**4. Results**

None of the patients presented with eGFR < 60 mL/min/1.73 m<sup>2</sup> and median eGFR values in both groups were above 90 mL/min/1.73 m<sup>2</sup> at any time point (Table 1) Most oncological patients demonstrated hyperfiltration until the 3rd week after transplantation (with peak incidence in the first week after HSCT). Non-oncological children with eGFR > 140 mL/min/1.73 m<sup>2</sup> were in minority. The median eGFR values in non-oncological children were comparable to those of the controls during the whole study except for the early (24 h after HSCT) measurement, when they became significantly higher (Table 1). Contrarily, the eGFR records in oncological patients remained significantly elevated compared to controls from point zero until the 3rd week after alloHSCT. They were increased throughout the whole study period compared to the non-oncological patients (Table 1).


**Table 1.** eGFR values in examined groups.

*p* < 0.05 oncological pts vs. non-oncological pts; *p* < 0.05 any time point vs. before alloHSCT; *p* < 0.05 2 weeks after vs. 3 weeks after; eGFR estimated glomerular filtration rate; alloHSCT allogeneic hematopoietic stem cell transplantation.

The urinary clusterin, KIM-1 and cystatin C concentrations were significantly elevated in all patients compared to controls, irrespective of the indication for transplantation (oncological or non-oncological), even before alloHSCT. Normalization of the urinary concentrations of clusterin, KIM-1 and cystatin C for urinary creatinine maintained these di fferences (Figures 2–4). In the case of clusterin, the urinary values have increased nearly 3-fold 24 h after transplantation, then kept the plateau phase until the second week and rose again in the 3rd week. Finally, they decreased in the 4th week after HSCT, ye<sup>t</sup> remained higher than before HSCT (Figure 2). The urinary KIM-1 values rose by 50% 24 h after HSCT, then kept growing until the 3rd week and finally decreased (Figure 3). Urinary cystatin C demonstrated the delayed elevation from the 2nd week after transplantation, lasting only until the 3rd week and followed by a significant decrease 1 week later (Figure 4). After 4 weeks of observation, all urinary biomarkers were still significantly elevated compared to the pre-transplantation values.

**Figure 2.** Urinary clusterin values in examined groups. before—before alloHSCT; after—24 h after alloHSCT; 1 w (2 w, 3 w, 4 w)—1 week (2, 3, 4 weeks) after alloHSCT.

**Figure 3.** Urinary KIM-1 values in examined groups. before—before alloHSCT; after—24 h after alloHSCT; 1 w (2 w, 3 w, 4 w)—1 week (2, 3, 4 weeks) after alloHSCT.

**Figure 4.** Urinary cystatin C values in examined groups. before—before alloHSCT; after—24 h after alloHSCT; 1 w (2 w, 3 w, 4 w)—1 week (2, 3, 4 weeks) after alloHSCT.

The serum concentrations of clusterin, KIM-1 and cystatin C in children before transplantation were significantly higher than in controls (Table 2). The serum values further increased 24 h after HSCT and the rise was most spectacular in the case of clusterin (over 2-fold) compared to 50%–60% elevation of other markers. Then the concentrations rose systematically until the 3rd week (clusterin) or 4th week (KIM-1, cystatin C) after alloHSCT. There was no significant difference in the urinary or serum marker values between oncological and non-oncological patients at any time point (Table 2).



a *p* < 0.05 any time point vs. control group; b *p* < 0.05 24 h after alloHSCT vs. before alloHSCT; c *p* < 0.05 1 week after alloHSCT vs. 24 h after alloHSCT; d *p* < 0.05 2 weeks after alloHSCT vs. 1 week after alloHSCT; e *p* < 0.05 3 weeks after alloHSCT vs. 2 weeks after alloHSCT; f *p* < 0.05 4 weeks after alloHSCT vs. 3 weeks after alloHSCT. No significant correlations were detected between the analyzed parameters.

AKI was diagnosed in 4 patients (3 oncological and 1 non-oncological), according to the pRIFLE criteria. Risk stage was diagnosed in 3 of them, 1 developed Injury stage. None of the patients required renal replacement therapy.
