There is a vast difference in the scope of practice between these health care providers.
1. CNA= certified nurse aide/assistant. It depends on the program you go to, but I believe you must have a high school diploma. I am not certain of the length of the program anymore but it is no more than 6 months. You are qualified (after a competency exam given either by your program or the state agency) to give bed baths, make beds, give physical care (assist out of bed to chair, chair to toilet, assist to ambulate iow walk, do passive range of motion exercise), take vital signs, weigh and measure patients and other such things as is outlined in your scope of practice from your employer and the state from pediatrics to geriatrics. Many CNA's are employed in hospitals, nursing homes/rehab centers, and as home care attendants.
2. LPN= licensed practical nurse. Has at least 1 year of education devoted to patient care, pathophysiology, basic nutrition, and care of the psychiatric/geriatric/medical/surgical/obstetric
/pediatric patient, basic pharmacology and medication dosage and calculation and medication administration, and basic education on the scope of practice of the licensed practical nurse including the legal implications of actions.
3. RN=registered nurse. There are different pathways to becoming an RN.
a. diploma school. There are very few, if any of these schools remaining in the U.S. They are usually affiliated with a hospital and almost from day 1 you are on the hospital floors caring for patients. Classroom work is interspersed with your clinical training. You work shifts and complete training in 3 years.
b. associate degree. Usually at a 2 year community or junior college. Students are required to take anatomy and physiology, microbiology, math, various courses in psychology, in addition to liberal arts (English, foreign language, sociology) and take nursing courses right along with those.
c. BSN= bachelor of science in nursing. This is a 4 year degree program where your liberal arts courses and program prerequisites are taken in the first 2 years of the program and the last 2 years are devoted to the nursing curriculum.
Now I am not sure if when you wrote CNA you meant CRNA, which is totally different (that is a certified registered nurse anesthetist, which requires a 4 year nursing degree, at least 2 years of critical care nursing experience in a hospital setting, then 24-36 months more of school on a Master's degree level to complete) or what I have listed above. Please realize that I went through all of the training listed, I was a CNA, an LPN, got an assoc. degree, then BSN but this was in the 80's so requirements may have changed but basically this is what is taught at each level (I taught the CNA's and LPN's in the 90's). Hope this helps. Sorry for the length.