It currently is not possible to diagnose all DVTs as it is a myth that there
is a gold standard investigation for diagnosis. At best venography wins the
bronze award as it is not possible to cannulate everybody a failure rate of
approx 20% is reported in the literature, secondly venography is an
iatrogenic cause of DVT reported in approx 3%.
Doppler ultrasound is used by many trust as the investigation of choice. The
problem with this is that below knee dvt cannot be accurately diagnosed and
is operator dependant. DVT the cause of PE in 90% of cases but only found in
50% of cases by doppler!
Venometry seems to be a useful screening tool it has similiar positive
prediction to d-dimers and has the advantage of testing the anatomical
location.
Therefore it does seem that d-dimer plays fourth fiddle and therefore can be
disregarded in dvt protocols although is an important test when excluding
PE- but remember less than 10% of the elderly will ever have a negative
d-dimer.
So the question in dvt is why do we need to diagnose dvt? If you want to
prevent post thrombotic symptoms in all concerned then you are unlikely to
succeed, however if you are only worried about pulmonary embolus than you
are concerned with diagnosing clinically significant disease and not all
dvts.
Therefore bin d-dimers.
Screen with venometry (strain gauge)
If positive doppler
If positive treat, if negative in venometry or doppler re-evaluate in 5-7
days.
In 3 years this has been successful in Brighton. But the importance is in
reviewing these patients and repeating tests serially.
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