We read the article “Value of red blood cell distribution width (RDW) on emergency department (ED) admission in patients with venous thrombosis (VT)” by Lippi et al with interest. The investigators aimed to investigate the association between RDW and patients with VT including cases of superficial VT, deep vein thrombosis, and/or pulmonary embolism (PE). In the present study, the RDW values were found to be significantly increased in all cases of VT compared with controls. Furthermore, the investigators also found that RDW exhibited a significant diagnostic performance at ED admission, displaying an area under the curve of 0.65 (95% CI 0.62 to 0.68; p <0.001) for all cases of VT. In addition, the conventional cut-off value of 14.6% was characterized by 0.75 negative predictive value and 0.48 positive predictive value for all cases of VT. Finally, they suggest that increased RDW not only associated with VT but also increased the efficiency of baseline risk assessment of patients with suspected VT on ED admission. This study gives important outcomes on this clinically relevant condition.

RDW is a measure of the variability in the size of circulating red blood cells (RBCs) and is a derived from automated hematology analyzers. Increased RDW levels have been found to be associated with poor outcomes in patients with various diseases, such as organophosphate poisoning, acute pancreatitis, non–ST elevation acute coronary syndrome, contrast-induced nephropathy, deep vein thrombosis, ischemic stroke, mesenteric ischemia, PE, and many more. Potential mechanisms underlying the effect of increased RDW levels on these various diseases are not clear, subject to debate, and indeed complex. Yčas et al recently described a possible mechanism of persistent increase in RDW levels after acute and chronic diseases. According to a study, increased RDW levels have been postulated to the powerful stimulation of erythropoiesis by erythropoietin, a hormone synthesized mainly from the peritubular interstitial cells of the kidneys during hypoxic conditions, which promotes the release of enlarged RBCs from bone marrow. Finally, the presence of circulating enlarged RBCs disturbs RDW levels in hypoxic patients. However, in contrast to the previously mentioned study, hypoxemia leading to the release of a number of proinflammatory cytokines, which inhibits erythropoietin secretion and RBC maturation, thus enhancing anisocytosis. Another hypothesis is that elevated RDW may be due to a slight reduction of RBCs turnover. In contrast, a number of physiological conditions (e.g., pregnancy, aging, or physical exercise), pathologic conditions (e.g., iron, vitamin B12, folic acid deficiency anemia, hemolytic anemia, hereditary spherocytosis, congenital hemoglobin disorders such as thalassemia or hemoglobin variants), and use of some medications may impair erythropoiesis.

PE, the most dangerous and potentially life-threatening complication of VT, frequently presents atypically and is often a diagnostic challenge for emergency physicians. Several guidelines, risk stratification tools, and biomarkers have therefore been developed to make a prompt and correct diagnosis, to predict morbidity and mortality, safe management with outpatient anticoagulation, or hospitalization of patients with PE. Consequently, we now emphasize that, in the absence of other inflammatory biomarkers and risk stratification tools, RDW alone does not provide an appropriate representation of a patient’s global inflammatory status or prognosis.