certified specialists are doctors who have advanced education, clinical training, and certification in a specific field. a sub-specialist is a doctor who is trained or certified as a specialist and then receives additional training in a specific area (sub-specialty).
a doctor becomes certified by completing training in a specialty area and passing an exam. to be certified, the doctor must complete the education required to get an md (medical doctor) or do (doctor of osteopathic medicine) degree, complete 3 to 7 years of training in a residency program in the specialty field, and pass a written test given by the royal college of physicians and surgeons of canada. many specialty boards also require doctors to pass an oral test.