Urgent care billing is very similar to family practice or internal medicine billing. (Of course without the routine physical codes.) The difference is the patients don't have appointments, they just walk in. There shouldn't be any special codes. The after hours code or weekend codes don't apply since that is during regular hours for the urgent care. They will mostly use the E&M codes for the visits, with some possible strep tests, urinalysis, ekg possibly, etc.
Michele