Which laboratory value is primarily used to assess kidney function?

Serum creatinine is a key laboratory value used to assess kidney function because it is a waste product generated from muscle metabolism and is typically produced at a relatively constant rate. The kidneys filter creatinine out of the blood and excrete it in the urine, making it a reliable indicator of kidney performance. When kidney function declines, serum creatinine levels tend to rise because the ability of the kidneys to effectively filter and excrete waste products decreases.

While blood urea nitrogen (BUN) is also used in assessing kidney function, it is influenced by factors other than kidney function, such as protein intake, liver function, and hydration status, which can complicate its interpretation. A complete blood count (CBC) focuses on components like red and white blood cells and platelets, and does not provide direct measurements of kidney function. An electrolyte panel measures levels of various ions, which can give information about various bodily functions, including kidney activity, but it is not the primary test for assessing kidney function itself. Therefore, serum creatinine is considered the most direct and relevant marker among these options for evaluating kidney health.