Answer: You can report nerve conduction studies (NCS, 95900-95904) for one of three types of nerves:
Motor NCS (95900 and 95903) describes stimulation at various points along a motor nerve containing motor fibers only. The physician records responses from a muscle innervated by those fibers. Codes 95900 and 95903 differ in that the latter includes F-wave recording, which includes additional stimulation to obtain more responses (at least 10).
Note: CPT no longer contains a code to describe recording of F-waves only.
Sensory NCS (95904) involves stimulation of sensory fibers only, with recording on a different site along the same nerve.
Sensory NCS can also involve stimulation of a nerve containing motor and sensory fibers while recording over an exclusively sensory branch of the same nerve. Which means that a Mixed NCS, which you should also bill using 95904, describes nerves containing both motor and sensory fibers.
In 2002, CPT eliminated the term "or mixed" from 95904's descriptor to avoid the misconception that 95904 bundled motor and sensory studies.
In other words, instead of reimbursing for one motor study (95900 or 95903) and one sensory study (95904), the insurer mistakenly paid for only a single "mixed" study (95904). A true mixed nerve conduction study, however, is separate and distinct from either sensory or motor studies.