What is considered the best indicator of Glomerular Filtration Rate (GFR)?

The best indicator of Glomerular Filtration Rate (GFR) is urine creatinine clearance. This measurement reflects the kidney's ability to filter creatinine from the blood, making it a direct estimate of GFR. The process involves collecting urine over a 24-hour period and measuring the amount of creatinine excreted, along with the serum creatinine level. By assessing both urine and plasma creatinine concentrations, the creatinine clearance calculation provides a more accurate representation of kidney function compared to other markers.

While blood urea nitrogen and plasma creatinine levels can indicate kidney function, they are influenced by several factors, including hydration status, protein intake, and muscle mass, making them less reliable than urine creatinine clearance. Similarly, a 24-hour urine protein measurement primarily assesses proteinuria rather than directly estimating GFR, so it is not the preferred indicator for evaluating renal filtration capacity. The urine creatinine clearance method is favored in clinical practice to assess renal function accurately.