D-dimers as a screening test for venous thromboembolism in pregnancy: is it of any use?

In non-pregnant women, D-dimers are used successfully to aid diagnosis of suspected pulmonary embolus (PE), as they have high sensitivity, moderate specificity and high negative predictive value. However, D-dimer levels are physiologically raised in pregnancy and thus overlap the values normally associated with PE. The aim of this retrospective study therefore was to investigate the use of D-dimer levels as a screening test for suspected PE in pregnancy and to determine if a negative D-dimer level could exclude the diagnosis in pregnant women. A total of 37 women suspected of PE had both ventilation perfusion (VQ) scans and D-dimer levels performed. Thirteen were reported as having a low probability of PE following VQ scan, while 24 were thought to have a moderate or high probability of PE. Women who had a low probability of PE following VQ scanning were found to have D-dimer levels ranging from 0.25-2.2 mg/l, while women who had a high probability of PE following scanning had D-dimer levels ranging from 0.31-1.74 mg/l. The sensitivity and specificity of D-dimer as a test for suspected PE in pregnancy was calculated to be 0.73 and 0.15 respectively, while the negative likelihood ratio was 1.8. Current guidelines advocate the use of a negative D-dimer result to exclude the diagnosis of PE in pregnancy. However, this study suggests that D-dimer testing in pregnancy has a high negative likelihood ratio and should not be used. Larger prospective observational studies are required to collaborate the findings from this study.