News items Research sets standard for renal function of newborn babies

28 April 2022

Researchers at Radboud university medical center have succeeded in establishing reference values for functioning of the kidneys of newborn babies. This allows for earlier detection of kidney injury and for improved dosing of drugs handled by the kidneys. Until now there had been little common knowledge about kidney function during the first month of life, making it difficult for physicians to know the kidney status. Now there is better information.

Our kidneys maintain the fluid and salt balance in our bodies by filtering the blood and excreting waste products in the urine. How well kidneys work is measured by the amount of blood that the kidneys filter per minute. This is called the glomerular filtration rate (GFR) and is often determined from the clearance of the waste substance creatinine. A lower amount of creatinine in the blood indicates better kidney function. For adults and older children, the filtration rate of healthy kidneys has long been known, but the data were not so good for newborn term babies. It was clear that kidney function improves in the first month after birth but the details were not so well known.

Making an accurate estimate is now much easier, thanks to this new publication led by researcher Nori Smeets, and colleagues. She examined the kidney function of almost a thousand healthy babies from fifty international studies and combined all these data into an age-based measure of kidney function during the first month of life. There was a large increase in kidney function during the first week, such that GFR doubled in the first five days after birth. After that, it is known kidney function continues to rise gradually during the first month of life. 

Tested in practice

To properly estimate the kidney function of babies during hospitalization, Smeets and the researchers proposed a new GFR estimating equation by using the length of the baby and its serum creatinine. The calculation was tested in a group of almost fifty babies admitted to Radboud university medical center. This proved that the proposed equation works very well. Smeets: 'I am pleased that we have been able to demonstrate that our equation is accurate. As far as we're concerned, this lays the foundation for estimating kidney function of term and preterm infants during the first year of life.

Better dosage of medication

Because we now have a much better understanding of how kidney function develops in term newborns, we can better dose medications that are handled by the kidneys. The kidneys play an important role in the excretion and secretion of medications. Smeets: 'Now that we know how  kidney function develops in the first month of life, doctors can prescribe much more appropriate dosages of medications handled by the kidneys. This varies from day to day in that first month, our research shows.’ 

In addition, it is now possible to better detect kidney failure, Nori Smeets explains. 'In Radboud university medical center we are going to ensure that the kidney function is automatically displayed in the patient file. This way we can see whether a child admitted to our hospital may have kidney problems. If we see that the kidney function is lagging behind, we can adjust the dosage of medication and make sure that these children have a reduced chance of injuring their kidneys. We keep a better eye on our babies.' 

The goal of Smeets and colleagues at the departments of Pharmacology and Toxicology and Paediatric Nephrology at Radboudumc Amalia Children's Hospital is to further disseminate this information. Smeets: 'For the first time, there is a standard to estimate kidney function of newborn babies. The more this standard is used, the better we can treat babies and prevent kidney injury.’

About the publication

This article was published in Journal of the American Society of Nephrology: Maturation of glomerular filtration rate in term-born neonates: an individual participant data meta-analysis – Nori J.L. Smeets, Joanna IntHout, Maurice J.P. van der Burgh, George J. Schwartz, Michiel F. Schreuder, Saskia N. de Wildt. DOI: 10.1681/ASN.2021101326.

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