Urgent Care vs ER
Addressing the first question on charging patients an urgent care copay but possibly billing an ER visit, I would call the insurance company and talk with a rep and ask how the claim was billed. Primarily we need to know what place of service was billed since that determines how the benefits are applied. If they billed place of service 20 or 22 then your urgent care copay should have applied correctly, but if they billed a 23 then the ER copay/deductible-coins should apply and you would know then that it was billed incorrectly as you were not told that they were going to bill this way. Then you could contact the billing agency and ask them why they submitted a claim to the insurance company with the incorrect place of service.
For the second question on patients with no appointments to bill as urgent care - This is what I found regarding that.
CPT Assistant August 2010 addresses After Hours Office Services (Codes 99050-99051)
Let the Clock Determine 99050 vs. 99051 (AMA source)
If your physician sees a patient in the office during hours when the practice would normally be closed, such as on weekends or after 6 p.m., CPT guidelines allow you to bill 99050 (Services provided in the office at times other than regularly scheduled office hours, or days when the office is normally closed [e.g., holidays, Saturday or Sunday], in addition to basic service) as long as the documentation supports the afterhours service, says Jetton Torix, CCS-P, CPC-H, course director of Knowledge Source Seminars in Star, Idaho.
Keep in mind: A patient is considered an after-hours patient only if he reports to the office after your normal office hour's end — not when he presents during normal office hours and the appointment runs past closing time.
When your physician provides an E/M service in the office during regularly scheduled “evening, weekend, or holiday office hours,” by contrast, you should bill 99051 (Service provided in the office during regularly scheduled evening, weekend, or holiday office hours, in addition to basic service), according to AMA guidelines outlined in the CPT Assistant (Vol. 13, Issue 6, June 2003).