Can I be terminated due to a medical condition?

They may be able to terminate you. Under anti-discrimination laws, businesses must make "reasonable" accomodations for "disabilities." Let's assume that kidney disease would be considered a disability. Then the question is, what is reasonable? For a small company to continue to employee someone with frequent absences may not be reasonable.

You should consult with an employment attorney with whom you can share all the details of your situation in confidence. You should prepare for the meeting by thinking about what accomodations you could make and suggest that your employer make that will make this a winning situation. Can you do some work offsite, while undergoing medical care? You could suggest that. Could you do most of your job, so you're still valuable to them, but maybe accept and live with a pay cut, to make you more affordable or more of a bargain? Etc.--try to be creative in making the situation work for both of you.