**3. Results**

The characteristics of the study group are shown in Table 1.


**Table 1.** Characteristics of the study group.

ACEI—angiotensin-converting enzyme inhibitor; ARB—angiotensin receptor blocker; FU—end of follow-up; *n*—number of patients.

The mean age at the diagnosis of IgAN was 11 ± 4.29 years. Boys and girls comprised 61.47% and 38.53% of the study group, respectively. A kidney biopsy was performed on average 1.2 ± 1.77 years since the initial symptoms, and the mean duration of follow-up was 45 ± 30.75 months.

At baseline, the mean proteinuria was 44.57 ± 120.04 mg/kg/d, creatinine level was 0.73 ± 0.33 mg/dL, and GFR was 96.75 ± 33.56 mL/min/1.73 m2. At the end of follow-up, the mean proteinuria was 10.11 ± 35.84 mg/kg/d, creatinine level was 0.71 ± 0.22 mg/dL and GFR was 100.65 ± 22.86 mL/min/1.73 m2.

At baseline, an elevated IgA level was noted in 73 patients (49.32%), and reduced C3 and C4 levels in 13 (8.78%) and 17 patients (11.49%), respectively. At the end of follow-up, an elevated IgA level was noted in 47 patients (31.76%), reduced C3 level in 12 (8.10%) and reduced C4 level in 26 patients (17.57%).

GFR was <90 mL/min in 58 (39.19%) children at baseline and in 46 (31.08%) children at the end of follow-up.

Regarding to the evaluation by the Oxford classification, mesangial hypercellularity (M1) was present in 81.76% of patients in the study group, endocapillary hypercellularity (E1) in 23.65%, segmental sclerosis (S1) in 28.39%, interstitial fibrosis/tubular atrophy (T1/2) in 18.24% and cellular/fibrocellular crescents (C1/2) in 27.7%.

The study group was categorized based on the presence of C3 deposits in kidney biopsy specimens. Low severity of C3 deposits was defined as C3 ≤ +1, and high severity as C3 > +1. Depending on the presence of C3 deposits in kidney biopsy specimens, the patients were divided into two groups: group A—C3 ≤ 1, group B—C3 > 1. The duration of follow-up was 4.19 ± 3.05 years in group A, and 2.91 ± 2.46 years in group B.

The clinical characteristics of the study patients divided into two groups based on the severity of C3 deposits are shown in Table 2.

**Table 2.** Clinical characteristics of the patient groups based on the severity of C3 deposits.


ACEI—angiotensin-converting enzyme inhibitor; ARB—angiotensin receptor blocker; FU—end of follow-up; *n*—number of patients.

No differences between group A (*n* = 98) and group B (*n* = 50) were found regarding to proteinuria and GFR at baseline and the end of follow-up. Serum creatinine level and severity of IgA and C3 deposits in kidney biopsy were significantly higher in group B (*p* < 0.01).

There were no significant differences between the two groups regarding to the overall MEST-C score.

Renoprotective treatment was used in 58 (59.2%) patients in group A and 21 (42.0%) patients in group B. Glucocorticosteroids were used in 13 (13.3%) patients in group A and 11 (22.0%) patients in group B. Immunosuppressive therapy was administered in 27 (27.6%) patients in group A and 17 (34.0%) patients in group B. Regarding to the drug treatment used, there was a significant difference only in renoprotective treatment

between the two groups, there were no significant differences in glucocorticosteroids and immunosuppressive therapy.

There was no difference in the mean GFR at the end of follow-up between patients in groups A and B, as well the percentages of patients with GFR >90 and <90 mL/min (*p* = 0.08).

Survival curve analysis using the Cox proportional hazard model showed a shorter duration of renal survival with normal GFR in children in group B (C3 >1 in kidney biopsy) compared to group A (C3 ≤ 1) (Figure 2). In the survival curve analysis, factors affecting longer renal survival with normal GFR included female gender (F > M, Figure 3), older age at the diagnosis and normal GFR at the onset of the disease (Figure 4).

The study group was also divided regarding to the MEST-C score (group I—MEST-C score ≤ 1, group II—MEST-C score > 1). The clinical characteristics of patients in these two groups are shown in Table 3. There were no significant differences between groups I and II regarding to albumin, C3 and C4 levels at baseline and the end of follow-up, and the severity of IgA, IgG and IgM deposits in kidney biopsy. Serum creatinine level at baseline was significantly higher in group II (*p* < 0.001), as was IgA level (*p* < 0.01). A significant difference was also found in GFR at baseline (group I > II; *p* < 0.01). At the end of follow-up, a significant difference was noted only for proteinuria which was higher in group II (*p* < 0.05).


**Table 3.** Clinical characteristics of the patient groups based on the MEST-C score.

FU—end of follow-up.

The study group was also divided based on serum C3 level (Group 1—serum C3 level below the reference range, Group 2—serum C3 level within the reference range). The clinical characteristics of patients in these two groups are shown in Table 4. No significant differences between Groups 1 and 2 were found regarding to the severity of proteinuria, GFR and creatinine, albumin and IgA levels at baseline and at the end of follow-up, as well as the intensity of IgA deposits in renal biopsy. Serum C4 level at baseline was significantly higher in Group 2 (*p* = 0.01) but no significant difference in C4 level was found between the groups at the end of follow-up.


**Table 4.** Clinical characteristics of the patient groups based on serum C3 level.

FU—end of follow-up.

**Figure 2.** Shorter renal survival with normal GFR in Group B (intensity of C3 deposits = +2, +3, +4) vs. Group A (intensity of C3 deposits = 0, +1).

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**Figure 4.** Shorter renal survival with normal GFR in patients with reduced GFR (<90 mL/min) at the time of the diagnosis.

Survival curve analysis using the Cox proportional hazard model showed no difference in renal survival with normal GFR between groups with normal and reduced serum C3 levels at baseline.
