The doctoral thesis is based on a monothematic series of articles, which consists of a total of 4 works, including 3 original and 1 review work. The aim of this dissertation was to search for new markers of diabetic kidney disease (DKD) allowing for early diagnosis prior to the development of irreversible changes at the level of nephrons. In the course of the conducted research, in the group of diabetic patients, the biomarkers of both renal tubular damage: NGAL in urine and blood, KIM-1 in urine, uromodulin in blood serum and urine, and glomerular damage: albuminuria, transferrin and IgG in urine and CysC in blood serum, were examined. Diagnostic utility of the examined biomarkers in prediction of early stages of tubulopathy development associated with diabetes and renal glomerular damage before albuminuria was demonstrated, thus creating the possibility of using their index as new diagnostic tools aimed at early diagnosis of kidney damage in diabetes in its preclinical stage. The currently used nephroprotective treatment primarily affects renal glomerules, while the effect on the nephron tubules remains unclear. The presented finding forecasts a change in the diagnostics and treatment of patients at early-stage of DKD.