Welcome to Yesterday, Have You Heard of PERC?

I usually like these sorts of articles regarding the yield and utilization of CT pulmonary angiograms.  They’re fun to dissect, useful to marvel at the inefficiency of our usage, and finally to feed my editorial hyperbole.  But, not this time.

This is a retrospective study from the University of Michigan comprising six months of CTPA data from 2013.  These authors reviewed charts on 602 consecutive patients and calculated modified Wells and PERC for each, and describe the appropriateness and yields of various cohorts.

Rather than detail these statistics and outcomes – other than to note their overall yield of 61 positives reported out of 602 scans – I’d rather just focus on the 108 patients scanned who were PERC negative.  PERC has been around since 2004, and it’s been percolating into various guidelines and evidence-based algorithms since.  Hello, it’s 2015: why are almost 20% of CTs at an academic medical center PERC-negative?

The authors state two PERC-negative patients had positive CT findings; given the pretest probability, I wouldn’t be surprised if one or both were ultimately false-positives.  Come on, man.

“CT Pulmonary Angiography: Using Decision Rules in the Emergency Department”
http://www.ncbi.nlm.nih.gov/pubmed/26435116

6 thoughts on “Welcome to Yesterday, Have You Heard of PERC?”

  2. The problem I have with PERC is that you need a gestalt clinical probability < 15% to use it.

    Well, you said 15 % ?
    It just could be 16%, 14% or 16.7% , I just can't fathom that.

    Now Wells < 6 is less than 16% PE incidence, and Geneva modified less than 10.n%.

    This is not 15% and PErC was not assessed with scores.

    Maybe I should just use it when hesitating ordering a D dimer dosage.

  4. 2/100 pos., yes that's appropriate to PERC miss rate, who knows if false pos?

    To Dr. Ellrodt, the "can't use PERC" grp presumably lives in the 80% "not PERC neg." portion. And it's possible, to your point, that some of the 108 were mod to high risk based on clinical presentation. But we know none were tachy or hypoxic. We can argue specifics but we should be able T agree that we scan too many people, and arguably the wrong people, looking for this dz.

  5. 2/100 pos., yes that's appropriate to PERC miss rate, who knows if false pos?

    To Dr. Ellrodt, the "can't use PERC" grp presumably lives in the 80% "not PERC neg." portion. And it's possible, to your point, that some of the 108 were mod to high risk based on clinical presentation. But we know none were tachy or hypoxic. We can argue specifics but we should be able T agree that we scan too many people, and arguably the wrong people, looking for this dz.

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