In adult nephrology practice, proteinuria is assessed by measuring the amount of protein in a 24 hour urine collection.
Nephrotic range proteinuria is defined in adults as >3.5 g / 24 hours.
In children it is much harder to obtain complete 24 hour urine collections and we rely on measuring the protein / creatinine ratio in spot urine specimens. The amount of creatinine excreted each day is constant and proportional to muscle mass. Early morning urine specimens are collected to exclude orthostatic proteinuria.
Normal values are <20 mg protein / mmol creatinine.
Nephrotic range is >200 mg protein / mmol creatinine.