Is the urinary biomarkers assessment a non-invasive approach to tubular lesions of the solitary kidney?

Introduction: The solitary kidney (SK) is currently debated in the literature, as living kidney donation is extensively used and the diagnosis of congenital SK is frequent. Tubulointerstitial lesions associated with adaptive phenomena may occur early within the SK.
Aims: Analysis of the significance of urinary biomarkers in the assessment of tubulointerstitial lesions of the SK.
Methods: A cross-sectional study of 37 patients with SK included 18 patients-acquired SK (mean age 56.44 ± 12.20 years, interval from nephrectomy 10.94 ± 9.37 years), 19 patients-congenital SK (mean age 41.52 ± 10.54 years). Urinary NAG, urinary alpha-1-microglobulin, albuminuria, eGFR (CKD-EPI equation) were measured.
Results: In acquired SK, NAG increased in 60.66%, urinary alpha 1-microglobulin in 16.66%, albuminuria in 55.55% of patients. Inverse correlation with eGFR presented NAG (R(2 )= 0.537, p = 0.022), urinary alpha 1-microglobulin (R(2 )= 0.702, p = 0.001), albuminuria (R(2 )= 0.655, p = 0.003). In congenital SK, NAG increased in 52.63%, urinary alpha 1-microglobulin in 5.26%, albuminuria in 47.36% of patients. In this group, urinary biomarkers correlated inversely with eGFR: NAG (R(2 )= 0.743, p < 0.001), urinary alpha 1-microglobulin (R(2 )= 0.701, p = 0.001), albuminuria (R(2 )= 0.821, p < 0.001). Significant correlations were found between the urinary biomarkers in both groups.
Conclusions: Urinary biomarkers allow a non-invasive, sensitive, early assessment of the tubular lesions of the SK. Urinary biomarkers of PT injury parallel renal function decline, thus complementing the estimation of GFR. Monitoring of PT dysfunction is mandatory in patients with SK.