This lecture focuses on the common condition known as pulmonary embolism.

And I think a reasonable place to start is to talk about D-Dimer testing.

Now, a D-Dimer becomes elevated when there's an acute thrombus.

Why?

Because the D-Dimers are a byproduct of the blood clot. Specifically, there is

fibrin within the clot and the breakdown products of these fibrinous blood clots is the

D-dimers. So if you don't have elevated D-dimers in the plasma, you can pretty much exclude the possibility

that there is a major blood clot like a big PE going on.

On the other hand, having an elevated D-dimer does not at all mean that you have a DVT or a P-E. Why? Because the elevated D-dimer happens in any type of blood clot.

So if you have a patient that fell down the stairs and fractured their hip and now they're short of breath,

do you want to get a D-dimer? No, because it's going to be elevated. Likewise,

patient just gets out of surgery. Is the D-dimer going to be elevated? Of course it is.

And there's a bunch of other disorders and conditions that the D-Dimers are going to be elevated

in. So other thromboembolic diseases, like a big stroke, is going to have an

elevated D-Dimer, but so well conditions like disseminated intravascular coagulation or severe

sepsis. But D-dimer can be even elevated in a normal pregnancy, and of course it can be

elevated also in preeclampsia and eclampsia.

Therefore, it is very important to know the population you are ordering a test in and don't order

if it doesn't make sense to order it in that population. Because a D-dimer is not specific. It only helps you rule out a pulmonary embolism or a DBT, and there are even

exceptions to that rule. You see, D-Dimer tests should be used in combination with a pre-test

clinical probability assessment. And that is where it can be very helpful, because if you have a pre-test clinical probability assessment.

And that is where it can be very helpful.

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