Clinico-Biochemical Profile of Children with Congenital Anomalies of the Kidney and Urinary Tract: A Cross-Sectional Study

Validation of ICD-9-CM codes for major genitourinary birth defects in Military Health System administrative data, 2006-2014

BACKGROUND

The Department of Defense Birth and Infant Health Research program is dedicated to birth defects research and surveillance among military families. Here, we assess and refine the validity of International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes for selected genitourinary birth defects in the Military Health System (MHS). We additionally outline methods for the calculation of positive predictive value (PPV) and negative predictive value (NPV), sensitivity, and specificity using a stratified sampling design.

METHODS

Among military infants born from 2006 through 2014, a random sample of ICD-9-CM screen-positive cases (for six genitourinary birth defects) and screen-negative cases were selected for chart review. PPV, NPV, sensitivity, and specificity were calculated for individual defects and any included defect (i.e., overall); measures were weighted by the inverse probability of being sampled.

RESULTS

Of 461,557 infants, 686 were sampled for chart review. Bladder exstrophy was accurately reported (PPV: >90%), while the accuracy of renal dysplasia, renal agenesis/hypoplasia, and hypospadias was moderate (PPVs: 66%-68%) and congenital hydronephrosis was low (PPV: 20%). Specificity and NPVs always exceeded 98%. The overall PPV was 50%; however, excluding congenital hydronephrosis screen-positive cases and requiring at least two inpatient or outpatient diagnostic codes resulted in a PPV of 85%.

CONCLUSIONS

The validity of major genitourinary birth defect codes varied in MHS administrative data. The accuracy of an overall defect measure improved by omitting congenital hydronephrosis and requiring at least two diagnostic codes. Although PPV is generally useful for research, additional calculation of NPV, sensitivity, and specificity better informs the identification of appropriate selection criteria across surveillance and research settings.

Reference values for urinary protein, albumin, beta 2-microglobulin, and the alpha 1-microglobulin-to-creatinine ratio in Japanese children

BACKGROUND

The importance of the ratio of creatinine to urinary protein, albumin, and low-molecular weight protein as a urinary marker in chronic kidney disease patients is widely recognized. However, no reference values have hitherto been established for these markers in Japanese children. The present study aimed to establish the reference values for these urinary markers in Japanese children.

METHODS

The first morning urine was randomly collected from 1712 pupils aged ≥ 3 to < 18 years during school and kindergarten mass urinary screenings. The upper limit of the reference values was set at the 97.5th percentile of the creatinine ratio per marker.

RESULTS

The urinary protein-to-creatinine ratio (PCR), urinary albumin-to-creatinine ratio (ACR), urinary beta 2-microglobulin-to-creatinine ratio (BMCR), and urinary alpha 1-microglobulin-to-creatinine ratio (AMCR) showed an age-related decrease at the 50th percentile reflecting an age-related increase in urinary creatinine. The appropriate reference value for the PCR and ACR was 0.12 g/gCr and 35 mg/gCr, respectively, in the entire cohort. The appropriate reference value for the BMCR was 0.5 μg /mgCr for age ≥ 3 to < 6 years and 0.35 μg/mgCr for age 6 years or older. The appropriate reference value for the AMCR was 5.0 μg/mgCr for age ≥ 3 to < 6 years and 3.5 μg /mgCr for age 6 years or older.

CONCLUSION

The present study was the first to determine appropriate reference values for the PCR, ACR, BMCR, and AMCR based on an analysis of the first morning urine samples of a large number of children.

PAX2 Gene Mutation in Pediatric Renal Disorders-A Narrative Review

The PAX2 gene is a transcription factor that is essential for the development of the urinary system among other transcription factors. The role of PAX2 is highlighted from the seventh week of gestation, when it is involved in development processes and the emergence of nephrons and collecting tubes. Being an important factor in renal development, mutations of this gene can produce severe alterations in the development of the urinary tract, namely congenital anomalies of the kidneys and urinary tract. The first reported cases described with the PAX2 mutation included both renal anomalies and the involvement of other organs, such as the eyes, producing renal coloboma syndrome. Over the years, numerous cases have been reported, including those with only renal and urinary tract anomalies. The aim of this review is to present a summary of pediatric patients described to have mutations in the PAX2 gene to contribute to a better understanding of the genetic mechanism causing anomalies of the kidneys and urinary tract. In this review, we have included only pediatric cases with renal and urinary tract disorders, without the involvement of other organs. From what we know so far from the literature, this is the first review gathering pediatric patients presenting the PAX2 mutation who have been diagnosed exclusively with renal and urinary tract disorders.

β2-microglobulin measurement with dried urine spots for congenital anomalies of the kidney and urinary tract screening in 3-year-old children

BACKGROUND

Screening using dipstick urinalysis has long been performed in 3-year-old children; however, it is ineffective in detecting congenital anomalies of the kidney and urinary tract (CAKUT). Measurement of the urinary β2-microglobulin (β2MG)/creatinine (Cr) ratio may be more effective for this purpose. Analysis of dried urine spots (DUS) on filter paper is suitable for mass screening since operational costs are low and samples are easy to collect and transport. We examined the accuracy of measuring the urinary β2MG/Cr ratio in DUS on filter paper.

METHODS

We collected 2,623 urine samples from 3-year-old children. β2MG and Cr levels were measured in DUS on filter paper. We examined the correlation between the β2MG/Cr ratios measured in DUS and using the conventional method in 640 samples using the coefficient of determination test. Children with high β2MG/Cr ratios (>0.6 µg/mg Cr) in DUS samples were further examined to establish a definitive diagnosis.

RESULTS

There was strong correlation between the two methods for determination of β2MG levels (r²  = 0.68; P < 0.001) and β2MG/Cr ratios (r²  = 0.69; P < 0.001). Of the 2,623 children, 38 (1.45%) had β2MG/Cr ratios >0.6. Thirty-five children were subsequently examined, resulting in findings of renal hypodysplasia (n = 2, 0.08%), horseshoe kidney (n = 1, 0.04%), renal tubular dysfunction with hepatoblastoma (n = 1, 0.04%), data abnormality (high urine β2MG level, n = 6, 0.23%; high serum Cr level, n = 1, 0.04%), and normal values (n = 24, 0.91%).

CONCLUSIONS

We evaluated a practical method for measuring β2MG/Cr ratios in DUS as a screening method to detect CAKUT in 3-year-old children.

Arterial hypertension and cystatin C during neonatal physiologic dehydration

A reduced nephron number may play a role in the pathogenesis of arterial hypertension (AH), and it is well recognized that individual nephron endowment is widely variable. However, nephrons count is technically impossible in vivo. Based on the observation that subjects with a reduced nephron mass exhibit an increase in renal functional biomarkers during acute dehydration, we hypothesized that cystatin C concentration during neonatal physiological dehydration could identify subjects with reduced nephron endowment. This is a prospective, observational, cohort study enrolling healthy, caucasian, term neonates born after an uneventful pregnancy. Two groups of newborns were compared: neonates born to fathers on antihypertensive treatment (HF) versus those born to proven normotensive fathers older than 40 years of age (NF). Enrolled newborns underwent cystatin C determination at the time of newborn screening. Forty newborns with HF and 80 with NF were enrolled. No differences in baseline characteristics were observed between the two groups except for the number of hypertensive grandparents higher among newborns to HF (47.8% vs. 21.1%; p: 0.001). Cystatin C was significantly higher in newborns with HF (1.62 ± 0.30 mg/L vs 1.41 ± 0.27 mg/L; p < 0.001). Linear regression analysis corrected for confounders confirmed that paternal hypertension was the only variable significantly associated with high cystatin C level during post-natal dehydration. Besides offering new insights on the pathogenesis of familial hypertension, our results support the specific role of nephron endowment and suggest the possibility of identifying subjects at risk for reduced nephron endowment as early as at birth.