Age-adapted D-dimer cutoffs in older patients may help exclude DVT in primary care

Using age-adapted D-dimer cutoffs in older patients may help rule out deep venous thrombosis (DVT) in primary care, according to a new study.

Researchers in the Netherlands conducted a retrospective, cross-sectional diagnostic study involving patients of 110 primary care doctors affiliated with three hospitals. Patients were evaluated for clinical suspicion of DVT between Jan. 1, 2002, and Jan. 1, 2006. The study's main objective was to determine whether age-adjusted D-dimer values could be used to safely exclude suspected DVT in primary care patients. All patients were assessed using both the Wells score for clinical probability of DVT and D-dimer levels. The primary outcome measures were the proportion of patients whose D-dimer levels were below two proposed age-adapted cutoffs and in whom DVT could be safely excluded, as well as the number of false-positive results. The two proposed D-dimer cutoffs were age in years × 10 μg/L in patients older than 50 or 750 μg/L in patients 60 or older. The study results were published online June 6 by BMJ.

A total of 1,374 consecutive patients with clinically suspected DVT were included in the study. Of these, 936 (68.1%) were older than 50. Six hundred forty-seven patients had a low clinical likelihood of DVT according to the Wells score. In this group, the age-dependent cutoff value safely excluded DVT in 309 patients (47.8%) compared with 272 patients (42.0%) when the cutoff of 500 μg/L, the conventional value, was used (increase, 5.7% [95% CI, 4.1% to 7.8%]). The false-negative rates were 0.5% and 0.3%, respectively (increase, 0.2% [95% CI, 0.004% to 8.6%]). In patients older than 80 years, the age-dependent cutoff value safely excluded DVT in 22 patients (35.5%) compared with 13 patients (21.0%) using the conventional cutoff value (increase, 14.5% [95% CI, 6.8% to 25.8%]). The cutoff value of 750 μg/L had similar exclusion and false-negative rates when compared with the age-dependent cutoff value (47.4% [307 patients] and 0.3%, respectively).

The authors noted that some data on D-dimer levels were missing and that two different assays were used, among other limitations. They also suggested caution when interpreting their results in patients older than 80, since that subgroup was small. However, they concluded that when combined with a low clinical probability of DVT, the age-dependent D-dimer cutoff in patients older than 50 and the higher cutoff of 750 μg/L in patients 60 and older significantly increased safe exclusion of DVT compared with the conventional cutoff value in primary care. They called for further study to assess the potential benefits of this approach in daily practice before widespread implementation.