CPT® code 99318 is used to bill an annual nursing facility assessment.  It requires three of three of these components:  a detailed interval history, a comprehensive exam, and low or moderate medical decision making.

This visit is payable once per year for a resident in a nursing facility. 

It may be used as one of the mandated nursing facility visits.  Medicare does not expect a provider to bill this service in addition to a mandated, subsequent nursing facility visit when the annual assessment is performed at the time of the mandated visit.  Here is what the Medicare manual says about this:

Beginning January 1, 2006, the new CPT® code, Other Nursing Facility Service (99318),
may be used to report an annual nursing facility assessment visit on the required schedule
of visits on an annual basis. For Medicare Part B payment policy, an annual nursing
facility assessment visit code may substitute as meeting one of the federally mandated
physician visits if the code requirements for CPT® code 99318 are fully met and in lieu of
reporting a Subsequent Nursing Facility Care, per day, service (codes 99307 – 99310).  It
shall not be performed in addition to the required number of federally mandated
physician visits.  The new CPT® annual assessment code does not represent a new benefit
service for Medicare Part B physician services. 
 

The service may be performed by either an MD or a qualified Non-Physician Practitioner (NPP), but may not be billed as a shared service or incident to service.