Renal tubular function, newborn

Tyrosinosis is presumably due to fumarylacetoacetate hydrolase deficiency and has a high prevalence in the French-Canadian population of Quebec. It is associated with abnormal liver function, renal tubular dysfunction, anemia, and vitamin D-resistant rickets. Transient tyrosinemia of the newborn, particularly in premature infants, is the most common form of tyrosinemia in infancy. 

Metabolism and elimination rates are generally lower in neonates than in adults. The elimination half-lives of substances used as indicators of liver function (e.g. bromosulfthalein, bilirubin), for example, are longer in newborns than in adults. Renal clearance has been shown to be lower in neonates than in older children and adults, for all chemical classes lipophilic, hydrophilic, and organic ions (Clewell et al., 2002). Glomerular filtration rate at normal-term birth is about one third of the adult value when expressed on the basis of body surface area and matures in about six months. On the other hand, the tubular reabsorption process reaches adult levels within a few days after birth. 

Renal function is limited at birth because the kidneys are anatomically and functionally immature. In full-term newborns, glomerular filtration rate (GFR) is 10-15 mL/min/m, and in premature infants the GFR is only 5-10 mL/min/m. GFR doubles by 1 week of age, because of a postnatal drop in renal vascular resistance and increase in renal blood flow, and reaches adult values by 1 year of age (Figure 23.6) (40,41). A glomerular/tubular imbalance is present in newborns, because glomerular function matures more... 

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