What is the best identifier of infant kidney function?

Serum creatinine is the best identifier of infant kidney function because it provides a reliable measure of kidney filtration capacity. In infants, serum creatinine levels reflect glomerular filtration rate (GFR), which is an important indicator of renal function. Unlike blood urea nitrogen, which can be influenced by factors such as hydration status and protein intake, serum creatinine is a more constant measure that directly correlates to the kidneys' ability to filter waste from the bloodstream.

Measuring urine output is also important in assessing kidney function, but it can be variable and influenced by fluid intake, making it less reliable as a singular indicator. Electrolyte levels can indicate kidney function, but they are also affected by a range of other physiological processes, so they are not as definitive for assessing overall kidney health as serum creatinine is. Thus, serum creatinine stands out as the most accurate and useful parameter for evaluating renal function in infants.