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[Physiological proteinuria in the newborn]
Insights
Urinary protein levels in children, including albumin and immunoglobulin G, are highest at birth and change significantly in the first three months. Renal function and protein clearance mature rapidly during early infancy.
Area of Science:
- Pediatric Nephrology
- Clinical Chemistry
- Biomarker Discovery
Context:
- Investigating protein excretion in pediatric populations is crucial for understanding renal development.
- Laurell's electroimmunoassay provides a quantitative method for assessing specific protein levels in biological fluids.
Purpose:
- To quantify serum and urine levels of albumin, caeruloplasmin, immunoglobulin G, and alpha 2-macroglobulin in children aged 29 gestational weeks to 13 years.
- To characterize the developmental changes in renal protein handling and filtration selectivity during early life.
Summary:
- Urinary excretion of albumin, caeruloplasmin, immunoglobulin G, and alpha 2-macroglobulin is highest in newborns, decreasing with age.
- Serum/urine concentration ratios and protein clearances demonstrate significant maturation within the first three months of life.
- Gestational age did not influence initial urinary protein levels, but renal function and filtration selectivity develop rapidly postnatally.
Impact:
- Establishes normative data for urinary protein excretion in infants and children.
- Provides insights into the ontogeny of renal filtration and reabsorption processes.
- Highlights the dynamic changes in renal protein handling during the critical early developmental period.
Abstract:
The levels of the individual proteins albumin, caeruloplasmin, immunoglobulin G, and alpha 2-macroglobulin were determined by Laurell's electroimmunoassay in the serum and urine of 127 children. Their age ranged from 29 gestational weeks to 13 years. Highest levels of the proteins in the urine were found during the first days of life. The values did not depend on gestational age. The urine concentrations are influenced by glomerular filtration and the reabsorption of proteins and water. The steady state of these functions can be characterized by the serum/urine concentration ratios and the clearance of the proteins. In the first days after birth the permeability of the renal barrier is maximal, the concentration ratios are low and increase markedly up to the end of the first three months; after that, they continue to rise only slightly. The clearances of all the examined individual proteins decrease between term and the third month of life, thereafter increasing until late childhood. The selectivity of the glomerular filtration also shows its highest rate of development during the first days after term.