A narrative review of red blood cell distribution width as a marker for pulmonary embolism.

Red blood cell distribution width (RDW) is a marker of variability in red blood cell size, and is routinely reported as part of a patient's complete blood count. RDW has been shown to be associated with the prediction, severity and prognosis of pulmonary embolism (PE) in recent studies. The underlying biomolecular mechanism of the relationship of RDW to PE is largely unknown, but is thought to be due to the relationship of RDW with acute inflammatory markers and variations in blood viscosity. This review substantiates that a high RDW level, defined using either an arbitrary number or according to receiver operator curve statistics, is associated with a higher risk of acute PE, increased severity (massive vs. submassive) of PE and increased mortality in patients with PE. Nevertheless, the comparison of current studies is limited due to the definition of high RDW (each study uses a different RDW cutoff level), the broad range of exclusion criteria and the inclusion of differing modalities used to diagnose a PE (computed tomography angiogram, ventilation-perfusion study, or clinical diagnosis). Despite the above limitations, these studies provide a promising future clinical use for RDW as a marker of PE.