D-dimer testing in pregnant patients: towards determining the next 'level' in the diagnosis of deep vein thrombosis

The role of D-dimer in excluding deep vein thrombosis (DVT) in pregnancy is currently uncertain. We hypothesized that the specificity of sensitive D-dimer assays could be improved without compromising sensitivity by using higher D-dimer cut-off values.

To determine the test characteristics of two rapid enzyme-linked immunosorbent assays and three latex agglutination assays in pregnancy.

We recruited consecutive pregnant women who presented to participating centers with suspected DVT for the study. Symptomatic women were investigated with compression ultrasonography, and received 3 months of clinical follow-up to assess for the presence of venous thrombosis. Plasma samples for D-dimer were collected and frozen at the time of presentation. The median and mean D-dimer values for respective trimesters of pregnancy in patients with and without DVT were calculated. Receiver operating curves (ROCs) were plotted for respective assays to establish the best cut-points. The test characteristics corresponding to standard cut-points and these 'pregnancy' cut-points are presented.

The prevalence of DVT in our cohort was 6.6% (95% confidence interval 4.0-10.6%). The mean and median D-dimer values were significantly increased throughout pregnancy. Overall, women with confirmed DVT had higher D-dimer levels than women without DVT (P < 0.0001). Improved specificities (62-79%) were observed with the use of higher cut-points obtained from ROCs for all five assays, and high sensitivities were maintained (80-100%) for DVT diagnosis.

Using higher cut-points than those used in non-pregnant patients, the specificity of D-dimer assays for the diagnosis of DVT in pregnancy can be improved without compromising sensitivity. Validation in prospective management studies is needed.