Renal Handling of Albumin and Beta-2-Microglobulin in Neonates

Abstract

Urinary albumin and β₂-microglobulin (B₂M) were measured during the neonatal period. Urinary albumin decreased postnatally in term neonates, while it remained almost constant in preterm neonates. Urinary B₂M showed a peak level on day 7 both in term and preterm neonates. There was some trend towards higher levels of albumin and B₂M with decreasing gestation, showing that glomerular permeability increases and proximal tubular protein reabsorption decreases with increasing degrees of prematurity. In sick preterms who were depressed at birth and had respiratory failure, both parameters were elevated during the first 2 weeks, indicating the presence of glomerular and tubular damage in this period. The changes in B₂M with gestation or clinical condition were more pronounced than those in albumin.

Assessment of renal functional maturation and injury in preterm neonates during the first month of life

“…Very low concentrations of both high-molecular-weight (HMW) and low-molecular-weight (LMW) proteins are normally present in the urine, due to the function of the glomerular filtration barrier and the reuptake of filtered proteins in the proximal tubule (28,32). A limited number of previous studies have demonstrated a high variation in urine albumin levels between individual preterm neonates (7,10), with the highest levels exhibited by those with a low gestational age at birth and those that are clinically unstable (3,7,10,11,52). Urinary levels of ␤2-microglobulin (␤2-M) have also been shown to be significantly greater in the preterm infant compared with term-born infants throughout the first month of life (2,52,53), and they decrease with increasing gestational and postnatal age (50).…”

Preterm Birth and/or Factors that Lead to Preterm Delivery: Effects on the Neonatal Kidney

“…Alternatively, high levels of low molecular weight proteins (such as β2-microglobulin) are indicative of reduced reuptake by the proximal tubule cells [45,46]. The occurrence of proteinuria in neonates is strongly linked to gestational age at birth with studies in preterm infants reporting significantly greater albumin and β2-microglobulin concentrations over the first month of life in infants born <32 weeks gestation, compared to neonates born >32 weeks gestation [39,47]. To date, it remains unclear whether the observed proteinuria in preterm infants is a result of their renal immaturity or due to postnatal renal injury.…”

Effects of Preterm Birth on the Kidney

“…In the preterm neonate, few studies have been conducted to examine urine protein excretion. In general, there is a high variability in urine albumin levels between individual neonates (Clark et al, 1989;Fell et al, 1997), with the highest levels exhibited by those with a low gestational age at birth and those that are clinically unstable (Galaske, 1986;Clark et al, 1989;Tsukahara et al, 1994;Fell et al, 1997;Awad et al, 2002b). The majority of studies have only been conducted during the first week of life following preterm birth.…”

“…The majority of studies have only been conducted during the first week of life following preterm birth. However, in a study by Tsukahara et al (1994) urine albumin levels were assessed in preterm and term neonates over the first 28 days of life. Urine albumin levels were found to remain relatively stable postnatally over the one month period in the term neonates, whereas in the preterm neonates, urine albumin was seen to decrease with increasing postnatal age.…”

“…These findings suggest that the glomerular filtration barrier following preterm birth is structurally immature, until beyond one month of age. Urinary 2-microglobulin levels have also been shown to be significantly greater in the preterm infant compared to term-born infants throughout the first month of life (Aperia et al, 1981;Tsukahara et al, 1990;Tsukahara et al, 1994), and are decreased with increasing gestational and postnatal age (Takieddine et al, 1983). Similarly, levels of 1-microglobulin and RBP are higher in preterm neonates than neonates born at term (Clark et al, 1989;Fell et al, 1997;Awad et al, 2002a).…”