Final answer:
A post BUN sample requires turning off the hemodialysis machine to accurately measure the urea nitrogen levels in the blood, indicating kidney function.
Step-by-step explanation:
To properly collect a post BUN (Blood Urea Nitrogen) sample, it is necessary to turn off the hemodialysis machine. This action is taken to ensure that the sample reflects the urea concentration in the blood after the kidneys have filtered it, without any further alteration by the dialysis process. BUN is a test that measures the amount of urea nitrogen in the blood, which is an important indicator of kidney function.