Early Renal Ultrasound in Patients with Congenital Solitary Kidney Can Guide Follow-Up Strategy Reducing Costs While Keeping Long-Term Prognostic Information

Abstract

We aimed to evaluate the prognostic value of renal length (RL) > 2 standard deviation scores (SDS) measured by renal ultrasound (RUS), across infancy, childhood and adolescence, in identifying which patients with congenital solitary functioning kidney (CSFK) are at lower risk of developing kidney injury (KI). We also estimated the cost saving of integrating the current follow-up protocols with an early RUS algorithm (ERUSA). Fifty-six CSFK adult patients who were 1–3 months old at first observation of undergoing RUS were enrolled. KI was defined by hypertension and/or proteinuria and/or declined renal function. ERUSA was assessed by early (at 1–3 months of life) RUS and was retrospectively tested in our patients. ERUSA establishes that patients with RL > 2SDS at early RUS do not undergo further follow-ups. The others undergo another RUS at 1 year of age along with follow-ups according with current protocols, with the exception of RUS which could be no longer performed. Direct and indirect costs were calculated for each analysed protocol and the cost saving of applying ERUSA was calculated. None of the patients with early RL > 2SDS presented KI in adulthood. A RL > 2SDS was predictive of absence of KI only at 1–3 months (OR = infinity) and 1 year of age (OR = 0.13; 95%CI: 0.03–0.66; p = 0.01). ERUSA provided a total cost-sparing ranging from 38.6% to 55.3% among the analysed follow-up protocols. With ERUSA, no patients developing KI in adulthood were missed. In conclusion, only a RL > 2SDS at 1–3 months and 1 year of age predicted good prognosis in young adulthood. ERUSA can guide a cost-sparing follow-up strategy in CSFK patients while maintaining important long-term information.

The importance of a correct timing of kidney ultrasound in patients with congenital solitary kidney

“…To reinforce the utility of KUS in CSFK, we want to emphasize that a precise timing of KUS in CSFK could be useful to select patients with lower risk of presenting VUR 2 or kidney injury (defined as persistent reduced estimated glomerular filtration rate [eGFR] and/or proteinuria and/or hypertension). 3,4 In fact, a KUS-measured kidney length (KL) > 2 standard deviation scores (SDS) in the first month of life could indicate an increased nephron endowment (renal hyperplasia) as result of prenatal compensatory nephron formation with subsequent reduced risk of kidney injury. 3,4 Moreover, the prevalence of VUR is significantly lower among CSFK patients presenting with KL > 2 SDS within 3 months of life and the KL > 2 SDS predicts absence of VUR.…”

“…3,4 In fact, a KUS-measured kidney length (KL) > 2 standard deviation scores (SDS) in the first month of life could indicate an increased nephron endowment (renal hyperplasia) as result of prenatal compensatory nephron formation with subsequent reduced risk of kidney injury. 3,4 Moreover, the prevalence of VUR is significantly lower among CSFK patients presenting with KL > 2 SDS within 3 months of life and the KL > 2 SDS predicts absence of VUR. 2 This founds its explanation in the fact that a longer KL is less likely to indicate dysplasia from in utero VUR.…”

“…Increasing the age, the rate of CSFK patients attaining a KL > 2 SDS increases up to 85.7% in adulthood. 4 The period of life in which CSFK patients reach a KL > 2 SDS can be expression of their nephron endowment. If a KL > 2 SDS is prenatally reached, it implies an increased nephron formation with subsequent better outcomes compared with patients reaching a KL > 2 SDS later in life, which, in turn, present better outcomes compared with patients never attaining KL > 2 SDS.…”

“…If a KL > 2 SDS is prenatally reached, it implies an increased nephron formation with subsequent better outcomes compared with patients reaching a KL > 2 SDS later in life, which, in turn, present better outcomes compared with patients never attaining KL > 2 SDS. 4 Recently, to reduce unnecessary procedures and economic costs in CSFK patients, the application of the early renal ultrasound algorithm (ERUSA) has been suggested. 4 ERUSA establishes that-in absence of complex features-CSFK patients with KL > 2 SDS at early KUS (between 1 and 3 months of life) do not undergo further KUSs, while the other patients undergo another KUS at 1 year of age without further following KUSs.…”

“…4 Recently, to reduce unnecessary procedures and economic costs in CSFK patients, the application of the early renal ultrasound algorithm (ERUSA) has been suggested. 4 ERUSA establishes that-in absence of complex features-CSFK patients with KL > 2 SDS at early KUS (between 1 and 3 months of life) do not undergo further KUSs, while the other patients undergo another KUS at 1 year of age without further following KUSs. 4 This because none of the patients born with KL > 2 SDS presented kidney injury during follow-up until adulthood and a KL > 2 SDS was predictive of absence of later kidney injury only until 1 years of age.…”