Which common test is performed to assess a patient's kidney function?

The blood urea nitrogen (BUN) test plays a critical role in assessing kidney function. This test measures the amount of urea nitrogen in the blood, which is a waste product formed from the breakdown of proteins. Under normal circumstances, healthy kidneys filter urea nitrogen from the blood and excrete it in urine. When kidney function is impaired, the levels of BUN can increase, indicating that the kidneys are not effectively removing this waste product.

In contrast, while a comprehensive metabolic panel does include BUN among other tests, its broader purpose is to evaluate overall metabolism, not exclusively renal function. Liver function tests focus specifically on liver health and do not provide direct information about kidney function, nor does the hemoglobin A1c test, which is used to monitor diabetes by measuring average blood glucose levels over time. Thus, the BUN test is specifically tailored to assess the efficiency and health of the kidneys, making it the most relevant choice for this question.