Mhy husband had his left kidney removed due to a solid mass which was found on a CT Scan. The reason they did the CT Scan was because he urinated blood. They didn't do a needle biopsy, but instead scheduled surgery ASAP. Good job they did, as it WAS a stage 1 malignant tumor which, due to it's early stage, hadn't spread anywhere else. I think the docs, through experience, can usually pretty well tell whether a mass is malignant or not (although it is also possible for a mass to be non-malignant too).
Whether or not they remove the kidney will, of course, depend on the needle biopsy that you're going to have, and the location of the mass. I say location, because depending on that, the docs will decide whether they have to remove the whole kidney, or whether they can do a partial. But don't worry. If you're not diabetic and have good blood pressure control, then your remaining kidney should be able to take on the work of both kidneys. Your doc will probably do lab work to check on your kidney function.
All the best. Keep us posted on your progress.