Congenital Solitary Functioning Kidney: A Review

Background: Solitary functioning kidney (SFK) is a subgroup of the Congenital Anomalies of the Kidneys and Urinary Tract (CAKUT). Although the prognosis of these patients was considered good in the past, numerous studies have shown different levels of kidney damage associated with this condition. Serum creatinine measurement is still the most used marker to assess renal function, even though the limitations are widely known. Objective: The present review aims to summarize and update the scientific literature on congenital SFK, discussing its pathophysiology, diagnosis, complications, prognosis, role of novel urinary biomarkers, treatment, and follow-up. Results: The natural history of congenital SFK is still an unresolved issue due to several factors. Although it has not yet been proven in humans, Brenner’s hyperfiltration hypothesis is the most concrete theory to explain the poor renal outcomes of patients born with one functioning kidney. The search for novel urinary biomarkers capable of assessing renal function and predicting renal outcomes has already started, but there are still few studies on this specific population. Among the most studied markers, Cystatin C, EGF and NGAL have shown potential usefulness for the follow-up of these patients. The treatment still relies on the search for kidney injury and general renoprotective measures. Conclusion: Further research with a longer follow-up duration is needed to better understand the natural course of congenital SFK and the role of novel urinary biomarkers in this specific population. Thus, it will be possible to improve the prognosis of these patients.