We live in strange, complicated times. Popular to our twisted reality are haphazard panels of cardiac biomarkers, ordered unthinkingly via triage protocol or unwittingly by physicians using order sets. Troponins, myoglobin, creatinine kinase, brain naturetic peptide, and, sometimes, D-dimer results will arrive on patients for whom no suspicion of cardiovascular disease is present.
So, what do you do with that positive D-dimer in a patient who, until just that moment, appeared to be zero-risk for pulmonary embolism – possibly, say, by PERC?
This retrospective chart review from four French hospitals identified all patients undergoing D-dimer testing as part of evaluation for pulmonary embolism. Of 2,791 patients screened with complete data, 1,070 were PERC negative. Of these 1,070 minimal risk patients, 167 had positive D-dimer. 153 of these 167 underwent diagnostic imaging for PE, with 5 detected. Therefore, in this cohort, a patient who was PERC negative with a positive D-dimer had approximately 3.0% incidence of PE.
This result is, however, absent any other abstracted objective risk-stratification. PERC was designed to work in concert with other objective or gestalt risk-stratification into a low-risk cohort. So, even though these authors claim a number of unnecessary imaging studies, it is likely a handful of these were reasonable tests utilizing risk factors outside of PERC.
Regardless, please carry on properly ignoring the majority of inadvertent positive D-dimers – if PE is not reasonably in the differential, as it was in this study, the prevalence of PE will still be vanishingly small.
“Pulmonary Embolism Rule-out Criteria vs D-dimer testing in low-risk patients for the diagnosis of pulmonary embolism: a retrospective study in Paris, France.”
http://www.ncbi.nlm.nih.gov/pubmed/24736129
The "Dammit" D-dimer is also commonly found hiding in the chart of the patient who was *just* signed out to you. No CP, no SOB, and no mention from the other team, but there it sits on the screen in red.
given almost all the patients who were imaged, had CTPA as their imaging modality which has a false positive rate of about 50% in low risk cohorts with prevalence rates around 3%, it is likely that the true positive prevalence rate of PE in this population of PERC negative, d-dimer positive patients is probably even less eg 1-2%. Adding to this the likelihood that they are also simultaneously have low prognostic risk given they are negative to PERC criteria, it is almost certain that this group are below the test threshold. Even more impressive is that this all occurred in a high prevalence population in Europe where the patient groups being investigated for PE in ED's generally have pre test probabilities of 20-30%.
" Of these 1,070 minimal risk patients, 167 had positive D-dimer. 153 of these 167 underwent diagnostic imaging for PE, with 5 detected. Therefore, in this cohort, a patient who was PERC negative with a positive D-dimer had approximately 3.0% incidence of PE."
Hello there!
This can also be translated into :
" Therefore, in this cohort, a patient who was PERC negative had approximately a 0.5% incidence of PE"
But retrospectively implemented PERC may differ from prospective daily usage.
Agree with both Anand and axel – the retrospective nature and the lack of other clinical characteristics of patients limits the conclusions that can be made. Were some of these PERC-negative patients otherwise moderate-risk for PE? Entirely possible. Is the specificity of CTPA acceptable in a ~3% prevalence population? No. Excellent points.
Hi
CTPA specificity depends on the actual result. That is a case by case issue. When there is a big size thrombus in a proximal PA, then there is no doubt there is a PE.
I remember a > 10 years old case I had that illustrates what was said above in comments and post. Frustrating case.
I'm handed over a young patient with a clear cut common cold and an acute chest pain of sudden onset : localised pain, pinpointedly elicited with gentle pressure with one finger on one rib.
Patient otherwise well, is professionally active , with a strange vasculitis treated with clopidogrel and I don't remember whether she was on steroids or immunosuppressant.
I look at the bloods and I don't see a d-dimer had been ordered.
I discharge her on pain meds.
I get a call from my hospital 2 days later asking permission to release the D Dimer result to the emergency doc at St Elsewhere Hospital. I say OK and realise D Dimer was mildly elevated. Out of memory 0.7 µg/mL.
On that basis the St Elsewhere ED doc orders a CTPA that shows one (1) tiny subsegmental thrombus. No idea whether consistent in location with the pain or not . Patient admitted to an unrelated specialty ward (no appropriate bed available as usual). I call the local fellow who tells me he doesn't think she has PE but the CT was shown to pneumopod who says the image is a thrombus. So she was treated for a non-PE. ANd I know she survived the anticoagulants (plus clopidogrel). And she has now a wrong PMH of PE. ANd likely curses me on a reguar basis for missing her PE.
Cuz'of a D Dimer that should'nt have been ordered in the first place….
HArumph !
I'll keep anonymous for this case. Sorry
it is true as "Anon" says that CTPA specificity depends on the PE location. On average the false positive rate in a 3% prevalence population is about 50% but if main or lobar PE it is likely to be a true positive while if segmental or subsegmental it is more likely to be false