Evaluating the average Joe/Jane for pulmonary embolism is rather straightforward – but let’s not go back into that morass of practice variation and low-value over-diagnosis. This is an a study looking at how to diagnose PE during pregnancy, which is fraught with its own unique issues.
Firstly, obviously, CTPA ought to be avoided whenever possible – and moreso when there is a chance of fetal exposure. When the benefits outweigh the risks, of course, it is reasonable to proceed. Then, use of D-dimer as a tool to inform the posterior probability of PE is challenged by its steady increase in pregnancy. This combination of issues results in general uncertainty with regard to the approach.
This is their algorithm:
Over the course of eight years, at 11 centers, these authors included 395 patients in their study – 357 of whom were evaluated per-protocol. Only a handful were assessed as “high” risk, while the bulk underwent D-dimer testing with a test threshold of 500 µg/L on the Vidas assay. The D-dimer was virtually useless, with only 46 of 392 being excluded from further evaluation. Then, the bilateral lower extremity ultrasound was basically useless, with only 7 positives out of 349 performed – resulting in 342 CTPAs. There were 19 positive CTPA, and then two of the inconclusive CTPA were ultimately diagnosed with PE by V/Q scanning.
What a mess. For those keeping score at home, that’s 7.1% yield for their evaluation of PE, and all their extra hoops prevented little radiation exposure. From a diagnostic evaluation standpoint, of course, their protocol was entirely adequate with regard to missed PE – unsurprising because most patients received all the tests in their algorithm.
The ugliest observation here is their prevalence of 7.1% is actually far lower than the prevalence observed in the non-pregnant population in Europe. Step one in fixing this approach: just apply the same gestalt to this population as the remainder of ED presentations. Then, let’s adopt the YEARS protocol, at a minimum, and consider adopting trimester-adjusted cut-offs for D-dimer. The miss rate will not be zero – but, incorporating appropriate clinical judgment, the net harms from untreated PE will be balanced by the benefit of avoided radiation, anticoagulation, and over-diagnosis.
“Diagnosis of Pulmonary Embolism During Pregnancy: A Multicenter Prospective Management Outcome Study”
http://annals.org/aim/article-abstract/2708166/diagnosis-pulmonary-embolism-during-pregnancy-multicenter-prospective-management-outcome-study