The aim of our study was to evaluate the influence of asymptomatic infection and the occurrence of symptomatic COVID-19 on specific biochemical, renal, and immune parameters-renalase, neutrophil gelatinase-associated lipocalin (NGAL) cystatin C (CysC), and creatinine-and their weekly fluctuations during a one-month observation period in COVID-19 patients admitted to hospital. The study involved 86 individuals: 30 patients with diagnosed COVID-19, 28 people with asymptomatic infection confirmed with IgG antibodies-the IG(+) group-and 28 individuals without any (IgG, IgE) anti-SARS-CoV-2 antibodies-the IG(-) group. In the COVID-19 group, blood was drawn four times: (1) on day 0/1 after admission to hospital (C1 group), (2) 7 days later (C7 group), (3) 14 days later (C14 group), and (4) 28 days later (C28 group). In the IG(-) and IG(+) groups, blood was drawn once. There were no significant differences in creatinine, Cys C, and uric acid between any of the analyzed groups. NGAL levels were significantly higher in IG(+) and at all time-points in the COVID-19 groups than in controls. A similar observation was made for renalase at the C7, C14, and C28 time-points. Plasma renalase, NGAL, and CysC are unrelated to kidney function in non-critically ill COVID-19 patients and those with asymptomatic infection. Renalase and NGAL are most likely related to the activation of the immune system rather than kidney function. Asymptomatic SARS-CoV-2 infection causes a rise in plasma NGAL levels similar to those observed in symptomatic COVID-19 patients. Therefore, more attention should be paid to tracking and monitoring the health of these people.
Keywords: COVID-19; NGAL; SARS-CoV-2; cystatin C; renalase.