Evaluating patients with pulmonary thromboembolism: a retrospective study on the utilization of serum D-dimer assay and CT angiography

Author(s): Amar Richard Tobias*, Anjali Agrawal & Arjun Kalyanpur

Background and objective: Serum D-dimer assay is an inexpensive laboratory test with a high negative predictive value, obviating the need for computed tomographic pulmonary angiography (CTPA) in patients with low clinical probability of thromboembolic disease. It has been recommended that CTPA may be performed only in patients with positive D-dimer assays and clinical suspicion of PTE (pulmonary thromboembolism), to curb unnecessary imaging and health care costs. We wanted to reassess the validity of this recommendation by looking into the D-dimer results in patients with positive PTE on CTPA. Methods: All patient records with positive PTE diagnosis on CTPA and having relevant laboratory data during one calendar year (January 01 to December 31, 2009) were selected. Serum D-dimer values of >500 ng/ml was considered abnormal. The D-dimer results among the patients who had the test performed were tabulated based on age and sex along with those without D-dimer assay in the same groups and correlated with their percentage distribution. Results: Out of a total of 98 positive PTE cases on CTPA, only 26 patients (26.5%) had a serum D-dimer assay done prior to CTPA. Of these, 20 (76.9%) had elevated values and 6 cases (23.1%) had a negative test. Negative D-dimer results varied with patient age, being highest in the 21-40 years age group. Conclusion: Overall, there seems to be more preferred use of CTPA and underutilization of serum D-dimer assay in clinical practice for suspected PTE. Secondly, negative D-dimer assay should not be used to triage patients with a high clinical index of suspicion for PTE.

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