D-Dimers

What is a D-dimer

- Protein fragment produced when a clot get dissolved

- Normally very low levels

- Clots are maintained or broken down from the equilibrium of plasmin vs fibrin causing clot stability or resolution

o   One of the final fibrin degradation production is D-dimer

o   Formation of clots cause a rise of D-dimer (clot in equilibrium between plasmin and fibrin so D-dimer made as fibrin is put down)

Sensitivity vs Specificity ?

-   D-dimer is highly sensitive for any fibrin degradation

o   clot formation and break down

o   vessel damage – autoimmune or infective

-   It is not specific for VTE

So being all Bayesian about it all to help with our differential based on the history

- But we can cheat. There are validated scoring systems that give us actual probability/risk stratifying

o   Wells for PE and DVT

-  These allow us to add extra validity to our own pre test probability/gestalt

Given the poor specificity of a D-dimer. A High pre-test probability ie high wells score means that we shouldn’t be doing a d-dimer but rather true diagnostic tests (US/CTPA/V/Q)