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ERCAST


Welcome to ERCast, a focused discussion on the questions, quagmires and known unknowns we face everyday in the emergency department.

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Oct 2, 2012

There is no perfect way to rule out pulmonary embolism. But what if we could change the game and move the d-dimer cutoff higher in the low risk patient? From 500 ng/ML to 1000ng/mL. You’d think that the specificity of the test would improve - fewer false positives. But what would we sacrifice in sensitivity? Would we start missing PE’s? On this episode of ERcast, we’ to talk about  doing just that - raising the d-dimer threshold in low risk patients. The idea for raising the d-dimer threshold comes from an article by Jeff Kline et al  in the April 2012 Journal of Thrombosis and Hemostasis titled  D-dimer threshold increase with pretest probability unlikely for pulmonary embolism to decrease unnecessary computerized tomographic pulmonary angiography

By the numbers...what happens when we raise the d-dimer threshold? Sensitivity decreases and specificity increases.

Using a d-dimer cutoff of <500ng/mL

Wells Score ≤4

  • Sensitivity   96.8%
  • Specificity   18.5%
  • Posterior Probability   3.8%

Revised Geneva Score ≤6

  • Sensitivity   96.8
  • Specificity   19.2
  • Posterior Probability   3.6

Using a d-dimer cutoff <1000 ng/mL

  • Sensitivity   90.5
  • Specificity   37.9
  • Posterior Probability   5.4

Revised Geneva Score ≤6

  • Sensitivity   91.3
  • Specificity   35.7
  • Posterior Probability   5.3

What should we take away from this paper? This was essentially a thought exercise in increasing the cutoff for a diagnostic test. It was not an outcome study. What happens when the d-dimer threshold  is  increased? Theoretically many fewer CTPAs (fewer patients exposed to radiation and risk of contrast induced nephropathy) and... more missed PEs. The question is one of balance. We know we do too many CTPAs. So, is a 1.5% (absolute) increased risk of missing PEs worth doubling the exclusion rate, or in other words, halving the number of CTPAs? It can be debated either way. What’s the right answer? There is no right answer. It’s complicated to understand ourselves. Some shared decision making with your patient may be in order.

 

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