The shift to primary care expected in the initial ‘diagnostic’ management of cases of venous thromboembolism is indeed welcome. A recent article in the BJGP highlighted the role of D-dimer in reducing referrals for radiological imaging.1 However, one of the messages that needs to be stressed in this context is the importance of clinical probability scoring system. It is important that the primary care physicians do not over-rely on the D-dimer, and clinical evaluation should be considered as the first step. Reliability on the D-dimer in isolation can have problems especially since there is evidence in the literature for thromboembolic episodes occurring in the context of normal D-dimer.2,3
There are several possible explanations for a normal D-dimer even in the presence of venous thromboembolism. The levels of D-dimer increase in the circulation due to the breakdown of the fibrin-bound clots. Very often, individuals present with symptoms of lower limb thrombosis many days after the onset of symptoms. The clot breakdown in these cases may have ceased by the time they arrive for medical attention and the result would be a normal D-dimer. Second, in the patients who receive anticoagulation treatment sometimes before the hospital assessment is undertaken (patients who have problems with transport, or from the hospice, started on anticoagulation empirically), inhibition of clot lysis can cause normal D-dimer. This phenomenon has been noted to occur within 24 hours after receiving heparin therapy.4 It is also important to bear in mind that a normal cut-off of D-dimer is arbitrary and may not be applicable to every individual, since the clot-breakdown capacity varies between individuals. This is exemplified by the report in pregnancy of deep vein thrombosis and normal D-dimer.3 Last, there is the issue of wide variability between many different D-dimer assays.5 Each caregiver should take into consideration the appropriate cut-off suited for the assay and setting before they can attribute a level useful in exclusion of thrombosis.
In summary, there is no alternative to good clinical assessment in the exclusion of venous thromboembolism and D-dimer level is only a useful adjunct.
- © British Journal of General Practice 2012
