Which is considered more specific for kidney failure, creatinine or BUN?

Creatinine is considered more specific for kidney failure than blood urea nitrogen (BUN) due to its clearer association with renal function. Creatinine is a byproduct of muscle metabolism and is produced at a relatively constant rate. It is filtered out of the blood by the kidneys, so an increase in creatinine levels directly indicates impaired kidney function. This makes it a reliable marker for kidney health.

BUN, on the other hand, can be influenced by various factors other than kidney function, such as hydration status, dietary protein intake, liver function, and gastrointestinal bleeding. Therefore, while BUN can provide useful information regarding overall health and may indicate kidney involvement in some cases, it is less specific than creatinine for diagnosing kidney failure.

In summary, creatinine is favored as a more specific indicator of kidney function because it reflects the kidneys' ability to filter waste products from the blood, with minimal interference from non-renal factors.