Which renal function test is most commonly used to assess glomerular filtration rate (GFR)?

The serum creatinine level is the most commonly used test to assess glomerular filtration rate (GFR) because creatinine is a byproduct of muscle metabolism that is produced at a relatively constant rate and is eliminated from the body solely through the kidneys. This makes serum creatinine a reliable indicator of the kidneys' filtering capability. When the GFR decreases, serum creatinine levels rise, providing clinicians with a clear and direct measure of renal function.

Additionally, serum creatinine is easy to determine through a routine blood test and is often included in standard metabolic panels. This widespread availability and the test's specificity to kidney function make it the preferred choice for estimating GFR, an essential indicator of kidney health and function.

In contrast, other tests such as blood urea nitrogen (BUN) can be influenced by factors unrelated to kidney function, such as protein intake and hydration status. Serum electrolytes provide information about the balance of minerals in the blood but do not specifically measure kidney function. A urine protein test helps identify kidney damage but does not provide a direct measurement of GFR. Thus, while these tests can play roles in assessing renal health, the serum creatinine level stands out as the primary and most effective means for evaluating GFR.