Renal function dynamics in COVID-19: exploring biomarker interactions with D-dimer and C-reactive proteins.

COVID-19, caused by the SARS-CoV-2 virus, is mainly recognized for its respiratory manifestations. However, growing evidence regarding the widespread expression of ACE2 and TMPRSS2 receptors on diverse extrapulmonary sites, particularly in renal tubular epithelial cells, suggests susceptibility of other organ systems, including the kidneys, to such conditions as acute kidney injury (AKI). In the present retrospective study, we explored the interrelationship between disease severity and renal function abnormalities by analyzing key biochemical parameters: blood urea nitrogen (BUN), serum creatinine (Cr), the BUN/Cr ratio, and estimated glomerular filtration rate (eGFR). Using descriptive statistics and joint generalized linear models, we examined both the mean and variance components of these markers alongside inflammatory indicators such as C-reactive protein (CRP) and D-dimer. Our findings revealed a significant positive correlation between serum urea levels and both CRP and D-dimer concentrations, suggesting that elevated urea may reflect heightened inflammatory activity. Additionally, eGFR showed a positive association with CRP, indicating potential renal involvement in systemic inflammation. Our in silico studies supported such observations, as genes responsible for CRP and D-dimer elevation were found to be common in AKI-associated pathways, particularly IL-6/JAK-STAT, NF-κB, HIF-1, and complement pathways, ultimately causing renal microthrombosis, tubular necrosis, and fibrotic remodeling. Notably, serum Cr revealed no significant association with CRP or D-dimer, possibly due to its lower sensitivity in early renal dysfunction. Although the study is limited by a relatively small sample size and lacks longitudinal data, it underscores the importance of monitoring renal function parameters in COVID-19 patients as potential markers of disease progression.