Sunday, January 15, 2012

PERC - Still (Mostly) Useless

...except, perhaps, in a risk-management sense - but, only if we keep beating it down into its narrowest application due to its terrible specificity.

This most recent Annals publishes a systematic review of the Pulmonary Embolism Rule-Out Criteria, a decision instrument recommended in ACEP's pulmonary embolism clinical guidelines as a reasonable tool to risk-stratify a patient into a so-called "zero-risk" population that does not require any testing - not even a D-dimer.  And, I think they do a reasonable job including studies and summarizing the data, especially considering the width of the error bars on a lot of these studies.

The key points - pooled sensitivity is 97% when applied to a low-risk (Wells, Geneva, gestalt, whichever) population with a negative LR of 0.18.  This means, if you had someone who you already didn't think had a PE and they meet PERC criteria, it helps you with your medicolegal documentation, since it's in ACEP's guidelines.  The negative LR is strong enough to be helpful - but when you're already looking at single-digit percentage risk for PE, the absolute reduction in risk is quite small.

The important point to hammer home is the positive LR is only 1.23, which makes it the D-dimer of decision instruments.  Please don't justify further work-up just because they fail PERC - it barely moves the needle with its terrible specificity.  You need to have another clinical justification for further work-up in pulmonary embolism.

As an aside, in this era of over-testing and over-diagnosis of PE, the diagnosis of PE isn't necessarily the ideal endpoint - what we should be following are patient-oriented outcomes such as death/heart failure in untreated PE in PERC-negative patients to truly make it a valid tool.

"Diagnostic Accuracy of Pulmonary Embolism Rule-Out Criteria: A Systematic Review and Meta-analysis"


  1. >Please don't justify further work-up just
    >because they fail PERC - it barely moves the
    >needle with its terrible specificity.

    Wo....-if you haven't already decided to work a patient up for PE before applying the PERC, the game is already lost. PERC is not a screen; it is a way to stop a work-up, not a way to decide who needs one. The justification for the further w/u is that the pt who you decided to work-up before PERC has not been ruled out. All the specificity tells you is in that in patient you have already started the w/u, when they have a postive PERC, they are not at greater risk than you first estimated.

    I think we are thinking along the same lines.

  2. PERC shouldn't be misapplied to mandate further testing -- it's the same as ordering D-dimers on patients who are too low risk to deserve a workup.

  3. I have got to defend the usefulness of sitrep here
    with Pro and louder enemy footsteps it is incredibly handy, especially when a sniper and you hear someone sneaking up on you. And I used to play hardcore a lot [where everyone just camps:( ] but it became amazingly handy due to the lack of a grenade indicator. I must say that it has saved my life (and k/d) numerous times, while also getting me a few kills shooting claymores through walls :P


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