RDW Levels Associated with Adverse Outcomes in COVID-19 Patients

The red cell distribution width (RDW) blood test measures the amount of red blood cell variation in volume and size. RDW is not used as an isolated parameter when interpreting a complete blood count (CBC); instead, it provides shades of meaning in the context of the hemoglobin (Hgb) and mean corpuscular value (MCV).

Increasing scientific evidence has shown that abnormalities in routine laboratory tests, particularly hematological tests, have the potential to indicate, in a quick, practical and economical way, the need for specific laboratory tests for the diagnosis of SARS-CoV-2 infection, besides assisting in the prognosis of the disease and in the optimization of its clinical monitoring.

Medical Scientists from several institutions including the Baim Institute for Clinical Research (Boston, MA, USA) performed a comprehensive literature search from inception to September 2020 to harvest original studies reporting RDW on admission and clinical outcomes among patients hospitalized with COVID-19. The study endpoint was adverse clinical outcomes, defined as the composite of mortality or severe COVID-19. A total of 14,866 patients from 10 studies were included in the meta-analysis. The mean age ranged from 38 to 77 years while the proportion of males ranged from 42.4% to 69.2%.

The investigators reported that the meta-analysis found that higher levels of RDW were associated with adverse outcomes in COVID-19 patients (mean differences, 0.72; 95% confidence interval [CI], 0.47-0.97; I², 89.51%). Further, results of the subgroup analysis showed that deceased patients had higher levels of RDW compared to survived patients (mean differences, 0.93; 95% CI, 0.63-1.23; I², 85.58%). Similarly, severely ill COVID-19 patients had higher levels of RDW, as opposed to patients classified to have milder symptoms (mean differences, 0.61; 95% CI, 0.28-0.94; I², 82.18%).

Jane J Lee, PhD, the first author of the study, said, “Emerging evidence has underscored the potential usefulness of RDW measurement in predicting the mortality and disease severity of COVID-19. As RDW is widely available and included as a routine parameter of complete blood count, this simple laboratory test can be particularly useful in the context of COVID-19 pandemic, where identifying high-risk patients and facilitating timely intervention with limited resources are critical.”

The authors noted that the exact pathophysiology behind the association between increased RDW and adverse outcomes has yet to be elucidated. Numerous reports have suggested that COVID-19 infection was associated with an increase in the release and production of white blood cell counts and platelets from the bone marrow. The stimulation to the bone marrow may also impact the red blood cell (RBC) kinetics, resulting in a wider range of RBC size and subsequently elevated RDW levels. The study was published on January 15, 2021 in the Journal of Medical Virology.

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Baim Institute for Clinical Research