There are three different code categories, Category I, II, and III. The first category I codes are the most numerous and each are five digits long all numeric. Each of them has a description of the procedure the code is for. For example 99204 is Officer or other outpatient visit for evaluation and management of a new patient. They are grouped into sections, but they can be used by any physician. For instance a regular physician may use a surgical code even though he is not a surgeon. Each of these codes are for procedures that are known working procedures. So chemotherapy is a known working procedure it would fall under category I, but a procedure that they are still testing for effectiveness would not be in this category.
Category II codes are used to track performance measures for medical goes. For instance, when a patient comes in to lose weight or to quit smoking, then the category II code comes into use. Each of these codes has an alphabetic character as the last digit. Category III codes are used for temporary technology, services, and procedures, but if they are proven effective then it can turn into a permanent code. So these codes are only used for experimental procedures. When a new procedure is introduced, but not yet proven effective then it is assigned a temporary code. If the procedure is proven affective then it can switch and become a permanent code, and these also have an alphabetic character for the last digit. So an easy way to remember these categories would be: Category I: All working( procedures done in an office that are proven working procedures) Category II: Medical Goals (such as weight loss, or stop smoking) Category III: Temporary (still being tested)