feel like I have to follow every positive up with a scan.