Variation in Definitions of Kidney Abnormality in Patients with Spina Bifida: A Systematic Scoping Review.

PURPOSE: We systematically reviewed the variability in definitions of kidney abnormality (KA) outcomes in individuals with spina bifida (SB). MATERIALS AND METHODS: A systematic scoping review was conducted using MEDLINE, Embase™, Cochrane Library, CINAHL, PsycInfo®, Web of Science™ and ClinicalTrials.gov for articles from time of database inception to September 2020. No language or patient age restrictions were applied. Primary research articles involving individuals with SB where KA was assessed as an outcome were included. Means of assessing KA and defining KA severity were abstracted. RESULTS: Of 2,034 articles found, 274 were included in the review. Most articles were published after 1990 (63.5%) and included pediatric-only populations (0-18 years; 60.5%). KA outcomes were identified by imaging-based anatomical outcomes (84.7%), serum-based outcomes (44.9%), imaging-based functional outcomes (5.5%), urine-based outcomes (3.3%) and diagnoses of end-stage kidney disease (2.6%) or chronic kidney disease otherwise unspecified (1.8%). Hydronephrosis was the most commonly used specific outcome (64.6%, 177/274) with 19.8% (35/177) of articles defining hydronephrosis severity. Hydronephrosis was used more frequently in articles with pediatric-only populations. Creatinine and cystatin-C were used in 82.1% (101/123) and 17.9% (22/123) of articles reporting serum-based outcomes, respectively, with 32.7% and 50.0% of articles defining estimated glomerular filtration rate (GFR) severity. Serum-based outcomes were more common in articles including adults >18 years. Measured GFR was assessed in 9.9% (27/274) of articles, with 44.4% (12/27) of articles defining GFR severity. CONCLUSIONS: Significant variability exists in how authors define KA with few specifically defining KA severity. Consensus and consistency in defining KA outcomes are needed.

Variability in Kidney Function Estimates in Emerging Adults With Spina Bifida: Implications for Transitioning From Pediatric to Adult Care.

OBJECTIVE: To examine the variability of estimated glomerular filtration rate (eGFR) in emerging adults with spina bifida (SB) by comparing multiple equations across the transitional age period, hypothesizing that creatinine (Cr)-based equations show greater variability than cystatin-C (CysC)- or combination-based equations. METHODS: A retrospective cohort study was performed from 2012 to 2017 at a multidisciplinary SB clinic. Emerging adults were defined as patients ages 18-28 years old. Four pediatric, 3 adult, and 3 averaged eGFR equations were considered. Cross-sectional variability in eGFR data was assessed using coefficients of variation, chronic kidney disease (CKD) stage classification, and pairwise percent relative difference in eGFR between analogous pediatric and adult equations based on included lab values. Longitudinal changes in eGFR over time were compared across equations using a covariance pattern model accounting for repeated measures. RESULTS: Seventy-five emerging adults with SB (median age 21.8 years; 55% female; 83% with myelomeningocele) were included in cross-sectional analyses. Adult equations gave higher median eGFRs by 22%-27% and generally milder CKD stage classification than analogous pediatric equations. In longitudinal analyses (median follow-up of 22 months), all equations conferred negative eGFR changes over time (range -1.9 to -4.3 mL/min/1.73m2 per year) that were not significantly different. CONCLUSION: In emerging adults with SB, adult equations demonstrated higher median eGFRs by 22%-27% compared to analogous pediatric equations, even with Cystatin-C, and generally downstaged CKD stage classification. The same eGFR equation should be used for serial kidney function monitoring in emerging adults with SB who transition care from pediatric to adult services.

Diagnostic Test Characteristics of Ultrasound Based Hydronephrosis in Identifying Low Kidney Function in Young Patients with Spina Bifida: A Retrospective Cohort Study.

PURPOSE: Kidney dysfunction in spina bifida is usually detected by low estimated glomerular filtration rate or ultrasound based hydronephrosis. We assessed the diagnostic test characteristics of hydronephrosis for detecting low estimated glomerular filtration rate, hypothesizing that hydronephrosis has low sensitivity compared to cystatin C based estimated glomerular filtration rate. MATERIALS AND METHODS: We conducted a single center, retrospective cohort study, including patients with spina bifida from 2012-2017 with 2 kidneys and complete data needed to calculate estimated glomerular filtration rate via multiple pediatric (age 1-17.9 years) or adult (age ≥18 years) estimating equations. We evaluated the association of hydronephrosis status (high grade, low grade or none) with estimated glomerular filtration rate, adjusting for small kidney size and scarring, and calculated diagnostic test characteristics of hydronephrosis for low estimated glomerular filtration rate. RESULTS: We analyzed 247 patients (176 children and 71 adults). Mean±SD age was 13.7±6.6 years, and 81% of patients had myelomeningocele. Hydronephrosis (77% low grade) was found in 35/176 children and 18/71 adults. Hydronephrosis was associated with low estimated glomerular filtration rate in stepwise fashion, independent of kidney size and scarring. However, across cystatin C based pediatric equations, any hydronephrosis (compared to none) had 23%-48% sensitivity, and high grade hydronephrosis (compared to none or low grade) had 4%-15% sensitivity for estimated glomerular filtration rate <90 ml/min/1.73 m2, which remained unchanged after excluding small kidneys and scarring. Across cystatin C based adult equations, any and high grade hydronephrosis had 55%-75% and 40%-100% sensitivity, respectively, for estimated glomerular filtration rate <90 ml/min/1.73 m2, although with wide confidence intervals. Specificity was higher with high grade vs any hydronephrosis. Sensitivities were higher for estimated glomerular filtration rate <60 ml/min/1.73 m2. CONCLUSIONS: Hydronephrosis was associated with low estimated glomerular filtration rate but had poor sensitivity for cystatin C based estimated glomerular filtration rate <90 ml/min/1.73 m2, especially among children with spina bifida.

Estimated kidney function in children and young adults with spina bifida: A retrospective cohort study.

AIMS: Current estimated glomerular filtration rate (eGFR) equations may be inaccurate in patients with spina bifida (SB) because of reduced muscle mass and stature. Cross-sectional and longitudinal variability of eGFR were analyzed in these patients across multiple equations, hypothesizing greater variability in creatinine-based than cystatin-C (Cys-C)-based equations. METHODS: This retrospective cohort study included children (age, 1-17.9 years) and adults (≥18 years) with SB from 2002-2017 at a large SB clinic. Those without all data needed to calculate eGFR were excluded. Four pediatric and three adult eGFR equations were compared for cross-sectional outcomes of eGFR and elevated office blood pressures using chronic kidney disease (CKD) stage classification, and for longitudinal outcome of eGFR slope over time using covariance pattern models accounting for repeated measures. RESULTS: One hundred and eighty two children and 75 adults had greater than or equal to 1 set of data measurements; 118 and 52, respectively, had greater than or equal to 2 sets. The pediatric bedside Schwartz equation had the highest median eGFR and coefficient of variation. CKD stage classification by eGFR showed large differences across equations in children, with rates of eGFR < 60 and <90 ml/min/1.73 m2 ranging from 2%-9% and 5%-69%, respectively. Only one equation showed a significant inverse association between eGFR and blood pressure. Longitudinally, eGFR slopes over time were different across pediatric equations (P < .001) but not adult equations. The bedside Schwartz equation had a positive eGFR slope; the other Cys-C-containing equations had negative slopes. CONCLUSIONS: Creatinine-based equations in children with SB vary considerably from cystatin-C-containing equations in calculating both single point-in-time eGFR values and eGFR trends over time.

Clinical grand rounds: atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (aHUS) is a rare, lifethreatening, chronic, genetic disease of uncontrolled alternative pathway complement activation. The understanding of the pathophysiology and genetics of this disease has expanded over recent decades and promising new developments in the management of aHUS have emerged. Regardless of the cause of aHUS, with or without a demonstrated mutation or autoantibody, blockade of terminal complement activation through C5 is of high interest as a mechanism to ameliorate the disease. Eculizumab, an existing monoclonal antibody directed against C5 with high affinity, prevents the perpetuation of the downstream activation of the complement cascade and the damage caused by generation of the anaphylotoxin C5a and the membrane attack complex C5b-9, by blocking C5 cleavage. We report the successful use of eculizumab in a patient after kidney transplantation and discuss the disease aHUS.

Tubulointerstitial injury and the progression of chronic kidney disease.

In chronic kidney disease (CKD), once injury from any number of disease processes reaches a threshold, there follows an apparently irreversible course toward decline in kidney function. The tubulointerstitium may play a key role in this common progression pathway. Direct injury, high metabolic demands, or stimuli from various other forms of renal dysfunction activate tubular cells. These, in turn, interact with interstitial tissue elements and inflammatory cells, causing further pathologic changes in the renal parenchyma. The tissue response to these changes thus generates a feed-forward loop of kidney injury and progressive loss of function. This article reviews the mechanisms of this negative cycle mediating CKD.