Effectiveness of D-dimer level for screening pulmonary embolism in COVID era: a single institution experience

Introduction: The plasma D-dimer level is used as a screening test for thrombosis or embolism. Patients with pulmonary embolism (PE) are expected to have a high D-dimer level in nearly all cases. D-dimer levels are also increased normally with physiological needs with age and pregnancy. Cancer and COVID-19 have also been associated with higher D-dimer level. Thus, the aim of this study was to evaluate D-dimer effectiveness for screening pulmonary embolism during the COVID era depending on the patient age, cancer history and COVID-19 status.

Methods: This is a retrospective observational study performed at the Hôpital de la Cité-de-la-Santé de Laval (Canada). Between March 1st and June 30th 2020, 1080 consecutive patients underwent diagnostic imaging procedure to exclude PE. Of which, 412 patients had SPECT VQ and 668 had CTPA. Three hundred and twenty-eight (328) patients with a positive diagnostic exam for PE, a COVID-19 testing and a D-dimer level measured within three days of the imaging procedure were included in this study. Patient demographics, COVID-19 status and image findings were documented. Student t-test was used to compare data.

Results: Thirteen percent (13%, n=41) of the cohort was diagnosed with pulmonary embolism, 18% (n=59) of the cohort was tested positive for COVID-19 and 50% (n=163) was older than 65 years old. The mean value of D-dimer level is 6.1 ug/mL and 1.7 ug/mL for PE+ and PE- patients respectively (p < 0.05). For PE+ subgroup, patients tested positive for COVID-19 (C+) had a mean level of 7.8 ug/mL while patients with negative COVID-19 test (C-) had a value of 5.5 ug/mL (p < 0.05). In the same subgroup with PE+, the mean D-dimer level is of 6.6 ug/mL for patients over 65 year old and 5.0 ug/mL for patients under 65 years old (p = NS). In the same subgroup with PE+, the mean D-dimer level is of 5.0 ug/mL for patients with cancer history and 5.9 ug/mL with unknown cancer (p = NS). The diagnostic sensitivity of D-dimer for PE in the whole cohort is 95% and the specificity is very low at 15%. The sensitivity and specificity for PE diagnosis was respectively of 93% and 7% for patients over 65 years old (n=163) and, 100% and 23% for patients less than 65 years old (n=165).

Conclusions: D-dimer level is excellent for the exclusion of pulmonary embolism because of its high sensitivity. Patients with PE who had a positive COVID-19 test or older than 65 years, were more likely to have higher D-dimer level. Known cancer history did not affect the D-dimer level in our subgroup analysis. Because of the very low specificity of D-dimer, an imaging technique is necessary to confirm pulmonary embolism in all these subgroups despite their COVID status, age or cancer history.