Age Adjusted D-dimer Cut Offs

This paper recently published trying to confirm if it’s OK to raise the d-dimer cut off in older people.

“Age-Adjusted D-Dimer Cutoff Levels to Rule Out Pulmonary Embolism: the ADJUST-PE Study.” 311, no. 11 (March 19, 2014): 1117–1124. doi:10.1001/jama.2014.2135. PMID 24643601

Hopefully you’ve heard about this already through ER Cast and over on BoringEM (if you want more discussion on d-dimer, then be sure and check out the LITFL page on it.) Basically if you’re over 50 then your new d-dimer cut off is 10 times your age. These guys tested that approach.

METHODS

• prospective data on pts with suspected PE from Europe.
• Stratified to low or high risk
• D-dimers were sent on the low risk ones and if -ve work up was finished. If +ve they went for CTPA
• follow up at 3 months by phone
• 3 blinded ‘experts’ adjudicated if something bad happened to them

RESULTS

• 3300
  • 2900 were ‘non-high’ probability and went down the d-dimer path
  • 400 were high and went straight to scan
• 330 fell into the ‘age adjusted’ level and all of these guys (who previously would have got advanced imaging) seemed to do well (for what that’s worth)
• of note their overall rule in rate for PE was 20%, much higher than many contemporary studies

THOUGHTS

We all want ways to rule out PE and avoid the CT scans. This might be another way to safely rule patients out, though it’s worth bearing in mind that it’s only going to affect a small number of patients.

This is by no means a perfect study. The group of interest did not actually get the reference diagnostic test (the CTPA) so we’re dependent on the veracity of their follow up to know if it’s truly OK to pursue this new strategy of age-adjusted cut off and forgo more advanced testing. This is a common problem in studies like this (see the Perry CT for SAH article as a great example of controversy over this very issue) and it doesn’t mean that it’s all nonsense but as always be sure to use your noodle when thinking about it.

Update:
Salim over at REBEL EM has a great post on this summarising the evidence for age adjusted d dimers. There’s actually a lot more evidence than I thought on this.

[Image Credit: Wikimedia Commons]