I have found the easiest way to understand this is to look at Appendix J in the CPT codebook.
The listing for sensory NCS of
Ulnar nerve to 4th digit and
Ulnar nerve to 5th digit would be considered to be two separate NCS studies.
Likewise sensory NCS of
Ulnar nerve to 4th digit and
Ulnar dorsal cutaneous sensory nerve would be considered to be two separate NCS studies. If performed bilaterally, these four NCS would be coded with 95908 x 1 unit of service.
For motor NCS, the "counting" is the same, in that
Median motor nerve to APB and
Median motor nerve to first lumbrical would be considered to be two separate NCS studies
Likewise motor NCS of
Ulnar motor nerve to ADM and
Ulnar motor nerve to FCR would be considered to be two separate NCS studies. If performed bilaterally, these four motor NCS would be reported with 95808 x 1 unit of service.
Testing of the motor NCS as well as the corresponding F-wave is only "counted" as one NCS. For example,
Median motor NCS to APB and
F-wave study of Median motor to APB would be considered to be a single NCS study, not two NCS.
Appendix J also provides a useful Table of Maximum Number of Studies that many payers incorporate into their coverage policies. The table establishes the reasonable maximum number of studies to arrive at the diagnosis listed in the left column in 90% of patients with that final diagnosis. For example, the reasonable maximum number of studies to diagnosis 90% of patients with bilateral carpal tunnel syndrome, would be 10 total NCS, whereas diagnosis unilateral CTS in 90% of the patients with that condition would require 7 NCS.
Payers and providers need to remember that the Maximum Number of Studies table only covers diagnosis of 90% of the patients with that condition, in that there remains 10% of those patients that may require more. The provider's documentation should indicate the medical necessity for additional studies beyond the Table's reasonable maximum.
Hope this makes more sense now! If not, let me know & we can discuss further!