Well’s, PERC, PESI and more: using the right score on the right patient in the right scenario
Pulmonary Embolism is kind of like Lupus and Sarcoid … no seriously! If you think about it, it’s almost never wrong to have these diagnoses on your differential given the right set of signs/symptoms.
Unfortunately, this means that we’re left deciding whether PE needs to be pursued, ruled out, or cast aside. Enter the three most common calculators used when dealing with PEs, Well’s, PERC, and PESI.
There is probably at least one Well’s score calculated every day in our hospital, but I’m willing to bet that more often than not we’re using it WRONG. Well not any more! In this post we lay out the correct way to evaluate risk of PE using Well’s Criteria (with more posts to come on PERC and PESI).
Well’s Criteria for Pulmonary Embolus
What is the Well’s Criteria/Score?
Well’s Criteria is a RISK STRATIFICATION SCORE and CLINICAL DECISION RULE designed to estimate the probability of acute PE in those patients in which history and examination SUGGEST PE AS A DIAGNOSTIC POSSIBILITY. The score can be interpreted using 2 different risk schema (2-tier and 3-tier), and is thus meant to inform decisions about the need for further work-up.
When should I use it? What question am I trying to answer?
The original intent of the tool as outlined in the 2001 paper by Wells et al in which it first appeared was to identify the patients in whom the risk of PE was so low that the diagnosis could be confidently ruled out by obtaining a negative D-dimer without CT: in my patient, is the probability of PE low enough for me to rule out PE as a diagnosis without using CT Angiography?
How do I correctly use the Well’s Score? What do I do next?
The Well’s Score can be interpreted using 2 and 3-tier models to inform clinical decision-making, guidelines appear to favor the two tier model which utilizes only the high sensitivity d-dimer and more conservative risk stratification; “intermediate” risk patients are thought to be still too high risk to be evaluated without further risk stratification.
Three Tier Model
- Patient is determined to be low risk (<2 points:1.3% incidence PE): consider d-dimer
testing to rule out Pulmonary embolism. Alternatively consider a rule-out
criteria such as PERC.- If the dimer is negative consider stopping workup.
- If the dimer is positive consider CTA.
- Patient is determined to be moderate risk (score 2-6 points, 16.2% incidence of PE):
consider high sensitivity d-dimer testing or CTA.- If the dimer is negative consider stopping workup.
- If the dimer is positive consider CTA.
- Patient is determined to be high risk (score >6 points: 37.5% incidence of PE):
consider CTA. D-dimer testing is not recommended.
Two Tier Model
- Patient risk is determined to be “PE Unlikely” (0-4 points, 12.1% incidence of PE):
consider high sensitivity d-dimer testing.- If the dimer is negative consider stopping workup.
- If the dimer is positive consider CTA.
- Patient risk is determined to be “PE Likely” (>4 points, 37.1% incidence of PE):
consider CTA testing.
What else should I consider when using Well’s in real life?
Dr. Well’s says it best on the MDCalc Web site. “The model should be applied only after a history and physical suggests that venous thromboembolism is a diagnostic possibility. it should not be applied to all patients with chest pain or dyspnea or to all patients with leg pain or swelling. This is the most common mistake made. Also, never never do the D-dimer first [before history and physical exam]. The monster in the box is that the D-dimer is done first and is positive (as it is for many patients with non-VTE conditions) and then the physician assumes that VTE is now possible and then the model is done. Do the history and physical exam first and decide if VTE is a diagnostic possibility!”
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