Qualifications
Where to start? Long list. Okay, deep breath, here we go. You'll need an undergraduate degree (pre-med, of course), a medical degree, three years of residency in internal medicine, another three years as a nephrology fellow, a couple years of research experience, and board certification. Phew.
In addition to the very time-consuming qualifications, you'll have to satisfy a number of more abstract qualities in order to do well in this career. You'll need to be willing to sacrifice your own time and well-being for the sake of others. You'll need a really good memory (and/or a really organized method of note-taking). You'll also need a creative approach to problem-solving, as not every issue will be obvious or easily taken care of.