Is my process doing always the same ?

Hello :)

I have a question. I wanna confirm or test if one of my process is doing what he has to do.
In this Process i analyzing how much value a certain marker from my material ( different cancer tissue) has. But i already know that in normal cases the material is not always the same. So my mean, can always be different. To compare the means would be pointless i think. So, can i only use the variance (like F-test) to compare if my process is doing always the same kind of measurement no matter what the source of the material is ?

Thanks for the help.