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Figure: acute PE, sickle cell disease, SCD, venous thromboembolism, VTE, vaso-occlusive crisis, acute chest syndrome, D-dimer testing, CTPA, ACS, radionuclide scanning, V/Q scan
BY EMEDHOME.COM
The incidence of venous thromboembolism in adult patients with sickle cell disease (SCD) is high; up to 12 percent of patients with SCD have a VTE by age 40. (Cureus. 2022;14[8]:e28528; https://bit.ly/3T6fAKy; Blood. 2018;132[17]:1761; http://bit.ly/3mKcFeF.)
Complicating this issue is that patients with SCD have overlapping symptoms between PE and vaso-occlusive crisis and acute chest syndrome that lead to diagnostic challenges. (Br J Haematol. 2022;198[3]:e42; https://bit.ly/3mDmBGB.) Emergency physicians also need to be aware that the typical diagnostic approach to PE may not apply to SCD patients.
D-dimer testing does not have a clear role in diagnosing VTE in SCD. Using D-dimer levels to exclude VTE in SCD patients is unreliable, given baseline elevations even when patients are clinically well due to the continuously activated coagulation cascade. (Cureus. 2022;14[8]:e28528; https://bit.ly/3T6fAKy; Blood. 2018;132[17]:1761; http://bit.ly/3mKcFeF; Br J Haematol. 2022;198[3]:e42; https://bit.ly/3mDmBGB; Am J Respir Crit Care Med. 2011;184[9]:1022; https://bit.ly/3T6rUuo; J Nucl Med. 2018;59[8]:1255; http://bit.ly/3l5mOSA.)
Because normal D-dimer levels are rather unusual in SCD patients, the physician usually proceeds to imaging if there is concern for acute PE. (Blood. 2018;132[17]:1761; http://bit.ly/3mKcFeF.)
CTPA findings may be inaccurate in SCD patients because the filling defects visualized may represent the high prevalence of in situ pulmonary thrombosis in ACS patients. (Cureus. 2022;14[8]:e28528; https://bit.ly/3T6fAKy; Blood. 2018;132[17]:1761; http://bit.ly/3mKcFeF; Am J Respir Crit Care Med. 2011;184[9]:1022; https://bit.ly/3T6rUuo; J Nucl Med. 2018;59[8]:1255; http://bit.ly/3l5mOSA.) Even in the absence of ACS, it is possible that subsegmental (or smaller) filling defects on CTPA may represent in situ sickling rather than a classic fibrin-rich clot.
Radionuclide scanning (ventilation/perfusion scan) is argued to be preferable for evaluating acute PE in SCD patients because it offers well-defined diagnostic criteria. (Cureus. 2022;14[8]:e28528; https://bit.ly/3T6fAKy; Blood. 2018;132[17]:1761; http://bit.ly/3mKcFeF; Am J Respir Crit Care Med. 2011;184[9]:1022; https://bit.ly/3T6rUuo; J Nucl Med. 2018;59[8]:1255; http://bit.ly/3l5mOSA.)
The V/Q scan also offers practical advantages over CTPA for diagnosing PE in patients with SCD, including minimizing radiation exposure and avoiding IV contrast. Reducing radiation exposure is particularly relevant for patients with sickle cell disease who are younger and more biologically susceptible to the ill effects of radiation exposure and whose lifelong chronic illness makes them more likely to develop significant kidney disease and undergo repeated imaging.
V/Q scanning is less useful in patients with pulmonary parenchymal abnormalities on plain chest radiographs, so institutional practice in many centers is to triage stable patients with normal chest radiographs to V/Q scan and those with abnormal radiographs to CTPA. (J Nucl Med. 2018;59[8]:1255; http://bit.ly/3l5mOSA.)
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