Clinical Question: Pregnant patients who are suspected to have an acute DVT/PE present a diagnostic challenge. Can we use trimester-specific d-dimer thresholds to evaluate these patients?

Kovac, M et al. "The use of d-dimer with new cutoff can be useful in diagnosis of venous thromboembolism in pregnancy." European Journal of Obstetrics, Gynecology, and Reproductive Biology. January 2010. 148(1), 27-30:

• Kovac et al. followed 89 women without comorbidities throughout their pregnancy and showed that the mean d-dimer levels increased with pregnancy, decreasing the specificity of applying traditional d-dimer cut-offs from 82.4% to 32.6% to 1.1%, with each progressing trimester.

• Kovac et al. proposed higher trimester-specific d-dimer levels of 286, 457, and 644 ng/mL for the 1st, 2nd, and 3rd trimester based on the mean and standard deviations of d-dimer levels in his reference population.
• Kovac et al. also evaluated 12 women with clinical suspicion of VTE and found that VTE-proven d-dimer levels were above their suggested threshold.

Chan, W et al. "D-dimer testing in pregnant patients: towards determining the next "level" in the diagnosis of DVT." Journal of Thrombosis and Haemostasis. 2010. 8(5), 1004-1011:

• Chan et al. studied 228 pregnant women with clinical suspicion of DVT and measured their d-dimer levels with 5 different d-dimer assays and performed US scans to diagnose DVTs in the study population.
• Chan et al. compared the sensitivities and specificities of traditional d-dimer cutoffs with new cutoffs for pregnancy overall derived from their study population.
• Chan et al. found that 4 of the 5 assays improved specificity (61.2-78.8%) without significantly sacrificing sensitivity (93-100%).
• The authors propose the new cutoffs as "starting points" to be combined with pre-test probability and lower extremity duplex ultrasonography.
• The study was limited by small sample size, wide confidence intervals, and the use of stored plasma instead of blood obtained on presentation.

Conclusion: Both studies were limited by small sample sizes, and neither validated their proposed new cutoff levels. There is currently not enough evidence to promote the use of trimester-specific d-dimer thresholds.