Monocyte Distribution Width as a Pragmatic Diagnostic Screen for SARS-CoV-2 and Influenza Infection

Background: Monocyte distribution width (MDW) is a novel marker of monocyte activation, which is known to occur in the immune response to viral pathogens. Our objective was to determine the diagnostic performance of MDW and other leukocyte parameters for SARS-CoV-2 and influenza infection. Methods This was a prospective cohort analysis of adult patients who underwent complete blood count (CBC) and SARS-CoV-2 or influenza testing in an Emergency Department (ED) between January 2020 and July 2021. The primary outcome was SARS-CoV-2 or influenza infection. Secondary outcomes were measures of severity of illness including inpatient hospitalization, critical care admission, hospital lengths of stay and mortality. Descriptive statistics and diagnostic performance measures were evaluated for monocyte percentage, MDW, white blood cell (WBC) count, and neutrophil to lymphocyte ratio (NLR). Results 3,425 ED patient visits were included. SARS-CoV-2 testing was performed during 1,923 visits with a positivity rate of 5.4%; influenza testing was performed during 2,090 with a positivity rate of 2.3%. MDW was elevated in patients with SARS-Cov-2 (median 23.0U; IQR 20.5–25.1) or influenza (median 24.1U; IQR 22.0-26.9) infection, as compared to those without (18.9U; IQR 17.4–20.7 and 19.1U; 17.4–21, respectively, p < 0.001). Monocyte percentage, WBC and NLR values were within normal range in patients testing positive for either virus. MDW identified SARS-CoV-2 and influenza positive patients with an area under the curve (AUC) of 0.83 (95% CI 0.79–0.86) and 0.83 (95% CI 0.77–0.88), respectively. At the accepted cut-off value of 20U for MDW, sensitivities were 83.7% (95% CI 76.5–90.8%) for SARS-CoV-2 and 89.6% (95% CI 80.9–98.2%) for influenza, compared to sensitivities below 45% for monocyte percentage, WBC and NLR. MDW negative predictive values were 98.6% (95% CI 98.0-99.3%) and 99.6% (95% CI 99.3–100.0%) respectively for SARS-CoV-2 and influenza. Conclusions Monocyte Distribution Width (MDW), available on a routine complete blood count (CBC) with differential, is sensitive and specific for the early detection of SARS-CoV-2 and influenza infection.