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Peripheral blood lymphocyte-to-monocyte ratio as a screening marker for influenza infection
  1. Bijal Patel1,
  2. Monique Oye1,
  3. Daniel Norez2,
  4. Carmen Isache3
  1. 1Internal Medicine, University of Florida Health, Jacksonville, Florida, USA
  2. 2Center for Data Solutions, University of Florida Health, Jacksonville, Florida, USA
  3. 3Infectious Disease, University of Florida Health, Jacksonville, Florida, USA
  1. Correspondence to Dr Bijal Patel, Internal Medicine, University of Florida Health, Jacksonville, FL 32209, USA; Bijal.Patel{at}


Influenza outbreaks occur annually and account for significant morbidity and mortality. The overall burden of influenza infections, in the USA, for the 2017–2018 season, was an estimated 45 million cases, 810 000 hospitalizations and 61 000 deaths. Literature suggests that leukocyte count and differential, particularly lymphopenia and/or monocytosis, can provide diagnostic value for influenza infection. However, studies regarding these findings are limited in the adult population, particularly in the USA. The objective of this study was to determine if lymphocyte-to-monocyte ratio (L:M)<2 can be used as a screening marker for influenza infection. We performed a retrospective analysis of all patients who presented to University of Florida Health, Jacksonville, a university-affiliated tertiary care center in Jacksonville, Florida, between January 2017 and December 2018, with ‘influenza-like’ symptoms and who were subsequently admitted to the hospital. Patients were divided into two cohorts, based on whether they had laboratory-confirmed influenza versus another confirmed upper respiratory tract viral infection (influenza-like illness (ILI)). L:M was compared between the two groups and was found to be lower in the influenza group compared with the ILI group (p<0.0001). Results of this study demonstrate that a L:M<2 has significant diagnostic value in the acute phase of influenza and can be used for earlier detection and management of this disease, in order to improve clinical outcomes.

  • lymphocytes
  • hematologic tests
  • respiratory tract diseases

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  • Contributors BP and MO contributed equally in conceptualization, design of work, data acquisition, drafting and revising of the manuscript. DN contributed with statistical analysis and interpretation of data obtained. CI was the supervising, attending for the study and contributed in the design of work, writing and final editing of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval Approval from the University of Florida College of Medicine Institutional Review Board was sought prior to the initiation of the study.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information. Data were obtained via Epic EMR and stored in Redcap. Patient’s were de-identified prior to collection and storage of data.