First of all, the authorizing bodies of CMA and RMA are different from each other. CMA is awarded by American Association of Medical Assistants while RMA is bestowed by the American Medical Technologists.
Many states of U.S.A. like Southern California have certain reservations that force them to accept only those medical assistants who have obtained CMA certification.
While there are many other states that do not only accept CMA but also allow practice to the medical assistants who have obtained RMA certification.
Besides U.S.A. both certifications CMA and RMA are recognised in all major countries of the world because the basic functionality of these two certifications is almost the same.
In some states of America, if you have a CMA certification, you are still not qualified enough to become a medical assistant replacing a full time nurse and for that purpose you need to obtain a certification of Certified Nursing Assistant (CNA).
On the other hand, if you have RMA certification then these states usually allow you to work as a nurse. But still there are many medical institutes that require CNA for those who want to practice as a full time nurse of medical assistants.
The major qualification required for obtaining CMA certification is that you have to be a graduate from a recognised institute from CAAHEP or ABHES. Besides that, for getting certification pass the exam of CMA.
For RMA certification, which is awarded by American Medical Technologists, the same qualification is required which is that you should be a graduate and that you also need to have five years’ experience of working as a medical assistant and then pass the final exam of RMA.