As long as you or your spouse is working for that private insurance, you DO NOT need to take Medicare Part B. However, Part B is what covers the transplant drugs post transplant. So at that point you may want to look into it depending on the drug coverage on your current plan. There is no penalty for not taking Part B - for starters you have ESRD so you can enroll at any time, and second, because you have private health insurance, you get a special enrollment period when that insurance ends or the work stops. Why do you *have* to take Part A??
Cariad - the 10% per year penalty really only ever applies to people who are 65 or on disability (not on Medicare for ESRD) that get penalized. The enrollment period for people on ESRD is very different. I can site all the policy and try to explain it if anyone is really interested... it's interesting, and can be confusing. The one explains how to figure out when it might be best to enroll in A and B https://secure.ssa.gov/apps10/poms.nsf/lnx/0600801251#b