Renal handling of beta-2-microglobulin in the human neonate

Maturation of Glomerular Filtration Rate in Term-Born Neonates: An Individual Participant Data Meta-Analysis

Background: The evidence from individual studies to support the maturational pattern of glomerular filtration rate (GFR) in healthy term-born neonates is inconclusive. We performed an individual participant data (IPD) meta-analysis of reported measured GFR (mGFR) data aimed to establish neonatal GFR reference values. Furthermore, we aimed to optimise neonatal creatinine-based GFR estimations Methods: We identified studies reporting mGFR measured by exogenous markers or creatinine clearance (CrCL) in healthy term-born neonates. The relationship between postnatal age and clearance was investigated using cubic splines with generalized additive linear mixed models. From our reference values, we estimated an updated coefficient for the Schwartz equation (eGFR(ml/min/1.73m²)=(k*height (cm))/serum creatinine(mg/dl)). Results: Forty-eight out of 1521 screened articles reported mGFR in healthy term-born neonates, and 978 mGFR values from 881 neonates were analysed. IPD were available for 367 neonates and the other 514 neonates were represented by 41 aggregated data points as means/medians per group. GFR doubled in the first five days after birth from 19.6 (95%CI 14.7;24.6) ml/min/1.73m² to 40.6 (95%CI 36.7;44.5) ml/min/1.73m², then more gradually increased to 59.4 (95%CI 45.9;72.9) ml/min/1.73m² by four weeks of age. A coefficient of 0.31 to estimate GFR best fitted the data. Conclusions: These reference values for healthy term-born neonates show a biphasic increase in GFR with the largest increase between days 1 and 5. Together with the re-examined Schwartz equation, this can help identify altered GFR in term-born neonates. To enable widespread implementation of our proposed eGFR equation, validation in a large cohort of neonates is required.

Safety, dosing, and pharmaceutical quality for studies that evaluate medicinal products (including biological products) in neonates

The study of medications among pediatric patients has increased worldwide since 1997 in response to new legislation and regulations, but these studies have not yet adequately addressed the therapeutic needs of neonates. Additionally, extant guidance developed by regulatory agencies worldwide does not fully address the specificities of neonatal drug development, especially among extremely premature newborns who currently survive. Consequently, an international consortium from Canada, Europe, Japan, and the United States was organized by the Critical Path Institute to address the content of guidance. This group included neonatologists, neonatal nurses, parents, regulators, ethicists, clinical pharmacologists, specialists in pharmacokinetics, specialists in clinical trials and pediatricians working in the pharmaceutical industry. This group has developed a comprehensive, referenced White Paper to guide neonatal clinical trials of medicines - particularly early phase studies. Key points include: the need to base product development on neonatal physiology and pharmacology while making the most of knowledge acquired in other settings; the central role of families in research; and the value of the whole neonatal team in the design, implementation and interpretation of studies. This White Paper should facilitate successful clinical trials of medicines in neonates by informing regulators, sponsors, and the neonatal community of existing good practice.

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.

Establishment of a normal reference value for serum β2 microglobulin in Japanese children: reevaluation of its clinical usefulness

OBJECTIVE

Serum β2 microglobulin (β2MG) is considered to be a marker of renal function, which is independently associated with age. However, only a few studies have reported the reference values for β2MG in children thus far, particularly in young children. In this study, we evaluated the distribution of serum β2MG values in healthy Japanese children and assessed its clinical usefulness.

METHOD

The normal reference value of serum β2MG was assessed in serum samples from 1131 normal Japanese children (504 boys and 627 girls; age 0-17 years). To test the validity of the reference value, serum samples from children with various kidney diseases were also examined retrospectively.

RESULTS

The mean values for β2MG were significantly negatively correlated with age (r = -0.47, P < 0.001). No significant difference was observed between the values of boys and girls in any age group. The established β2MG reference range covered 99.7 % of patients with decreased kidney function below 75 % based on their serum creatinine (Cr) value and body length.

CONCLUSION

The newly established β2MG reference value in children can be used to detect kidney impairment in children. Serum β2MG in combination with serum Cr used as markers for predicting glomerular function can provide an accurate detection of kidney dysfunction in children.

Urinary ß2-microglobulin in very preterm neonates with chorioamnionitis

It is important to identify premature infants with prenatal inflammation as it contributes to short- and long-term complications. Our object was to study how prenatal inflammation affects the urinary β(2)-microglobulin (β(2)-MG) level. Preterm neonates were divided based on the presence of chorioamnionitis (CAM) into the CAM (n = 100) and non-CAM groups (n = 117). These were further subdivided into five groups each: 30 preterm neonates of 23-26; 42 neonates of 27-28; 54 neonates of 29-30; 51 neonates of 31-32; and 40 neonates of 33-34 weeks' gestation. The urinary β(2)-MG level within 48 h of birth was significantly higher in the CAM group than in the non-CAM group among the neonates of 23-26 weeks' gestation (18.3 ± 6.9 vs 10.0 ± 5.6 × 10(4) μg/gCr, p = 0.0018) and the neonates of 27-28 weeks' gestation (16.2 ± 10.8 vs 8.8 ± 3.3 × 10(4) μg/gCr, p = 0.0101). However, there was no difference in urinary β(2)-MG level between the CAM and the non-CAM group among the neonates ≥ 29 weeks 'gestation. Moreover, the elevated urinary β(2)-MG level in the neonates ≤ 28 weeks ' gestation with CAM had disappeared by 1 week after birth. The reasons for the increase in urinary β(2)-MG level within 48 h of birth in very preterm neonates (≤ 28 weeks' gestation) with CAM are believed to be not only prematurity, but also prenatal inflammation. It is suggested that the urinary β(2)-MG level during the early postnatal period can identify prenatal inflammation.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Fetal serum concentrations of cystatin C and beta2-microglobulin as predictors of postnatal kidney function

OBJECTIVES

Cystatin C and beta(2)-microglobulin are established serum markers of renal function in children and adults. In contrast to creatinine, diaplacental exchange is minimal. The aim of the study was to establish reference values in fetal serum and to test their efficiency in predicting postnatal kidney function.

STUDY DESIGN

This was a prospective noninterventional study measuring cystatin C and beta(2)-microglobulin by particle-enhanced immunoturbidimetry in excess serum from 129 cordocenteses performed in 84 fetuses. Reference intervals (mean +/- 1.96 SD) were calculated in a subgroup of 54 fetuses without evidence of kidney disease, and these reference values were evaluated in 75 sera from 55 fetuses.

RESULTS

Mean cystatin C was 1.66 +/- 0.202 mg/L (upper limit 2.06), and mean beta(2)-microglobulin was 4.25 +/- 0.734 mg/L. Unlike cystatin C, beta(2)-microglobulin decreased significantly with gestational age so that the upper reference limit was 7.19-0.052 x gestational age in weeks. beta(2)-Microglobulin had higher sensitivity (90.0% vs 63.6%) and cystatin C a higher specificity (91.8% vs. 85.5%) for the prediction of impaired renal function; diagnostic efficiency was equal (87.6% vs. 86.1%). Fetuses with impaired renal function at birth or who were aborted for renal malformations had higher cystatin C concentrations than those in a control group. beta(2)-Microglobulin was increased only in fetuses who were aborted.

CONCLUSION

Fetal serum cystatin C and beta(2)-microglobulin concentrations may be useful predictors of postnatal kidney function.

Effect of diuretics on urinary oxalate, calcium, and sodium excretion in very low birth weight infants

OBJECTIVE

To study the effect of diuretic drugs on urinary oxalate excretion in premature infants, and to examine the relationship between urinary calcium and sodium excretion in premature infants.

METHODOLOGY

We measured urinary oxalate, calcium, and sodium excretion in 32 premature infants at approximately 34 weeks gestational age. Seven infants were receiving furosemide, 5 infants were receiving thiazide, 8 infants were receiving furosemide plus thiazide, and 12 infants who were not receiving diuretics served as controls.

RESULTS

Urinary oxalate to creatinine ratios in infants receiving furosemide (0.48 +/- .26), thiazide (0.54 +/- .20), furosemide plus thiazide (0.44 +/- .19), and control infants (0.51 +/- .43) were similar by analysis of variance (ANOVA). Data expressed as oxalate concentration gave similar results. Urinary calcium to creatinine ratios in infants receiving furosemide (0.81 +/- .30), thiazide (0.54 +/- .25), furosemide plus thiazide (0.75 +/- .49), and control infants (0.37 +/- .25) were similar by ANOVA. The urinary calcium concentration in infants receiving furosemide plus thiazide (0.085 +/- 0.042 mg/mL) was different from control infants (0.044 +/- .023) by ANOVA and Student-Newman-Keuls test. Urinary calcium to creatinine ratio was correlated with sodium to creatinine ratio (r = .751).

CONCLUSION

Urinary oxalate excretion in premature infants is not affected by diuretic drugs. Urinary sodium and calcium excretion are closely linked in sodium supplemented premature infants receiving diuretics. The calciuric effect of furosemide is not decreased by the addition of thiazide in premature infants receiving sodium supplements.

Assessment of serum levels of alpha-1-microglobulin, beta-2-microglobulin, and retinol binding protein in the fetal blood. A method for prenatal evaluation of renal function

The concentrations of alpha-1-microglobulin, beta-2-microglobulin, and retinol binding protein were determined in fetal blood sampled by cordocentesis. The blood values of 126 fetuses without ultrasonographic findings of urinary tract abnormalities as controls were found to be independent of the week of gestation. In nine fetuses affected by a severe bilateral renal dysplasia or agenesis, elevated values of alpha-1-microglobulin but normal values of retinol binding protein were obtained. The authors recommend the determination of alpha-1-microglobulin and, with some restriction, also of beta-2-microglobulin in prenatal renal function diagnosis.

Serum alpha 1-microglobulin and beta 2-microglobulin for the estimation of fetal glomerular renal function

As proteins cannot cross the placenta levels of the microproteins alpha 1-microglobulin (alpha 1MG) and beta 2-microglobulin (beta 2 MG) can be used to assess fetal glomerular renal function. alpha 1MG, beta 2MG and creatinine were routinely determined in cord and maternal blood of 133 newborns [gestational age (GA) 25-42 weeks]. Twenty-nine patients with suspected impaired maternal or fetal renal function were studied separately and two fetuses were studied in utero. The mean fetal beta 2MG concentration fell from 3.87 +/- 0.56 mg/l in the 25-31 weeks GA group to 2.60 +/- 0.50 mg/l in the mature newborn group. alpha 1MG concentration fell from 3.10 +/- 0.51 to 2.25 +/- 0.49 mg/dl. In contrast, the mean maternal beta 1MG concentration rose from 1.73 +/- 0.69 mg/l in the 25-31 weeks GA group to a mean of 1.83 +/- 0.48 mg/l in the mature newborn group; alpha 1MG rose from 3.96 +/- 0.58 to 4.33 +/- 1.6 mg/dl. Maternal and fetal creatinine levels were identical. Fetal microprotein levels fall during intra-uterine development as glomerular filtration rate (GFR) rises. There is no correlation between cord blood and maternal alpha 1MG or beta 2MG concentrations. In 13 children with urological anomalies only 1 had elevated microprotein levels and he later developed renal insufficiency. Determination of microprotein levels in fetal serum can be used to detect severe renal function disturbances and to estimate GFR independently of maternal renal function.

Beta-2-microglobulin in the assessment of renal function in full term newborns following perinatal asphyxia

In order to evaluate the clinical usefulness of serum and urinary beta 2 microglobulin (beta 2-m) determination as a marker of renal damage following perinatal asphyxia, twenty asphyxiated and twenty healthy full term newborns were studied. Renal function was monitored on the first and third day after birth by traditional tests such as creatinine (Cr), endogenous creatinine clearance (Ccr), and fractional Na excretion (FeNa), as well as by serum and urinary beta 2 microglobulin. The value of different tests for the diagnosis of oliguria and of acute renal failure was determined. Eleven asphyxiated neonates developed oliguria and five ARF in contrast to none of the controls. Both traditional tests of renal function, and determinations of beta 2-m with the exception of serum beta 2-m, were significantly different (p less than 0.01) between controls and asphyxiated neonates. When stratified analysis was performed, only serum cr, urinary beta 2-m/cr ratio, and Fe beta 2-m were able to discriminate oliguria from preserved diuresis on the first day of life. For ARF, only Ccr and Fe beta 2-m were different, again on the first day of life. Urinary beta 2-m/creatinine ratio and Fe beta 2-m appear to be more sensitive and specific for the early detection of proximal tubular renal dysfunction following perinatal asphyxia than usual tests of renal function.

Nonoliguric hyperkalemia in the premature infant weighing less than 1000 grams

Eighteen very low birth weight premature infants born before 28 weeks gestation and weighing less than 1000 gm were evaluated prospectively for disturbances in serum electrolyte concentrations and for renal glomerular and tubular functions. Clinically symptomatic hyperkalemia resulting in significant electrocardiographic dysrhythmias developed in eight of these infants; 10 babies remained normokalemic. Peak serum potassium concentration ranged from 6.9 to 9.2 mEq/L in the hyperkalemic group; all potassium values in the normokalemic group were less than 6.6 mEq/L. Indices of renal glomerular function and urine output were similar in both groups; no infant had oliguria. Serum creatinine concentrations were the same in both groups (1.04 +/- 0.16 SD mg/dl in normokalemic vs 1.19 +/- 0.24 mg/dl in hyperkalemic infants, beta less than 0.2 at alpha = 0.05), and glomerular filtration rates did not differ significantly (6.29 +/- 1.78 ml/min/1.73 m2 in normokalemic vs 5.70 +/- 1.94 ml/min/1.73 m2 in hyperkalemic infants, beta less than 0.2 at alpha = 0.05). In contrast, indicators of tubular function revealed a significantly larger fractional excretion of sodium in hyperkalemic infants: 13.9 +/- 5.4% versus 5.6 +/- 0.9% in normokalemic control subjects (p less than 0.001). Hyperkalemic infants also had a tendency toward lower urine concentrations of potassium, although there was no significant difference in their net potassium excretion in comparison with that in the normokalemic group. We speculate that hyperkalemia in the tiny baby is in part the result of immature distal tubule function with a compromise in ability to regulate potassium balance.

Postnatal development of renal function during the first year of life

Several aspects of renal function vary considerably during the 1st year of life and differ markedly from the equivalent values in the adult. Glomerular filtration rate (GFR) increases little, prior to the time an infant reaches a conceptional age of 34 weeks, the point in renal development from which the absolute GFR (ml/min) increases gradually to mature values when linear growth is completed during adolescence. GFR corrected for body size is not comparable with adult normal values until after 12 months of age; therefore, whether GFR is estimated from Scr or measured by timed urine collection, there is no easily recalled range of normal values for infants. One must know the changes in the renal function of normal infants that take place following birth during the 1st year of life. Despite several attempts to do so, renal function during the 1st year of life cannot be assessed from urine flow rate. A urine flow rate of less than 1 ml/kg per hour may be normal and appropriate and may not be harmful either to preterm or full-term infants with normal GFR. Impaired concentrating ability of the neonatal kidney is probably of no clinical significance in all but the most extreme circumstances and is not a major factor in an infant becoming dehydrated, developing hypernatremia or being at greater risk of acute renal injury. Acid-base status in infants must be interpreted appropriately to know when alkali therapy should be introduced to avoid growth failure secondary to true metabolic acidosis. When plasma renin activity is measured in the infant with renal failure of hypertension, one must compare the result with the normal range of values related to postnatal age of normal infants.

Use of beta 2 microglobulin to diagnose tubulo-interstitial renal lesions in children

Fractional excretion (FE) of beta 2 microglobulin (beta 2M) was studied in children with glomerular (N = 114), tubular (N = 50) or other (N = 18) renal diseases. FE-beta 2M (normal less than 0.36%) was significantly (P less than 0.001) lower in glomerular diseases (mean 0.104%) than in tubular lesions (mean 4.27%). Unexpectedly, several patients with glomerular disease were found to have increased values for FE-beta 2M. To determine whether this was due to a tubular component in a primary glomerular disease process, FE-beta 2M was measured in 30 children with various glomerulopathies who underwent renal biopsy. Thirteen of these patients had tubulo-interstitial lesions in addition to their glomerular disease. FE-beta 2M in these patients averaged 3.76% (range 0.14 to 44.6%); only two results were normal. Mean FE-beta 2M in the 17 patients without biopsy evidence of tubulo-interstitial disease was 0.063% (range 0.02 to 0.34%); all values were in the normal range. The types of glomerular diseases in the two groups of patients were similar. Patients with a glomerular lesion complicated by tubulo-interstitial lesions had a poorer prognosis than did those with a pure glomerular disease. The high incidence of tubulo-interstitial lesions in patients with glomerular diseases was unexpected. Our data demonstrates that FE-beta 2M represents a reliable non-invasive method to diagnose such involvement. Measurements of beta 2M also provide a convenient method to follow the course and response to treatment of renal tubular injury.

Evaluation of renal function and acute renal failure in the neonate

The diagnosis of renal dysfunction in the neonate can be a challenging problem for the practicing pediatrician. Although there are real differences in renal function between term and preterm infants, overall function is quite adequate in both groups when fluid intake and environmental conditions are carefully controlled. When confronted with an infant with a pathologic decrease in urine output, the clinician must provide adequate fluid resuscitation for the infant with prerenal oliguria without inducing fluid overload in the infant with established, intrinsic renal failure. In addition, the infant with obstruction to urine flow must be distinguished. This requires careful assessment of physical findings and a few key laboratory determinations. Once the diagnosis of renal failure is made, frequent clinical monitoring with anticipation of potential complications is critical. Long-term management of renal failure in infancy and intervention for suspected urinary tract malformation in the fetus have emerged as difficult medical and ethical problems as our technology has advanced.

Beta 2-microglobulin clearance in neonates: index of tubular maturation

Serum and urinary beta 2-microglobulin (beta 2M) were studied by enzyme immunoassay in 28 normal neonates at day 1 and day 4 of life in relation to gestational age (GA) and postnatal age (PNA). The infants were grouped according to GA; 10 with GA ranging from 32 to 35 weeks (mean 33.5 weeks) and 18 with GA ranging from 36 to 41 weeks (mean 38.3 weeks). Serum beta 2M varied directly with both GA and PNA. When values for serum beta 2M were related to conceptional age (CA), a significant positive correlation was present for all the infants studied (r = 0.68, P less than 0.01). Fractional excretion of beta 2M (FE beta 2M) decreased as a function of both GA and PNA. When a comparison of FE beta 2M was made in infants of all CA, a significant inverse correlation was noted for infants with CA less than or equal to 35 weeks (r = -0.89, P less than 0.001). The fall in FE beta 2M reached a plateau by 36 weeks. The highest FE beta 2M (33%) was observed in infants of 32 weeks CA who had the lowest filtered beta 2M (F beta 2M). No statistically significant relationship between changes in FE beta 2M and fractional urine flow rate was observed within each of the CA categories (infants less than or equal to 35 weeks, r = 0.21, P = 0.28; infants greater than or equal to 36 weeks, r = 0.25, P = 0.18).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal excretion of calcium and phosphate in preterm and term infants

We studied urinary phosphate and calcium excretion in preterm and term infants during the first 3 months of life. The infants were mainly breast-fed, and the average phosphate intake ranged between 0.5 and 1 mmol/kg/day. During the first week of life urinary phosphate excretion was significantly higher in preterm than in term infants, whereas parathyroid hormone values were the same. After the first week of life urinary phosphate and calcium excretion were the same in preterm and term infants. Fractional excretion of phosphate was low (range 1% to 6%). In both groups calcium excretion was low during the first weeks of life, and increased thereafter to 5 and 3 mmol/1.73 m2/day, respectively. The urinary calcium/creatine ratio generally exceeded 2.0 (mmol/mmol) in preterm infants after the second week of life. These results are compatible with a state of relative phosphate deficiency, resulting in an adaptively low urinary phosphate excretion and an inability to form bone minerals, and therefore relatively high urinary calcium excretion.