**5. Conclusions**

In the present study, we evaluated six selected miRNAs (*miR-29c*, *miR-126*, *miR-146a*, *miR-150*, *miR-155*, and *miR-223*) and s-Uromodulin as biomarkers of kidney function in KTRs. The selected miRNAs and s-Uromodulin were compared not only with conventional GFR biomarkers (creatinine, cystatin, and estimated GFR), but also, as a novelty, with the radioisotope method, providing significant reinforcement to the credibility of the findings. To the best of our knowledge, this is the first study to compare these markers with the clinical gold standard of GFR (i.e., 51CrEDTA clearance) in KTRs.

In brief, the selected miRNAs are independent of kidney graft function, indicating their potential as biomarkers of associated etiopathogenesis of kidney graft disease processes. In contrast, s-Uromodulin is dependent on all observed parameters of kidney graft function. However, s-Uromodulin reliably reflects the early stages of kidney graft disfunction, in which conventional GFR-related biomarkers, including 51Cr EDTA, are still within normal limits. Since uromodulin is synthetized exclusively within tubules, though it is not a disease-specific marker, it can point to a predominantly tubular injury. Further research is needed to explore the timely expression of uromodulin and miRNAs associated with transplant pathology patterns, in order to detect kidney allograft pathology on a subclinical level, tailor response to therapy, and predict graft outcome.

**Supplementary Materials:** Supplementary materials can be found at http://www.mdpi.com/1422-0067/21/16/ 5592/s1, Table S1: Association of selected miRNAs with kidney graft disorder and relevant gene target(s), Figure S1: Association of miRNAs (*miR-29c, miR-126, miR-146a, miR-150, miR-155, miR-223*) with kidney graft disease in patients with performed kidney graft biopsy due to indication after miRNA measurement.

**Author Contributions:** Conceptualization, Ž.V.-H., N.K.; methodology, Š.B., E.B., Ž.P.T., D.K.; software, Š.B., E.B., Ž.P.T.; formal analysis, Š.B., Ž.V.-H., E.B., Ž.P.T., J.L., D.K., N.K.; investigation, Š.B., Ž.V.-H., E.B., Ž.P.T., J.L., D.K., N.K.; data curation, Š.B., Ž.V.-H., E.B., Ž.P.T., J.L., D.K., N.K.; writing—original draft preparation, Š.B., E.B., Ž.P.T.; writing—review and editing, Ž.V.-H., N.K.; supervision, Ž.V.-H., N.K.; funding acquisition, Ž.V.-H., J.L., D.K., N.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research was partially funded by Slovenian ARRS program No P3-0323 and P3-0054.

**Acknowledgments:** The authors would like to thank all medical nurses from the Department of Nuclear Medicine and Center for Kidney Transplantation of the Department of Nephrology at the University Medical Center Ljubljana for their cooperation and care of our patients.

**Conflicts of Interest:** The authors declare no conflict of interest.
