Neutrophil-to-Lymphocyte Ratio (NLR) and clinical outcome in COVID-19

Can a simple and inexpensive blood test predict how severe COVID-19 will be, and could this test be used as an early screening tool?

Clinicians are searching for a reliable prognostic marker that can distinguish patients at risk of developing more severe complications of COVID-19 to better manage resources and optimize treatment.

In the last few months, several studies were published regarding the use of the Neutrophil-to-Lymphocyte Ratio (NLR) and the clinical outcome in COVID-19.  Elevated age and NLR can be considered independent biomarkers for indicating poor clinical outcomes.

In March 2020, Chuan Qin and colleagues from Wuhan, China, published an article in Clinical Infectious Diseases that the novel coronavirus seemed to destroy lymphocytes (especially T-lymphocytes) needed to combat the virus effectively, so patients with a high NLR had a worse prognosis (study done on 452 patients with COVID-19).  Qin suggested that the Neutrophil-to-Lymphocytes Ratio be used as an early screening of critical illness as increased NLR levels reflect an enhanced inflammatory process and may suggest a poor prognosis.

Jingyuan Liu and colleagues also came to a similar conclusion “NLR is a predictive factor for early-stage prediction of patients infected with COVID-19 who are likely to develop critical illness.  Patients aged ≥ 50 and having an NLR ≥ 3.13 are predicted to develop critical illness and they should thus have rapid access to an intensive care unit if necessary.”

Another study was a small Italian study published in the International Journal of Antimicrobial Agents by Arturo Ciccullo and colleagues in May 2020.  The medical team studied the blood of 74 patients (51 males and 23 females) admitted to a hospital in Rome, Italy, in March 2020.  They noticed that when the number of neutrophils was four times or more than the number of lymphocytes (NLR), the patients were more likely to have a severe form of COVID-19 and had to be transferred to the ICU.  The medical team concluded that transfer to the ICU was predicted by an NLR of over four, whereas clinical improvement was predicted by younger age and a NLR below three.

In summary

Studies suggest that a simple and inexpensive blood test measuring the ration of two different kinds of white blood cells, neutrophil and lymphocyte cells, can be a useful tool to predict the clinical outcome of patients with COVID-19.

Although further studies with larger sample sizes will be needed to properly assess this matter, current studies show that NLR may be a rapid, widely available, useful prognostic factor in the early screening of critical illness in patients with confirmed COVID-19 to distinguish patients at risk of developing more severe complications of COVID-19 in order to better manage resources and optimize treatment.

References:

  1. Qin et al. Dysregulation of immune response in patients with COVID‐19 in Wuhan, China.  Intergovernmental Panel on Climate Change, ed. Clin Infect Dis. 2020; 53(9): 1‐ 30.
  2. Liu et al. Neutrophil-to-lymphocyte ratio predicts critical illness patients with 2019 coronavirus disease in the early stage.  J Transl Med (2020) 18:206.
  3. Cicculloa et al. Neutrophil-to-lymphocyte ratio and clinical outcome in COVID-19: a report from the Italian front line.  International Journal of Antimicrobial Agents, Available online 11 May 2020, 106017.
  4. Qu et al. Platelet‐to‐lymphocyte ratio is associated with prognosis in patients with Corona Virus Disease‐19.  Journal of Medical Virology, March 2020.
  5. Yang et al. The diagnostic and predictive role of NLR, d-NLR and PLR in COVID-19 patients.  Int Immunopharmacol. 2020 Jul; 84: 106504.
  6. Huang et al. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet. 2020; 395(10223): 497‐ 506.