Do remember that the specificity and sensitivity depends on which d-dimer
test you use -they are not all the same. To evaluate the test for your
clinical enviroment you need to look at the literature relating to the same
brand of test and not generic or manufacturers figures. There may be
practical reasons why a unit uses one test with a drop in sensitivity eg a
point of care test for speed versus a lenghthy lab test or when the lab does
not have the equipment to do the test at all.
Katherine Henderson
Consultant in A&E Homerton Hospital London
----- Original Message -----
From: Sam Waddy <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, June 07, 2000 8:28 PM
Subject: Re: D-dimers in PE
> In message <[log in to unmask]>, Lawrence H
> Jaffey <[log in to unmask]> writes
> >I know the 'evidence' stacks up in favour of D-dimers, and I know that
> >'anecdotal' evidence just isn't good enough, but believe me, you can't
beat
> >an on-your-doorstep case like this colouring your view of how things
should
> >be done!!
> >
> >Lawrence Jaffey
> >Liverpool
> We had a recent (excellent) teaching session from on of the
> haematologists explaining the correct use of the Ddimer as they have set
> it up at the JRH:
> Basically my interpretation a few weeks down the line and how I now use
> them is: suspected PE/DVT: D Dimer is useful for its negative predictive
> value if your suspicion for PE/DVT clinically is low to moderate. When
> analysing the population of patients for whom the clinical suspicion is
> HIGH then the negative predictive value plummets, and therefore should
> not be used.
>
> We have a brief scoring chart on the wall at work, I am sorry I can't
> remember the reference, but scores factors like recent surgery,
> immobility, previous DVT, unilateral swollen leg, malignancy as +1 and
> the existence of an alternative diagnosis as -2 a score of >2 equals
> high probability (this scoring system apparently turns us beginners'
> predictive judgement into the equivalent of having a few years'
> experience and judgement).
>
> So: D Dimer has a good negative predictive value when used in those with
> low to moderate probability.
> D Dimer is of no real use if your clinical suspicion is high (but then
> VQ isn't great either)
> D Dimer has no real positive predictive value.
>
> --
> Sam Waddy
> A&E SHO Oxford
>
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