Níveis urinários da proteína transportadora do retinol em uma população pediátrica: evolução em função da idade

Abstract

Objective

To evaluate the behavior of retinol-binding protein (RBPu) in children to establish a reference interval and verify possible differences according to age.The kidney of a child, especially a newborn , is singularly susceptible to ischemic and/or toxic injuries, which can affect the renal tubular function. Therefore, reliable and precocious markers of tubular dysfunction, such as RBPu, are useful in pediatrics. Methods: We studied healthy infants and children aged 1 month to 8 years, and healthy term and preterm babies without hemodynamic repercussion. We collected isolated urine samples once for children older than 1 month and periodically for those younger than that. Theses urine samples were used for the dipsticks test (Combur 9®, Boehringer), RBPu, and creatinine measurements. Results: We observed that the RBPu levels in children do not follow a regular distribution. After logarithm data transformation, we established an interval of reference for children older than 1 month: 3 to 269 μg/L, mean 27 μg/L. In newborns, we found a large variation of RBPu excretion. However, we noticed that the excretion decreases significantly, reaching the healthy adult levels at the end of the 1st month, for term as well as for preterm newborns. Conclusions: We suggest that RBPu can be used as a marker of proximal tubular dysfunction, since we were able to establish an interval of reference. Also, as this is not an invasive examination, it can be repeated whenever necessary during follow-up of this kind of injury. Moreover, this study contributes to the knowledge of the tubular function development, as it shows that at the end of the 1st month of life the newborn's kidney is as able to reabsorb RBPu as the healthy adult kidney is.

Methods

We studied healthy infants and children aged 1 month to 8 years, and healthy term and preterm babies without hemodynamic repercussion. We collected isolated urine samples once for children older than 1 month and periodically for those younger than that. Theses urine samples were used for the dipsticks test (Combur 9®, Boehringer), RBPu, and creatinine measurements. Results: We observed that the RBPu levels in children do not follow a regular distribution. After logarithm data transformation, we established an interval of reference for children older than 1 month: 3 to 269 μg/L, mean 27 μg/L. In newborns, we found a large variation of RBPu excretion. However, we noticed that the excretion decreases significantly, reaching the healthy adult levels at the end of the 1st month, for term as well as for preterm newborns. Conclusions: We suggest that RBPu can be used as a marker of proximal tubular dysfunction, since we were able to establish an interval of reference. Also, as this is not an invasive examination, it can be repeated whenever necessary during follow-up of this kind of injury. Moreover, this study contributes to the knowledge of the tubular function development, as it shows that at the end of the 1st month of life the newborn's kidney is as able to reabsorb RBPu as the healthy adult kidney is.

Results

We observed that the RBPu levels in children do not follow a regular distribution. After logarithm data transformation, we established an interval of reference for children older than 1 month: 3 to 269 μg/L, mean 27 μg/L. In newborns, we found a large variation of RBPu excretion. However, we noticed that the excretion decreases significantly, reaching the healthy adult levels at the end of the 1st month, for term as well as for preterm newborns. Conclusions: We suggest that RBPu can be used as a marker of proximal tubular dysfunction, since we were able to establish an interval of reference. Also, as this is not an invasive examination, it can be repeated whenever necessary during follow-up of this kind of injury. Moreover, this study contributes to the knowledge of the tubular function development, as it shows that at the end of the 1st month of life the newborn's kidney is as able to reabsorb RBPu as the healthy adult kidney is.

Conclusions

We suggest that RBPu can be used as a marker of proximal tubular dysfunction, since we were able to establish an interval of reference. Also, as this is not an invasive examination, it can be repeated whenever necessary during follow-up of this kind of injury. Moreover, this study contributes to the knowledge of the tubular function development, as it shows that at the end of the 1st month of life the newborn's kidney is as able to reabsorb RBPu as the healthy adult kidney is.

Resumen

Objetivo

O rim da criança, em particular o do recém-nascido, é especialmente susceptível a injúrias isquêmicas e/ou tóxicas, que comprometem preferencialmente os túbulos renais. Assim, marcadores precoces e fidedignos da função tubular renal seriam bastante úteis em Pediatria. A proteína transportadora de retinol urinária (RBPu) vem sendo utilizada com este propósito, funcionando como marcador de função do túbulo contornado proximal (TCP). Nesse sentido, nosso objetivo foi avaliar o comportamento da RBPu em crianças para estabelecer um padrão de referência e avaliar possíveis diferenças entre as diversas faixas etárias.

Métodos

Estudamos crianças normais, entre 1 mês de idade e 8 anos, e recém-nascidos normais, a termo (RNT) e pretermo (RNPT), estes últimos sem intercorrências além das inerentes à prematuridade, as quais não determinaram repercussões hemodinâmicas. Foram coletadas amostras isoladas de urina, sendo uma coleta para crianças acima de 1 mês e coletas periódicas abaixo desta idade. Nesta urina, além da realização de fita-teste (Combur 9®, Boehringer), procedemos à dosagem de RBP e creatinina.

Resultados

Observamos que os níveis de RBPu de crianças não seguem uma distribuição normal (resultados semelhantes aos da população adulta) e pudemos estabelecer um padrão de referência para crianças acima de 1 mês de idade, após transformação logarítmica dos dados, a saber, 3 a 269 μg/L, média geométrica 27 μg/L. Para as crianças até 30 dias de vida encontramos uma grande variação na excreção urinária de RBP. No entanto, notamos que essa excreção decresce significativamente para encontrar valores semelhantes aos de adultos normais no final do primeiro mês de vida, tanto para RNT como para RNPT.

Conclusões

Parece-nos bastante relevante utilizar a RBPu como marcador de função tubular proximal na infância, já que estabelecemos o intervalo de referência, lembrando que, sendo um exame não invasivo, poderá ser repetido periodicamente no seguimento desse tipo de injúria renal. Este estudo contribui também para o conhecimento do desenvolvimento da função tubular, mostrando que, com um mês de idade, o TCP é capaz de reabsorver a RBP como o rim de adultos normais.