Don't Always Depend on Your D-Dimer: An Atypical Case of Pulmonary Embolism

Abstract

Case: A 35-year-old female patient, with current IV drug use and a history of endocarditis warranting tricuspid valve replacement, presented with dyspnea and chest pain. On physical exam, she was found to have scattered wheezes on expiration with no shortness of breath or LE edema. As the Wells’ score for PE revealed a moderate risk, CTA and D-dimer were obtained. CTA revealed low contrast uptake in the right pulmonary artery, most concerning for a PE. D-dimer and coagulation studies were normal, making DVT unlikely and PE questionable. Therefore, there was high suspicion for endocarditis with septic emboli. On day two, TEE showed no valvular vegetations or thrombus. With no evidence of endocarditis, DVT was reconsidered. Bilateral LE doppler ultrasounds were negative for DVT. However, a repeat D-dimer was found to be elevated (596 ng/mL). Clinical impression on day three was a PE secondary to a small superior venous thrombosis from IV drug use. Conclusions: IV drug use is recognized as a risk factor for SVT and DVT due to endothelial damage of injected veins and/or increased coagulation factors. As a LE DVT was ruled out through ultrasound, this patient likely had an UE thrombus with a secondary PE. However, her low D-dimer in the setting of a PE is puzzling considering the test’s high sensitivity (95%). Given that her subsequent D-dimer was elevated, this suggests that the initial test may have been inaccurate. Clinical Significance: D-dimer is considered to be a useful test to rule out DVT and PE in cases of low or moderate probability. However, a few reasons for false-normal D-dimer have been elicited: small emboli, anticoagulant pretreatment, and symptoms ongoing for ≥ 10 days. In this case with moderate probability, the initial falsely low D-dimer decreased suspicion for thrombosis and was most likely due to small emboli. Therefore, the causes of false-normal D-dimer must be well known and considered in order to avoid misdiagnosis.