COVID-19, caused by the new coronavirus SARS-CoV-2, exhibits a broad spectrum of clinical manifestations. Various markers have been investigated to identify factors contributing to disease severity and prognosis. Among these, alterations in the neutrophil-to-lymphocyte ratio (NLR) have been considered crucial in the disease pathophysiology and studied as potential biomarkers for disease severity and prognosis. This study aimed to assess the NLR in patients with COVID-19 and its association with disease severity.

Blood samples were collected from 55 adults diagnosed with COVID-19. Statistical analyses were performed using IBM SPSS Statistics 20 software with a significance level set at 0.05. We utilized the Chi-Square test to examine associations between female and male biological sex and changes in neutrophil and lymphocyte values. The multinomial logistic regression test was applied to investigate associations between COVID-19 severity and neutrophil and lymphocyte values. Additionally, one-way ANOVA was conducted to assess the association between NLR means and COVID-19 severity.

The study group consisted of 41 women (74,5%) and 14 men (25,4%), aged between 18 and 61 years, with a mean age of 31,4. When comparing sex with NLR alterations, we found differences (p < 0.01). Neutropenia was observed in mild and moderate cases, with a higher prevalence in the latter (25,4%), and significant differences in cases of mild COVID-19 severity (p < 0.05) compared to the normal neutrophil count. Lymphocytopenia was identified in mild cases (7.3%), while lymphocytosis occurred in moderate cases (5.4%), with differences in lymphocytosis between mild cases of the disease (p < 0.05). The NLR was higher than 3.5 in mild cases and intermediate (between 2 and 3) in severe cases. The overall NLR mean was 1.5, with 3.3 for females and 2 for males. We found no differences in NLR means concerning disease severity (p = 0.77). However, NLR exhibited an association with males in moderate and severe cases, and with females in mild cases (p < 0.05).

The proportional increase in neutrophils according to COVID-19 severity suggests immune system activation, possibly in response to cytokines that promote neutrophil migration to the infection site. The lymphocyte count shows an inverse relationship with disease severity, with higher counts in mild cases and lower counts in severe cases. The presence of neutropenia in mild and moderate cases may be attributed to the lack of hematological data in individuals with more severe disease. Reduced lymphocyte count may indicate immune system suppression, consistent with lymphopenia in mild cases. Studies have reported elevated NLR in severe cases, although most of our severe cases lacked hematological data for comparison.

The study's findings strengthen the link between increased inflammation and the severity of COVID-19. The NLR proves to be a relevant indicator, as its elevation is associated with a higher risk of mortality in COVID-19 patients, making it essential for clinical management and prognosis assessment of disease severity.