Renal function in very low birth weight infants: normal maturity reached during early childhood

When will the Glomerular Filtration Rate in Former Preterm Neonates Catch up with Their Term Peers?

AIMS

Whether and when glomerular filtration rate (GFR) in preterms catches up with term peers is unknown. This study aims to develop a GFR maturation model for (pre)term-born individuals from birth to 18 years of age. Secondarily, the function is applied to data of different renally excreted drugs.

METHODS

We combined published inulin clearance values and serum creatinine (Scr) concentrations in (pre)term born individuals throughout childhood. Inulin clearance was assumed to be equal to GFR, and Scr to reflect creatinine synthesis rate/GFR. We developed a GFR function consisting of GFRbirth (GFR at birth), and an Emax model dependent on PNA (with GFRmax, PNA50 (PNA at which half ofGFR max is reached) and Hill coefficient). The final GFR model was applied to predict gentamicin, tobramycin and vancomycin concentrations.

RESULT

In the GFR model, GFRbirth varied with birthweight linearly while in the PNA-based Emax equation, GA was the best covariate for PNA50, and current weight for GFRmax. The final model showed that for a child born at 26 weeks GA, absolute GFR is 18%, 63%, 80%, 92% and 96% of the GFR of a child born at 40 weeks GA at 1 month, 6 months, 1 year, 3 years and 12 years, respectively. PopPK models with the GFR maturation equations predicted concentrations of renally cleared antibiotics across (pre)term-born neonates until 18 years well.

CONCLUSIONS

GFR of preterm individuals catches up with term peers at around three years of age, implying reduced dosages of renally cleared drugs should be considered below this age.

The Urinary Concentration of Trefoil Factor 3 (TFF3) in the Term and Preterm Neonates

BACKGROUND

Distinguishing between a pathologic state and renal development is important in neonatology. Because the assessment of serum creatinine in neonates is not reliable, better biomarkers are needed. Trefoil factor 3 (TFF3) is proposed as a biomarker of kidney injury. The study aimed to assess its urinary concentration in healthy term and stable preterm neonates.

MATERIAL AND METHODS

The study included 80 term and 20 preterm neonates born in the Department of Perinatology of the University Clinical Hospital in Bialystok. Urine was obtained from the term neonates on the 1st day of life and from the preterm neonates on the 1st, 8th, 15th and 22nd day of life. The urinary concentration of TFF3 was determined using a commercially available immunoassay and was normalized for the urinary creatinine concentration (cr.).

RESULTS

The values of TFF3/cr. were higher in the preterm than in the term neonates (p < 0.05) (median (Q1-Q3): 1486.85 (614.92-3559.18) and 317.29 (68.07-671.40) ng/mg cr.). They did not differ in the subsequent days of the preterm neonates' lives. The ROC curve for TFF3/cr. in the preterm and term neonates showed AUC = 0.751 (cut-off value = 1684.25 ng/mg cr.).

CONCLUSIONS

Prematurity is associated with higher urinary excretion of TFF3. Male gender is associated with an increased urinary TFF3 excretion in term neonates.

Characterization of the pattern of expression of Gas1 in the kidney during postnatal development in the rat

Growth Arrest-Specific 1 (Gas1) is a pleiotropic protein with different functions, in the adult kidney Gas1 acts as an endogenous inhibitor of cell proliferation but it is also necessary for the maintenance and proliferation of Renal Progenitor Cells (RPC) during early development, thus it fulfills important functions in the adult kidney. However, it is not known whether or not Gas1 is expressed during postnatal development, a critical stage for renal maturation. For this reason, the main objective of this work was to characterize the expression pattern of Gas1 in the different regions of the kidney by immunofluorescence and Western blot analysis during the postnatal development of the rat. We found that Gas1 is present and has a differential expression pattern in the various regions of the nephron during postnatal development. We observed that the highest levels of expression of Gas1 occur in the adult, however, Gas1 is also expressed in RPC and interestingly, the expression of RPC markers such as the Neural cell adhesion molecule (NCAM) and Cluster of differentiation 24 (CD24) were found to have an inverse pattern of expression to Gas1 (decreases as the kidney matures) during postnatal renal maturation, this indicates a role for Gas1 in the regulation of renal cell proliferation at this stage of development.

Maturation of glomerular filtration rate in neonates and infants: an overview

Glomerular filtration rate (GFR) increases progressively throughout fetal life, matures rapidly after birth according to gestational and post-menstrual age, and reaches adult values by 1-year post-natal age. GFR is considered the best marker of kidney function, and in clinical practice, estimated GFR is useful to anticipate complications, establish prognosis, and facilitate treatment decisions. This review article summarizes the maturation of glomerular filtration and the factors and conditions that modulate and impair developing glomerular filtration, and discusses the techniques available to assess GFR in neonates and infants. We focused on simple, reliable, easily available, and cheap techniques to estimate GFR, which may provide valuable information on the renal aspects of the clinical care of this group of patients.

The Long-Term Effect of Preterm Birth on Renal Function: A Meta-Analysis

The preterm-born adult population is ever increasing following improved survival rates of premature births. We conducted a meta-analysis to investigate long-term effects of preterm birth on renal function in preterm-born survivors. We searched PubMed and EMBASE to identify studies that compared renal function in preterm-born survivors and full-term-born controls, published until 2 February 2019. A random effects model with standardized mean difference (SMD) was used for meta-analyses. Heterogeneity of the studies was evaluated using Higgin’s I² statistics. Risk of bias was assessed using the Newcastle–Ottawa quality assessment scale. Of a total of 24,388 articles screened, 27 articles were finally included. Compared to full-term-born controls, glomerular filtration rate and effective renal plasma flow were significantly decreased in preterm survivors (SMD −0.54, 95% confidence interval (CI), −0.85 to −0.22, p = 0.0008; SMD −0.39, 95% CI, −0.74 to −0.04, p = 0.03, respectively). Length and volume of the kidneys were significantly decreased in the preterm group compared to the full-term controls (SMD −0.73, 95% CI, −1.04 to −0.41, p < 0.001; SMD −0.82, 95% CI, −1.05 to −0.60, p < 0.001, respectively). However, serum levels of blood urea nitrogen, creatinine, and cystatin C showed no significant difference. The urine microalbumin to creatinine ratio was significantly increased in the preterm group. Both systolic and diastolic blood pressures were also significantly elevated in the preterm group, although the plasma renin level did not differ. This meta-analysis demonstrates that preterm-born survivors may be subject to decreased glomerular filtration, increased albuminuria, decreased kidney size and volume, and hypertension even though their laboratory results may not yet deteriorate.

Simplified Dosing Regimens for Gentamicin in Neonatal Sepsis

Background: The effectiveness of antibiotics for the treatment of severe bacterial infections in newborns in resource-limited settings has been determined by empirical evidence. However, such an approach does not warrant optimal exposure to antibiotic agents, which are known to show different disposition characteristics in this population. Here we evaluate the rationale for a simplified regimen of gentamicin taking into account the effect of body size and organ maturation on pharmacokinetics. The analysis is supported by efficacy data from a series of clinical trials in this population.

Methods: A previously published pharmacokinetic model was used to simulate gentamicin concentration vs. time profiles in a virtual cohort of neonates. Model predictive performance was assessed by supplementary external validation procedures using therapeutic drug monitoring data collected in neonates and young infants with or without sepsis. Subsequently, clinical trial simulations were performed to characterize the exposure to intra-muscular gentamicin after a q.d. regimen. The selection of a simplified regimen was based on peak and trough drug levels during the course of treatment.

Results: In contrast to current World Health Organization guidelines, which recommend gentamicin doses between 5 and 7.5 mg/kg, our analysis shows that gentamicin can be used as a fixed dose regimen according to three weight-bands: 10 mg for patients with body weight <2.5 kg, 16 mg for patients with body weight between 2.5 and 4 kg, and 30 mg for those with body weight >4 kg.

Conclusion: The choice of the dose of an antibiotic must be supported by a strong scientific rationale, taking into account the differences in drug disposition in the target patient population. Our analysis reveals that a simplified regimen is feasible and could be used in resource-limited settings for the treatment of sepsis in neonates and young infants with sepsis aged 0–59 days.

Birth weight and renal markers in children aged 5-10 years in Cameroon: a cross-sectional study

Background

A relationship exists between birth weight (BW) and glomerular filtration rate (GFR) in postnatal kidney. Willing to fill a gap of knowledge in sub-Saharan Africa, we assessed the effect of BW on blood pressure (BP), proteinuria and GFR among Cameroonians children.

Methods

This was a cross-sectional hospital-based study from January to April 2018 at the Yaounde Gynaeco-Obstetric and Paediatric Hospital (YGOPH). We recruited low BW (LBW) [< 2500 g], normal BW (NBW) [2500-3999 g] and high BW (HBW) [> 4000 g] children, aged 5–10 years, born and followed-up at YGOPH. We collected socio-demographic, clinical (weight, height, BP), laboratory (proteinuria, creatinine), maternal and birth data. The estimated GFR was calculated using the Schwartz equation.

Results

We included 80 children (61.2% boys) with 21 (26.2%) LBW, 45 (56.2%) NBW and 14 (15.5%) HBW; the median (interquartile range) age was 7.3 (6.3–8.1) years and 17 (21.2%) were overweight/obese. Two (2.5%) children, all with a NBW (4.4%), had an elevated BP whereas 2 (2.5%) other children, all with a LBW (9.5%), had hypertension (p = 0.233). Seven (8.7%) children had proteinuria with 19, 2.2 and 14.3% having LBW, NBW and HBW, respectively (p = 0.051). Equivalent figures were 18 (22.5%), 14.3, 24.2 and 28.6% for decreased GFR, respectively (p = 0.818). There was a trend towards an inverse relationship between BW and BP, proteinuria and GFR (p > 0.05).

Conclusion

Proteinuria is more pronounced in childhood with a history of LBW and HBW while LBW children are more prone to develop hypertension. Regular follow-up is needed to implement early nephroprotective measures among children with abnormal BW.

Birth Injury: Birth Asphyxia and Birth Trauma

Injury to a fetus or neonate during delivery can be due to several factors involving the fetus, placenta, mother, and/or instrumentation. Birth asphyxia results in hypoxia and ischemia, with global damage to organ systems. Birth trauma, that is mechanical trauma, can also cause asphyxia and/or morbidity and mortality based on the degree and anatomic location of the trauma. Some of these injuries resolve spontaneously with little or no consequence while others result in permanent damage and severe morbidity. Unfortunately, some birth injuries are fatal. To understand the range of birth injuries, one must know the risk factors, clinical presentations, pathology and pathophysiology, and postmortem autopsy findings. It is imperative for clinicians and pathologists to understand the causes of birth injury; recognize the radiographic, gross, and microscopic appearances of these injuries; differentiate them from inflicted postpartum trauma; and work to prevent future cases.

Urinary biomarkers in the early detection and follow-up of tubular injury in childhood urolithiasis

BACKGROUND

To investigate relationships among urinary biomarkers [kidney injury molecule-1 (KIM-1), N-acetyl-β-glucosaminidase (NAG)], neutrophil gelatinase-associated lipocalin (NGAL) levels and renal tubular injury in childhood urolithiasis.

METHODS

Seventy children [36 girls, mean age: 7.3 ± 5.0 years (0.5-18.2)] with urolithiasis/microlithiasis and 42 controls [18 girls, mean age: 8.5 ± 3.8 years (0.9-16.2)] were included in this multicenter, controlled, prospective cohort study. Patients were evaluated three times in 6-month intervals (0, 6 and 12th months). Anthropometric data, urinary symptoms, family history and diagnostic studies were recorded. Urine samples were analyzed for metabolic risk factors (urinary calcium, uric acid, oxalate, citrate, cystine, magnesium, and creatinine excretion), and the urinary KIM-1, NAG, and NGAL levels were measured.

RESULTS

Stones were mostly located in the upper urinary system (82.9%), and six patients (8.6%) had hydronephrosis. Thirty patients (42.9%) had several metabolic risk factors, and the most common metabolic risk factor was hypocitraturia (22.9%). Urinary KIM-1/Cr, NAG/Cr and NGAL/Cr ratios were not significantly different between patients and controls. Furthermore, no significant changes in their excretion were shown during follow-up. Notably, the urinary KIM-1/Cr, NAG/Cr, and NGAL/Cr levels were significantly higher in children under 2 years of age (p = 0.011, p = 0.006, and 0.015, respectively). NAG/Cr and NGAL/Cr ratios were significantly increased in patients with hydronephrosis (n = 6, p = 0.031 and 0.023, respectively).

CONCLUSIONS

The results of this study suggest that none of the aforementioned urinary biomarkers (KIM-1, NAG and NGAL levels) may be useful for the early detection and/or follow-up of renal tubular injury and/or dysfunction in childhood urolithiasis.

Increased urinary neutrophil gelatinase-associated lipocalin in very-low-birth-weight infants with oliguria and normal serum creatinine

BACKGROUND

In infants, oliguria is defined as a urine output of <1.5 mL/kg/h. The aim of our study was to assess the impact of oliguria on urinary neutrophil gelatinase-associated lipocalin (NGAL) and serum cystatin C (CysC) levels in very-low-birth-weight infants (VLBWIs) with a normal serum creatinine (Cr) level.

METHODS

Fifty-seven VLBWIs were enrolled in the study. Urinary NGAL, serum CysC and Cr levels and urinary NGAL/Cr ratios were measured. Infants with Apgar scores of >5 at 5 min and/or a serum Cr level of >1.5 mg/dL or those treated for patent ductus arteriosus were excluded. In case of antibiotic treatment, blood and urine samples were collected at ≥48 h after discontinuation of antibiotic treatment.

RESULTS

There was a significant difference in gestational age between infants with oliguric episodes during hospitalization and those without, but not in birth weight, perinatal or postnatal factors. Gestational age was negatively correlated with urinary NGAL and serum CysC levels and urinary NGAL/Cr ratio (p < 0.05), whereas postnatal age was negatively correlated with serum Cr level and urinary NGAL/Cr ratio (p < 0.05). Of the 117 urine and blood samples collected, 25 (21.4%) were obtained from neonates with oliguric episodes. After adjusting for gestational age and postnatal age, comparison of samples collected in infants with and without oliguric episodes revealed significant differences in the mean level of urinary NGAL and in the urinary NGAL/Cr ratio, but not in mean serum CysC or serum Cr levels. The urinary NGAL level [area under the curve (AUC) 0.886, 95% confidence interval (CI) 0.814-0.937] and urinary NGAL/Cr ratio (AUC 0.853, 95% CI 0.775-0.911) showed significantly greater discrimination for oliguria than serum CysC (AUC 0.610, 95% CI: 0.515-0.699) or serum Cr (AUC 0.747, 95%CI 0.659-0.823) levels.

CONCLUSIONS

Urinary NGAL level and urinary NGAL/Cr ratio were more sensitive markers for the presence of oliguria in VLBWIs with normal serum Cr levels than serum CysC level.

Water Balance and 'Salt Wasting' in the First Year of Life: The Role of Aldosterone-Signaling Defects

In newborns and infants, dehydration and salt wasting represent a relatively common cause of admission to hospital and may result in life-threatening complications. Kidneys are responsible for electrolyte homoeostasis, but neonatal kidneys show low glomerular filtration rate and immaturity of the distal nephron, leading to reduced ability to concentrate urine. High extrarenal fluid losses often contribute to the increased occurrence of electrolyte disorders. Aldosterone is essential for sodium retention in the kidney, salivary glands, sweat glands and colon. A partial and transient aldosterone resistance is present in newborns and infants, thus reducing the capability of maintaining sodium balance in specific pathological conditions. The present review examines the mechanisms making infants more susceptible to salt wasting. Peculiar aspects of renal physiology in the first year of life and management of electrolyte disorders (i.e. sodium and potassium) are considered. Finally, inherited disorders associated with neonatal salt wasting are examined in detail. © 2016 S. Karger AG, Basel.

Effect of birth weight on adulthood renal function: A bias-adjusted meta-analytic approach

While the association between low birth weight (LBW; <2500 g) and development of adult chronic renal disease (CKD) is inconsistently reported, less information is available regarding association of high birth weight (HBW; ≥4000 g) with CKD. We undertook a systematic review and meta-analysis on studies published before 30 September 2015 and report associations between birth weight and renal function. Blood (glomerular filtration rate (GFR)) and urine (microalbuminuria/albumin excreation rate (AER)/urinary albumin creatinine ratio (ACR)) parameters were used to define CKD. Three different effect size estimates were used (odds ratio, regression coefficient and mean difference). The odds of developing CKD in the life course among those born LBW was 1.77 (95% CI: 1.42, 2.20) times and 1.68 (1.27, 2.33) times, assessed by blood and urine parameters respectively. Higher risk was also observed among Asian and Australian populations (blood: OR 2.68; urine: OR 2.28), individuals aged ≤30 years (blood: OR 2.30; urine: OR 1.26), and ≥50 years (blood: OR 3.66; urine: OR 3.10), people with diabetes (blood: OR 2.51), and aborigines (urine: OR 2.32). There was no significant association between HBW and CKD. For every 1 kg increase in BW, the estimated GFR increased by 2.09 mL/min per 1.73 m(2) (1.33-2.85), and it was negatively associated with LogACR (ß -0.07, 95% CI: -0.14, 0.00). LBW inborn had lower mean GFR -4.62 (-7.10, -2.14) compared with normal BW. Findings of this study suggest that LBW increased the risk of developing CKD, and HBW did not show any significant impact.

Cardiovascular Alterations and Multiorgan Dysfunction After Birth Asphyxia

The cardiovascular response to asphyxia involves redistribution of cardiac output to maintain oxygen delivery to critical organs such as the adrenal gland, heart, and brain, at the expense of other organs such as the gut, kidneys and skin. This redistribution results in reduced perfusion and localized hypoxia/ischemia in these organs, which, if severe, can result in multiorgan failure. Liver injury, coagulopathy, bleeding, thrombocytopenia, renal dysfunction, and pulmonary and gastrointestinal injury all result from hypoxia, underperfusion, or both. Current clinical therapies need to be considered together with therapeutic hypothermia and cardiovascular recovery.

Are low birth weight neonates at risk for suboptimal renal growth and function during infancy?

Background

To assess the renal growth and function of neonates during infancy in relation to birth weight and gestational age.

Methods

A longitudinal study was conducted at a tertiary hospital in South India from June 2010 to August 2014. Low birth weight neonates (LBW) were further sub-classified based on gestational age and compared with normal birth weight (NBW) full term neonates at birth, 6 months and 18-24months of age. The renal volume was measured by ultrasound and renal function by Cystatin C- derived glomerular filtration rate (CysGFR) at the three time points during the dynamic phase of renal maturation in infancy.

Results

We recruited 100 LBW and 66 NBW term neonates. Thirty five percent of the LBW neonates were SGA. Among the AGA neonates, 39 % were LBW neonates. The mean height and weight of the LBW neonates were significantly lower compared to NBW neonates throughout infancy. The increment in kidney volume was in accordance with the change in body size, being lower in LBW compared to NBW infants. The combined kidney volume was significantly lower in LBW and SGA neonates across all three time points (p < 0.001). CysGFR in the LBW and SGA infants, despite having low kidney volumes, were comparable to the GFRs of NBW and AGA neonates at the end of infancy.

Conclusion

This study highlights the fact that both birth weight and gestational age influence kidney growth and function in infancy. At the end of infancy, despite a significant difference in kidney volumes and age at last follow up, the glomerular filtration rate was comparable between LBW and NBW infants. Though not statistically significant, there was a trend towards higher urine microalbumin in LBW compared to NBW in infancy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0314-7) contains supplementary material, which is available to authorized users.

The Real-World Routine Use of Caffeine Citrate in Preterm Infants: A European Postauthorization Safety Study

BACKGROUND

Caffeine citrate is the treatment of choice for apnea of prematurity (AOP). Regulatory agencies have requested real-world data on drug utilization and safety, a postauthorization safety study, of a pharmaceutical-grade caffeine citrate, Peyona, to confirm its benefit for preterm infants.

OBJECTIVES

To investigate the clinical use, outcomes, and safety profile of this pharmaceutical-grade caffeine citrate in the routine treatment of preterm infants with a gestational age (GA) <37 weeks.

METHODS

We conducted a multicenter, noninterventional, prospective study in five European countries. Patients eligible for study enrollment were <37-week GA neonates who received treatment with the pharmaceutical-grade caffeine citrate and whose parents had given informed consent.

RESULTS

A total of 506 preterm infants were enrolled from 21 institutions. The pharmaceutical-grade caffeine citrate doses were administered intravenously, orally, or via both routes. The main indication of use was AOP treatment (58%) followed by AOP prophylaxis (37%). Median treatment duration was 21 days. The primary cause of study termination was AOP resolution (n = 407; 80%). Hundred and six patients (21%) required supplemental oxygen on day 28; 48 patients (9.5%) had bronchopulmonary dysplasia at 36 weeks' postmenstrual age. Twenty-three adverse drug reactions were observed in 21 neonates (4.2%); the most frequent was tachycardia (2.3%) and only one (seizures) was considered serious. Thirty-one patients (8.1%) had hepatic or renal functional impairment; the side effects were manageable, and these patients also benefitted from treatment.

CONCLUSIONS

The use of this caffeine citrate is safe for the management of AOP in a real-world setting.

Variables affecting adolescent renal function in patients born with vesico-ureteric reflux

OBJECTIVE

To examine whether factors in a child's perinatal history influence renal function in adolescence, using a cross-sectional study, as during the past two decades researchers have tried to ascertain whether factors such as low birth weight might be related to a decline in kidney function in adolescence, although published data for children born with vesico-ureteric reflux (VUR) remain insufficient.

PATIENTS AND METHODS

Sixty-one children (20 boys and 41 girls), born between 1985 and 1989 in Greece and diagnosed with VUR, were assessed. A detailed personal and family history was taken and basic anthropometric variables were measured. Kidney function was calculated from serum creatinine levels, and the glomerular filtration rate (GFR), fractional excretion of sodium, albumin levels in urine, creatinine clearance, cystatin C level and the dimensions of each kidney were measured.

RESULTS

The results showed a positive relationship of birth weight (P = 0.01) with blood pressure in adolescence in children diagnosed with any degree of VUR. Renal function seemed to be intact whatever the cause of VUR, the volume of the kidneys in adolescence (P = 0.386 and 0.483, respectively, for the right and left kidney) and the values of GFR (P = 0.105), creatinine clearance (P = 0.213) and cystatin C (P = 0.055).

CONCLUSIONS

These results showed that although there is a positive association between blood pressure in adolescence and birth weight, in children born with VUR there was no deterioration in renal function. Kidneys seem to function normally regardless of the gestational age at birth.

The interplay between drugs and the kidney in premature neonates

The kidney plays a central role in the clearance of drugs. However, renal drug handling entails more than glomerular filtration and includes tubular excretion and reabsorption, and intracellular metabolization by cellular enzyme systems, such as the Cytochrome P450 isoenzymes. All these processes show maturation from birth onwards, which is one of the reasons why drug dosing in children is not simply similar to dosing in small adults. As kidney development normally finishes around the 36th week of gestation, being born prematurely will result in even more immature renal drug handling. Environmental effects, such as extra-uterine growth restriction, sepsis, asphyxia, or drug treatments like caffeine, aminoglycosides, or non-steroidal anti-inflammatory drugs, may further hamper drug handling in the kidney. Dosing in preterm neonates is therefore dependent on many factors that need to be taken into account. Drug treatment may significantly hamper postnatal kidney development in preterm neonates, just like renal immaturity has an impact on drug handling. The restricted kidney development results in a lower number of nephrons that may have several long-term sequelae, such as hypertension, albuminuria, and renal failure. This review focuses on the interplay between drugs and the kidney in premature neonates.

Effect of maternal protein restriction on liver metabolism in rat offspring

Consequences of gestational protein restriction (GPR) on liver metabolism in rat offspring were investigated. Pregnant dams were divided into groups: normal (NP, 17% casein) or low-protein diet (LP, 6% casein). Livers were collected from 30-day-old offspring (d30) for analysis or isolation of mitochondria. At d30, hepatic and muscle glycogen was increased in LP group. Mitochondrial swelling and oxygen uptake (recorded with a Clark-type electrode) were significantly reduced in NP female and LP pups. Thiobarbituric acid reactive substances production was lower in females (NP or LP), suggesting significant inhibition of lipid peroxidation. Measurement of mitochondrial respiration (states 3 and 4 stimulated by succinate) showed a higher ADP/O ratio in LP pups, particularly females, suggesting higher phosphorylation efficiency. In the 1st month of life, under our experimental conditions, GPR protects liver mitochondria against oxidative stress and females seem to be more resistant or more suitable for survival.

Long-term renal consequences of preterm birth

The normal development of the kidney may be affected by several factors, including abnormalities in placental function, resulting in fetal growth restriction, exposure to maternal disease states, including hypertension and diabetes, antenatal steroids, chorioamnionitis, and preterm delivery. After preterm birth, several further insults may occur that may influence nephrogenesis and renal health, including exposure to nephrotoxic medications, postnatal growth failure, and obesity after growth restriction. In this review article, common clinical neonatal scenarios are used to highlight these renal risk factors, and the animal and human evidence on which these risk factors are based are discussed.

Is late-preterm birth a risk factor for hypertension in childhood?

Late-preterm birth is associated with higher rates of neonatal morbidity and mortality and higher health care utilization, but its impact on later life is not well known. In this study, we aimed to evaluate whether late-preterm birth affects blood pressure, renal function, and urinary protein excretion in children later in life. Sixty-five children aged 4 to 13 years born as late-preterm and 65 age- and sex-matched children born full term were evaluated with 24-h ambulatory blood pressure monitoring (ABPM), urinary microalbumin excretion (UAE), and glomerular filtration rate (GFR). All subjects underwent ABPM prospectively. For each gender, daytime, nighttime, and 24-h systolic and diastolic and mean blood pressures (SBP, DBP, and MAP) were transformed to standard deviation scores (SDS). Blood pressure profiles (SBP DBP, and MAP) were considered abnormal when the corresponding SDS values exceeded 1.63. Urinary microalbumin excretion was expressed as milligrams per day, and the value between 30 and 300 mg/day was defined as microalbuminuria (MA). There was no significant difference in the mean GFR and MA levels between late-preterm and term children. 24-h systolic BP SDS, daytime systolic BP SDS, nighttime systolic BP SDS, 24-h diastolic BP SDS, nighttime diastolic BP SDS, 24-h MAP BP SDS, daytime MAP BP SDS, and nighttime MAP BP SDS were found to be significantly higher in late-preterm children compared to term children.

CONCLUSION

We conclude that late-preterm children have higher BP levels, so those children should be followed up carefully by the pediatrician regarding probable hypertension in their future life.

Evaluation of renal functions in preterm infants with respiratory distress syndrome

BACKGROUND

The aim of this prospective study was to evaluate urinary glutathione S transferases π (GST-π), beta-2-microglobulin (B2-MG), and N-acetyl-β-d-glucosaminidase (NAG) levels as markers revealing the effect of respiratory distress syndrome (RDS) on renal function in preterm infants.

METHODS

The study was performed with 76 preterm infants whose gestational ages were between 28 and 32 weeks. Twenty-six preterm infants with RDS (cases) and 50 preterm infants without RDS (controls) enrolled in the study. Blood and urine samples were obtained on postnatal (PN) day 3 and 30. Urinary GST-π levels were measured by enzyme-linked immunosorbent assay (ELISA), and urinary B2-MG levels were determined by nephelometric method.

RESULTS

There was no significant difference in urinary B2-MG and GST-π levels between RDS and non-RDS groups on PN day 3 (P > 0.05 for each). However, preterm infants with RDS had significantly higher urinary B2-MG and GST-π levels than the control group on PN day 30 (P = 0.0001 and P = 0.031, respectively). Urinary NAG levels were higher in RDS group than those of the controls on both PN day 3 and 30, but these findings were not statistically significant (P > 0.05, for each).

CONCLUSION

Preterm infants with RDS had increased levels of both GST-π and B2-MG levels on PN day 30, suggesting subclinical tubular dysfunction, probably secondary to hypoxic stress.

Neonatal renal physiology

The renal system plays a tremendous role in growth and development of infants and children. The kidney itself also undergoes a maturation process as it transitions from the fetal to the extrauterine environment. Renal function continues to undergo further adaptive changes in the neonatal period. It is important for the clinician caring for neonates to be aware of the expected fluid shifts, electrolyte handling, and renal functional capacity as these "normal" changes will become quite relevant when medical or surgical pathology is present. The preterm neonates are especially vulnerable due to their functionally immature kidneys. Renal function in the preterm neonate is not only immature at birth but there is a significant delay in the renal function to achieve its full capacity. This review highlights the physiologic adaptations of the kidney and its effects on the body during the neonatal period.

Clinical pharmacology of furosemide in neonates: a review

Furosemide is the diuretic most used in newborn infants. It blocks the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb of the loop of Henle increasing urinary excretion of Na⁺ and Cl⁻. This article aimed to review the published data on the clinical pharmacology of furosemide in neonates to provide a critical, comprehensive, authoritative and, updated survey on the metabolism, pharmacokinetics, pharmacodynamics and side-effects of furosemide in neonates. The bibliographic search was performed using PubMed and EMBASE databases as search engines; January 2013 was the cutoff point. Furosemide half-life (t_1/2) is 6 to 20-fold longer, clearance (Cl) is 1.2 to 14-fold smaller and volume of distribution (Vd) is 1.3 to 6-fold larger than the adult values. t_1/2 shortens and Cl increases as the neonatal maturation proceeds. Continuous intravenous infusion of furosemide yields more controlled diuresis than the intermittent intravenous infusion. Furosemide may be administered by inhalation to infants with chronic lung disease to improve pulmonary mechanics. Furosemide stimulates prostaglandin E2 synthesis, a potent dilator of the patent ductus arteriosus, and the administration of furosemide to any preterm infants should be carefully weighed against the risk of precipitation of a symptomatic patent ductus arteriosus. Infants with low birthweight treated with chronic furosemide are at risk for the development of intra-renal calcifications.

Early life influences kidney function at age 63-64 years, but so does adult body size: results from the newcastle thousand families birth cohort

BACKGROUND

It is suggested that impaired fetal growth can affect kidney development, resulting in fewer glomeruli being formed and reduced kidney function later in life. The aim of this study was to investigate early life variables in relation to adult kidney function, and compare these to the influence of later life variables.

METHODS

Detailed information was collected prospectively regarding 1,142 babies, born in 1947 in Newcastle upon Tyne. At the age of 63-64 years, 335 participants had serum creatinine successfully measured and completed a lifestyle questionnaire. These measurements were used to calculate their estimated glomerular filtration rate (eGFR).

RESULTS

Body mass index (BMI) and being female were significantly negatively associated with eGFR. Birth weight was significantly positively associated with eGFR. In sex-specific analyses, BMI and cigarette smoking remained significant for males (n = 154), with a near significant association for birth weight, whereas none of the variables remained significant for females (n = 181).

CONCLUSIONS

The findings suggest that sex, size at birth and BMI may be important variables influencing adult kidney function. However, as only a small amount of variance in eGFR was explained by these variables, additional longitudinal studies would be beneficial for assessing lifecourse influences on kidney function.

Renal function and systolic blood pressure in very-low-birth-weight infants 1-3 years of age

BACKGROUND

Preterm very-low-birth-weight (PT-VLBW) infants are at risk of an elevated systolic blood pressure (SBP) in infancy and adulthood; however, the pathogenesis remains unclear. Altered renal development or function may be associated with increased SBP, but their contribution in PT-VLBW is unknown.

METHODS

We determined renal function and its relationship to SBP in three groups of PT-VLBW at 1, 2, and 3 years of age, using serum cystatin-C to calculate the estimated glomerular filtration rate (eGFR).

RESULTS

Cystatin-C levels decreased from 0.84 ± 0.2 (SD) within the 1-year group to 0.70 ± 0.1 mg/l (±SD; P < 0.001) at 3 years and were unrelated to gender, fetal growth, and neonatal indomethacin exposure. eGFR rose from 121 ± 59 in the 1-year group to 138 ± 21 ml/min · 1.73 m(2) (P < 0.001) at 3 years. At 1 year, cystatin-C levels decreased with increasing SBP (P < 0.007), and infants with SBP ≥ 90 th% had lower cystatin-C and higher eGFR (P < 0.05). At 3 years, infants with lower birth weight (P < 0.03) and gestational age (P = 0.06) had reduced eGFR.

CONCLUSIONS

Preterm very-low-birth-weight infants demonstrate increasing renal function with advancing age. An elevated SBP and eGFR at 1 year suggests dysfunctional renal autoregulation and hyperfiltration, which may alter subsequent renal function and contribute to the lower eGFR seen at 3 years in infants with the lowest birth weight and gestational age.

Low Birth Weight due to Intrauterine Growth Restriction and/or Preterm Birth: Effects on Nephron Number and Long-Term Renal Health

Epidemiological studies have clearly demonstrated a strong association between low birth weight and long-term renal disease. A potential mediator of this long-term risk is a reduction in nephron endowment in the low birth weight infant at the beginning of life. Importantly, nephrons are only formed early in life; during normal gestation, nephrogenesis is complete by about 32–36 weeks, with no new nephrons formed after this time during the lifetime of the individual. Hence, given that a loss of a critical number of nephrons is the hallmark of renal disease, an increased severity and acceleration of renal disease is likely when the number of nephrons is already reduced prior to disease onset. Low birth weight can result from intrauterine growth restriction (IUGR) or preterm birth; a high proportion of babies born prematurely also exhibit IUGR. In this paper, we describe how IUGR and preterm birth adversely impact on nephrogenesis and how a subsequent reduced nephron endowment at the beginning of life may lead to long-term risk of renal disease, but not necessarily hypertension.

Preterm birth and the kidney: implications for long-term renal health

Although the majority of preterm neonates now survive infancy, there is emerging epidemiological evidence to demonstrate that individuals born preterm exhibit an elevated risk for the development of hypertension and renal impairment later in life, thus supporting the developmental origins of health and disease hypothesis. The increased risk may potentially be attributed to a negative impact of preterm birth on nephron endowment. Indeed, at the time when most preterm neonates are delivered, nephrogenesis in the kidney is still ongoing with the majority of nephrons normally formed during the third trimester of pregnancy. A number of clinical studies have provided evidence of altered renal function during the neonatal period, but to date there have been limited studies describing the consequences of preterm birth on kidney structure. Importantly, studies in the preterm baboon have shown that nephrogenesis is clearly ongoing following preterm birth; however, the presence of abnormal glomeruli (up to 18% in some cases) is of concern. Similar glomerular abnormalities have been described in autopsied preterm infants. Prenatal and postnatal factors such as exposure to certain medications, hyperoxia and intrauterine and/or extrauterine growth restriction are likely to have a significant influence on nephrogenesis and final nephron endowment. Further studies are required to determine the factors contributing to renal maldevelopment and to identify potential interventional strategies to maximize nephron endowment at the start of life, thereby optimizing long-term renal health for preterm individuals.

Acute kidney injury post neonatal asphyxia

Acute kidney injury (AKI) is a common consequence of perinatal asphyxia, occurring in up to 56% of these infants. A major difficulty in diagnosing this condition is the lack of a consensus definition of neonatal AKI, largely because of a dearth of specific measurable variables and biochemical markers. This review will discuss the current evidence regarding the epidemiology, investigation, and treatment of AKI in the asphyxiated neonate. Particular emphasis will be given to the investigation of renal function in the neonate and to potential biomarkers that may aid the clinician in the diagnosis of renal injury in this population.

Renal programming: cause for concern?

Development of the kidney can be altered in utero in response to a suboptimal environment. The intrarenal factors that have been most well characterized as being sensitive to programming events are kidney mass/nephron endowment, the renin-angiotensin system, tubular sodium handling, and the renal sympathetic nerves. Newborns that have been subjected to an adverse intrauterine environment may thus begin life at a distinct disadvantage, in terms of renal function, at a time when the kidney must take over the primary role for extracellular fluid homeostasis from the placenta. A poor beginning, causing renal programming, has been linked to increased risk of hypertension and renal disease in adulthood. However, although a cause for concern, increasingly, evidence demonstrates that renal programming is not a fait accompli in terms of future cardiovascular and renal disease. A greater understanding of postnatal renal maturation and the impact of secondary factors (genes, sex, diet, stress, and disease) on this process is required to predict which babies are at risk of increased cardiovascular and renal disease as adults and to be able to devise preventative measures.

Low birthweight and chronic kidney disease

Low birthweight reflects the congenital defects of organs, which is associated with chronic kidney disease through its direct influence on nephron number and function, also through related metabolic disease-induced kidney damage. We reviewed the current evidence regarding the role of low birthweight in the pathogenesis of chronic kidney disease.

Renal function and volume of infants born with a very low birth-weight: a preliminary cross-sectional study

AIM

The aim of our study was to compare the function and volumes of kidneys of very low birth-weight (VLBW) and of extremely low birth-weight (ELBW) infants at pre-school ages.

PATIENTS AND METHODS

We did a revision of the neonatal records of infants born in our hospital that weighed < or =1500 g at birth. The children were divided into two groups according to their weight at birth: ELBW (<1000 g) and VLBW (1000-1500 g). At the age of 5.7 +/- 1.4 years, the children underwent clinical, laboratory and ultrasound renal assessments.

RESULTS

Sixty-nine children fulfilled the requirements for the study. The rate of neonatal treatment with aminoglycosides was higher in ELBW preterms. Renal function parameters, i.e. estimated glomerular filtration rate and albuminuria, did not differ between the two groups of children. Urinary alpha1-microglobulin excretion was significantly higher and kidneys were significantly smaller in the ELBW group than in the VLBW group.

CONCLUSION

No impairment or differences in renal parameters were found in pre-school children born ELBW compared with those born with VLBW, except for differences in kidney volume, renal cortical thickness and urinary alpha1-microglobulin excretion. Thus, patients born with ELBW would require a longer follow-up period.

Drug transporters and renal drug disposition in the newborn

The individual response to a drug in terms of drug efficacy and toxicity is highly variable; this represents a major problem in clinical practice. Potential causes for such variability include pathogenesis and severity of the disease being treated, drug interactions, patient age, nutritional status, renal and liver function and concomitant illness. Inherited differences in drug metabolism and genetic polymorphism of targets of drug therapy can have even greater influence on the efficacy and toxicity of medications. We will discuss the role of drug transporters (organic anion transporting polypeptides and Pgp), drug-related gene polymorphisms and pathologies, renal function and drug metabolism in a very special patient population, the newborn. Reliable predictions of drug pharmacokinetics in the newborn, derived from an understanding of the transport mechanisms, should allow therapeutic agents to be used more safely in this special population.

Compliance with dosing recommendations from common references in prescribing antibiotics for preterm neonates

PURPOSE

Incorrect dosage was the most common type of medication errors in neonate patients. Different dosing recommendations from common reference sources may have contributed to the errors. This study assesses the compliance rate with the common reference sources in antibiotic dosage prescribed for preterm infants in a neonatal intensive care unit (NICU).

METHODS

A retrospective study using chart review was conducted at a tertiary care medical center with university affiliation in Taiwan. Study subjects were preterm neonates admitted to the NICU of the medical center between 2000 and 2002 and prescribed at least one antibiotic during the stay. Recommendations from three commonly used reference sources (Pediatric Dosage Handbook, Neonatal Drug Formulary, and Neofax) were employed to evaluate the dosage compliance of the antibiotic prescriptions.

RESULTS

A total of 433 preterm infants and 3459 prescriptions were included. Depending on the reference source used, the percentages of antibiotic prescriptions where both the dose and the interval were compliant with recommendations ranged from 36.88 to 87.54%.

CONCLUSIONS

A significant proportion of antibiotics prescribed for preterm neonates in this medical center did not comply with the recommended dosage from common reference sources. Future studies should investigate the clinical impacts of the dosing deviation.

Children's toxicology from bench to bed--Drug-induced renal injury (3): Drug transporters and toxic nephropathy in childhood

The kidney is susceptible to drugs and environmental substances because of its anatomical and functional reasons, one of which is the existence of drug transport systems in proximal tubular cells. Among those, Organic anion transporter family (OAT family) plays the central role in elimination of drugs from the kidney and development of nephrotoxicity. Regarding drug nephrotoxicity in children, development of the child and the kidney should also be taken into account. This review focuses on the mechanisms of toxic nephropathy in children with special attention to the OAT family.

Salt sensitivity of children with low birth weight

Compromised intrauterine fetal growth leading to low birth weight (<2500 g) is associated with adulthood renal and cardiovascular disease. The aim of this study was to assess the effect of salt intake on blood pressure (salt sensitivity) in children with low birth weight. White children (n=50; mean age: 11.3+/-2.1 years) born with low (n=35) or normal (n=15) birth weight and being either small or appropriate for gestational age (n=25 in each group) were investigated. The glomerular filtration rate was calculated using the Schwartz formula, and renal size was measured by ultrasound. Salt sensitivity was assigned if mean 24-hour blood pressure increased by >or=3 mm Hg on a high-salt diet as compared with a controlled-salt diet. Baseline office blood pressure was higher and glomerular filtration rate lower in children born with low birth weight as compared with children born at term with appropriate weight (P<0.05). Salt sensitivity was present in 37% and 47% of all of the low birth weight and small for gestational age children, respectively, higher even than healthy young adults from the same region. Kidney length and volume (both P<0.0001) were reduced in low birth weight children. Salt sensitivity inversely correlated with kidney length (r(2)=0.31; P=0.005) but not with glomerular filtration rate. We conclude that a reduced renal mass in growth-restricted children poses a risk for a lower renal function and for increased salt sensitivity. Whether the changes in renal growth are causative or are the consequence of the same abnormal "fetal programming" awaits clarification.

Renal volume and function in school-age children born preterm or small for gestational age

Impaired renal development during foetal life is a proposed mechanism for adult hypertension in people born small. Whether preterm birth contributes to such adverse development is still unclear. We investigated the selective contributions from foetal growth restriction or preterm birth to renal function and volume in children with low birth weight. Three groups of 9 to 12-year-old children were studied: those born at < 32 gestational weeks (preterm, n = 39), those born at term but small for gestational age (SGA, n = 29) and those born at the term appropriate for gestational age (controls, n = 37). We estimated renal function by calculating glomerular filtration rate (GFR) and by measuring urinary proteins. Volumetric ultrasound of the kidneys was performed in 86 children (preterm, n = 33; SGA, n = 25; controls, n = 29). Estimated glomerular filtration rate (eGFR) and urinary protein patterns were similar between the groups. Kidney volume (preterm 162 ml (31); SGA 163 ml (26) and controls 182 ml (47)) was smaller in the preterm group than in the controls, but the difference was not significant when adjusted for body surface area, gender and age (P = 0.25). Total renal volume correlated to birth weight (r = 0.23, P = 0.03). No significant differences were found in renal function or volume between the three groups at school age.

Bench-to-bedside review: Developmental influences on the mechanisms, treatment and outcomes of cardiovascular dysfunction in neonatal versus adult sepsis

Sepsis is a significant cause of morbidity and mortality in neonates and adults, and the mortality rate doubles in patients who develop cardiovascular dysfunction and septic shock. Sepsis is especially devastating in the neonatal population, as it is one of the leading causes of death for hospitalized infants. In the neonate, there are multiple developmental alterations in both the response to pathogens and the response to treatment that distinguish this age group from adults. Differences in innate immunity and cytokine response may predispose neonates to the harmful effects of pro-inflammatory cytokines and oxidative stress, leading to severe organ dysfunction and sequelae during infection and inflammation. Underlying differences in cardiovascular anatomy, function and response to treatment may further alter the neonate's response to pathogen exposure. Unlike adults, little is known about the cardiovascular response to sepsis in the neonate. In addition, recent research has demonstrated that the mechanisms, inflammatory response, response to treatment and outcome of neonatal sepsis vary not only from that of adults, but vary among neonates based on gestational age. The goal of the present article is to review key pathophysiologic aspects of sepsis-related cardiovascular dysfunction, with an emphasis on defining known differences between adult and neonatal populations. Investigations of these relationships may ultimately lead to 'neonate-specific' therapeutic strategies for this devastating and costly medical problem.

Chronic partial ureteral obstruction and the developing kidney

Although congenital urinary tract obstruction is a common disorder, its pathophysiology remains poorly understood and clinical practice is controversial. Animal models have been used to elucidate the mechanisms responsible for obstructive nephropathy, and the models reveal that renal growth and function are impaired in proportion to the severity and duration of obstruction. Ureteral obstruction in the neonatal rat or mouse leads to activation of the renin-angiotensin system, renal infiltration by macrophages, and tubular apoptosis. Nephrons are lost by glomerular sclerosis and the formation of atubular glomeruli, and progressive injury leads to tubular atrophy and interstitial fibrosis. Recovery following release of obstruction depends on the timing, severity, and duration of obstruction. Growth factors and cytokines are produced by the hydronephrotic kidney, including MCP-1 and TGF-beta1, which are excreted in urine and can serve as biomarkers of renal injury. Because MRI can be used to monitor renal morphology, blood flow, and filtration rate, its use might supplant current imaging modalities (ultrasonography and diuretic renography), which have significant drawbacks. Combined use of MRI and new urinary biomarkers should improve our understanding of human congenital obstructive nephropathy and should lead to new approaches to evaluation and management of this challenging group of patients.

Impact de l'âge gestationnel et du poids de naissance sur le devenir cardiovasculaire à long terme

PURPOSE

Intra-uterine growth restriction and preterm birth can lead to cardiovascular diseases in adulthood.

CURRENT KNOWLEDGE AND KEY POINTS

Preterm birth and intra-uterine growth restriction induce long-term changes in organ development such as arterial system and kidney function. Among these changes, the impairment of arterial wall structure or properties occurring in low birth weight babies, as a result of preterm birth and intra-uterine growth restriction, may lead on a long-term to an elevation of arterial pressure and arterial stiffness. These notions are still not completely understood and seem of high importance in regard to the high frequency in preterm birth and intra-uterine growth restriction.

FUTURE PROSPECTS AND PROJECTS

Identifying clinical, paraclinical markers and better understanding a link between adverse perinatal conditions and cardiovascular diseases might improve actions for preventing cardiovascular diseases in adulthood in this population.

Angiotensin AT1-receptor inhibition exacerbates renal injury resulting from partial unilateral ureteral obstruction in the neonatal rat

The renin-angiotensin system is activated in the developing kidney and is necessary for normal renal development, but is further activated by unilateral ureteral obstruction (UUO). During nephrogenesis, there is a switch from a preponderance of angiotensin AT(2) to AT(1) receptors in the rat. We examined the renal cellular response to angiotensin II receptor inhibition in the neonatal rat subjected to partial UUO under anesthesia within 48 h of birth. Group I ("early") received saline vehicle, losartan (AT(1) inhibitor), or PD-123319 (AT(2) inhibitor) during the completion of nephrogenesis in the first 10 days of life. Group II ("late") received each of the three treatments throughout the subsequent 10 days of life. Kidneys were harvested at 21 days, and the distribution of renin, apoptosis, macrophages, alpha-smooth muscle actin, and collagen was determined. Losartan and PD-123319 each increased vascular renin distribution in both kidneys. Partial UUO reduced growth and increased apoptosis, macrophages, alpha-smooth muscle actin, and collagen in the obstructed kidney. Early losartan treatment further increased alpha-smooth muscle actin and collagen in the obstructed kidney and induced apoptosis, macrophages, and collagen in the contralateral kidney. Late losartan treatment had no effect on any of the parameters in either kidney, and PD-123319 had no effect on either kidney. We conclude that selective inhibition of AT(1) receptors during nephrogenesis (but not during subsequent renal maturation) exacerbates injury to the obstructed kidney and also injures the contralateral kidney. These results suggest that angiotensin II receptor blockers should be avoided in the developing hydronephrotic kidney.

Angiotensin-converting enzyme inhibition aggravates renal interstitial injury resulting from partial unilateral ureteral obstruction in the neonatal rat

Congenital urinary tract obstruction is the most important cause of renal insufficiency in infants and children, and angiotensin-converting enzyme (ACE) inhibitors attenuate the progression of renal disease in adults. ACE inhibitors are increasingly utilized in children with progressive renal disease. Because angiotensin is necessary for normal renal development, we examined the effects of ACE inhibition both during and immediately following the period of postnatal nephrogenesis in the neonatal rat subjected to sham operation or partial unilateral ureteral obstruction (UUO) under general anesthesia within the first 48 h of life. Rats in group I received enalapril 30 mg/kg body wt (or vehicle) daily for the first 10 days, while in group II, the 10 days of treatment began 10 days after surgery. Kidneys were harvested at day 21 and analyzed for apoptosis (TUNEL), interstitial macrophages (ED-1 immunohistochemistry), myofibroblasts (alpha-smooth muscle actin), and collagen (Sirius red). Partial UUO delayed glomerular maturation and increased ipsilateral renal macrophage infiltration, alpha-smooth muscle actin and Sirius red staining. In group I, enalapril increased myofibroblast accumulation in sham-operated kidneys, but not in obstructed kidneys. In contrast, in group II, enalapril further increased macrophage, myofibroblast, and collagen accumulation following partial UUO. The relative abundance of components of the kallikrein-kinin system, measured by Western blot, was not altered by partial UUO in the 14- and 28-day-old rat. Thus, in contrast to its salutary effects at later ages, ACE inhibition can worsen injury to the partially obstructed kidney during renal maturation even after the completion of nephrogenesis.

Consequences of Intrauterine Growth Restriction for the Kidney

Low birth weight due to intrauterine growth restriction is associated with various diseases in adulthood, such as hypertension, cardiovascular disease, insulin resistance and end-stage renal disease. The purpose of this review is to describe the effects of intrauterine growth restriction on the kidney. Nephrogenesis requires a fine balance of many factors that can be disturbed by intrauterine growth restriction, leading to a low nephron endowment. The compensatory hyperfiltration in the remaining nephrons results in glomerular and systemic hypertension. Hyperfiltration is attributed to several factors, including the renin-angiotensin system (RAS), insulin-like growth factor (IGF-I) and nitric oxide. Data from human and animal studies are presented, and suggest a faltering IGF-I and an inhibited RAS in intrauterine growth restriction. Hyperfiltration makes the kidney more vulnerable during additional kidney disease, and is associated with glomerular damage and kidney failure in the long run. Animal studies have provided a possible therapy with blockage of the RAS at an early stage in order to prevent the compensatory glomerular hyperfiltration, but this is far from being applicable to humans. Research is needed to further unravel the effect of intrauterine growth restriction on the kidney.

Tubular proteinuria in pre-term and full-term infants

Predictors of tubular proteinuria (alpha 1-M/crea ratio >10 mg/mmol) were sought in 100 infants of 24-32 weeks' (group 1) and 69 of 34-42 weeks' gestation (group 2). Random spot urine samples were obtained in the former group at the ages of 0-3 days, at 1-2 weeks and thereafter at 2-week intervals until the disappearance of tubular proteinuria, and in the latter one sample at a mean (SD) of 3.0 days' (1.3) age. In group 1, gestational age correlated negatively with the first urinary alpha 1-M/crea ratio. The highest urinary alpha 1-M/crea ratios [median (range) 39.1 mg/mmol (9.5-268.9)] occurred at a median (range) of 5 days' (1-42) age. Low gestational age and the need for inotropes predicted tubular proteinuria early after birth, whereas low gestation and long duration of ventilator treatment predicted the highest alpha 1-M/crea ratios. Prolonged vancomycin treatment and low gestational age were associated with delayed normalization of tubular proteinuria. In group 2 no significant risk factors for tubular proteinuria were found. The urinary alpha 1-M/crea ratio seems to be a sensitive indicator of renal tubular function in neonates, with low gestational age, the need for inotropes and prolonged assisted ventilation being predictors of increased tubular proteinuria. Long vancomycin courses should be avoided in pre-term infants in view of the prolonged adverse renal effects.

Long-term renal follow-up of extremely low birth weight infants

There is evidence that low birth weight caused by intrauterine growth retardation adversely affects normal renal development. Very little information on this issue is available on children born very prematurely. This investigation examined clinical and functional renal parameters in 40 children (23 boys, 17 girls) ranging in age between 6.1 and 12.4 years and weighing less than 1000 g at birth. Results were compared to those obtained in 43 healthy children of similar age and gender. Study subjects were significantly smaller and thinner than control subjects (mean height SDS: -0.36 vs. +0.70; and mean BMI SDS: -0.56 vs. +1.18). Systolic, diastolic, and mean blood pressures did not differ from those of controls. Renal sonography revealed no abnormality, and mean percentiles for renal length and volume appeared normal. In comparison with controls, plasma creatinine concentration (0.62+/-0.1 vs. 0.53+/-0.1 mg/dl) and estimated creatinine clearance (117+/-17 vs. 131+/-17 ml min(-1) 1.73 m(-2)) differed significantly. No significant differences were observed in microalbuminuria values, but five study subjects (12.5%) presented values above the upper limit of normality. A defect in tubular phosphate transport was also evident: TmP/GFR (3.6+/-0.4 vs. 4.2+/-0.8 mg/dl) and TRP (83+/-5% vs. 90+/-4%) were significantly lower, and urinary P excretion, estimated by the ratio UP/UCr, was significantly higher (1.2+/-0.4 vs. 0.9+/-0.4 mg/mg) than controls. Urinary calcium excretion, estimated by the UCa/UCr ratio, was also significantly higher (0.15+/-0.07 vs. 0.12+/-0.09 mg/mg). These data clearly demonstrate that both GFR and tubular phosphate transport are significantly diminished in school-age children born with extreme prematurity, probably as a consequence of impaired postnatal nephrogenesis.