The role of serum lactate level in monitoring disease severity of Covid-19 pneumonia

Introduction: COVID-19, which emerged in China in December 2019, has affected millions of people worldwide. The clinical course of COVID-19 can vary from asymptomatic to fatal. COVID-19 pneumonia leads to tissue hypoxia and lactate production through aerobic glycolysis, which is the cellular response to provide immunological support. Higher lactate levels are expected in more severe cases. In this study, we aimed to investigate the role of serum lactate levels in monitoring the severity of COVID-19. Materials and Methods: The study was conducted between January 2020 and December 2022 in intensive care units, wards, and outpatient clinics of Ankara City Hospital. Ethical approval was obtained from the Ankara City Hospital Ethics Committee. A total of 150 patients who had follow-up visits at 1 and 3 months and for whom follow-up parameters were available were included in the study. Patients were categorized into three groups based on the severity of COVID-19: mild, moderate, and severe (severe-critical). LDH (lactate dehydrogenase), ferritin, CRP, and lymphocyte levels were measured during hospitalization and at 1 and 3 months. Pulmonary function tests including SFT, DLCO, and 6MWT were performed at 1 and 3 months. Dyspnea level was evaluated using the Borg scale. The serum lactate levels measured at 1 and 3 months were compared with the aforementioned parameters. Results: Of the 150 included patients, 67,3% (n=101) were male and 32,7% (n=49) were female. The age range was 29-83 years, with a mean age of 56,74±11,10 years. Additional comorbidities were present in 64,7% of the cases, including 6% with COPD, 11,3% with asthma, 1,3% with ILD, and 1,3% with malignancy. Among the patients, 46,7% (n=70) had severe, 37,3% (n=56) had moderate, and 16% (n=24) had mild disease. Significant differences were observed in serum lactate, LDH, ferritin, CRP, lymphocyte levels, borg scale, FEV1, DLCOc, and 6MWT between the measurements at 1 and 3 months (p<0.001). There was a significant difference in serum lactate values at 3 months between patients with mild, moderate, and severe disease (p<0.05). Negative correlations were found between serum lactate values at 1 month and saturation and DLCOc percentages at 1 month. As the saturation percentage and DLCOc levels increased, serum lactate values at 1 month decreased. Positive correlations were observed between serum lactate measurements at 3 months and admission ferritin, admission LDH, ferritin at 1 month, ferritin at 3 months, LDH at 3 months (respectively r=0,359, r=265, r=0,250 r=0,257 r=0,188), and negative correlations with admission lymphocyte levels, saturation percentage at 1 month, and borg scale at 3 months (respectively r=-0,202, r=-0,176, r=-0,213). Conclusion: Our study revealed a significant relationship between serum lactate levels at 3 months and the severity of COVID-19. Furthermore, significant correlations were found between serum lactate levels measured at 1 and 3 months and laboratory parameters and functional tests used in disease monitoring. Based on these analyses, it has been concluded that serum lactate levels in bacterial and viral infections, which may cause similar effects as COVID-19, could serve as an indirect prognostic marker in assessing the severity of the disease and monitoring its progression specifically in the context of COVID-19. Keywords: COVID-19, lactate, COVID-19 severity, pneumonia, prognosis