Aso, what other services were billed on the claim? For example, they will deny 95900 if you also billed a 95903; you would then need to check the report to determine if those studies were different nerves, and could use a 59 modifier if so. Also, as the previous responder noted, check your local carrier/MAC for an LCD. One carrier, WPS, has in their LCD that an NCS performed without EMG is screening and therefore not covered.
Hope this helps,