Article of the Month - Dec 2019

Survival and Kidney Outcomes of Children with an Early Diagnosis of Posterior Urethral Valves

CLASN, Vol 14, November, 2019; doi: 10.2215/CJN.04350419

Herbst KW, Tomlinson P, Lockwood G, Mosha MH, D’Alessandri-Silva C

Reviewed by Alison Kent

Background

Posterior urethral valve (PUV) is an important cause of chronic kidney disease in boys, with an estimated 15-20% of patients with PUV progressing to end-stage kidney disease (ESKD). Progression to ESKD may occur in early as infancy in some or in late childhood in others. Our ability to provide prognostic information to parents in the immediate post-natal period is limited. Epidemiologic data such as what is found in this study aids in our understanding of the natural history of PUV.

What was the purpose of the study?

The authors aimed to describe the rate and timing of kidney-related outcomes for children diagnosed early in life with posterior urethral valves in the USA, using the Pediatric Health Information System database.

What was the study design?

Retrospective review of data in the Pediatric Health Information System – contains data from over 52 not-for-profit tertiary care pediatric hospitals in the USA. Includes inpatient, emergenc department, ambulatory surgery and encounter-level data.

What were the characteristics of the sample?

Children with an inpatient hospitalization between January1 to December 31 2006 during 1st year of life with an ICD-9 code of congenital urethral stenosis who either died or had an ICD-9 procedure coded for valve ablation.

Exclusion criteria – patients diagnosed with bladder exstrophy, prune belly syndrome, neurogenic bladder or spinal dysraphism

Data on initial hospitalisation were abstracted including demographics, comorbidities, dates of intervention and disposition. Children then followed until December 31 2018 for kidney-related mortality, placement of a dialysis catheter or kidney transplant.

What are the results/main learning points?

685 children were included from 38 hospitals – 45% were Caucasian. The median age at initial hospitalization was 7 days [IQR 1-37 days]. Over 90% had an initial hospitalization length of stay of 30 days or less [IQR 4-14 days]. One third of participants did not have a subsequent hospitalization. Of those with subsequent visits median follow-up was 7 years.

5% of children died during the study period – over half during their initial hospitalization and 85% within the first 2 years. Greatest risk factor for mortality was pulmonary hypoplasia followed by prematurity. Patients who were cared for in a unit that looked after more than 3 cases per year were 62% less likely to die.

9% underwent one or more procedures for catheter placement for dialysis. 56% of these occurred in the initial hospitalization. Median age for the remaining catheter placements was 33 months. 44% of those with catheter placement progressed to kidney transplant. Highest risks for catheter placement were diagnosis of dysplastic kidney, pulmonary hypoplasia and prematurity.

7% underwent kidney transplant (excluding patients whose initial hospitalization was in a hospital without a transplant program) with median age of 38 months. Only one during first year of life with over 50% occurring before 5 years of age. Greatest risk factor for transplant was dysplastic kidney.

Survival for posterior urethral valves 98% in first month of life, 95% at 1 year of life and minimal change from 5 to 10  and 15 years of life. Pulmonary hypoplasia greater reduced probability of survival.

Mean ESKD intervention-free time was 19 years. Probability of catheter placement at 1 year of age 7% and at 15 years 20%.

What are the implications?

While this study does not take into account terminations of pregnancy or fetal death in-utero, if able to survive the early neonatal period due to pulmonary hypoplasia the long-term survival for children with posterior urethral valves is very positive with less than 10% requiring dialysis catheter placement or renal transplant. Ongoing need for markers of poor kidney outcomes.