CO-198: Authorization units or days were exceeded

The payer is telling you the service was authorized, but you billed more days, units, or visits than they approved. Anything beyond the approved units is being cut to zero as not covered under the agreement. Mechanically, the claim line passes basic eligibility and benefit checks, then hits an authorization match edit. The system compares the billed date span and units to the approved start and end dates and allowed quantity, and writes off the overage as CO, not billable to the patient.

You see CO-198 a lot on per diem behavioral claims when length of stay goes past the last approved concurrent review. Example: PHP or IOP on a UB-04 where the UM nurse only extended 5 days, but billing sent 7 days without getting the extra authorization. It also shows up when a therapist keeps a patient in residential or detox for clinical reasons, but the concurrent review was only approved through a certain date and the team missed the next review window. The payer pays through the authorized discharge date and hits CO-198 on the remaining days. Carve-out behavioral vendors are strict on units too. Group codes (like 90853), family therapy, or telehealth visits with modifier 95 can hit CO-198 if the plan only authorized a fixed number of outpatient sessions or MAT visits and the clinic keeps seeing the patient without updating the auth.

• Pull the authorization record and UM notes to see the exact approved dates and units for that patient and level of care.
• Match the billed span and units by revenue code and CPT/HCPCS (per diem PHP/IOP, H0010/H0011 detox, H0018/H0019 residential, 90853, 90834, etc) to the authorization details to find the overage.
• If services were clinically continued but UM did not extend, work with clinical and UR staff to request a retro-authorization or post-service review following payer rules.
• If there is already an extended authorization that covers the denied units or days, correct the authorization number, span, or units on a corrected claim and resubmit electronically.
• If the payer refuses retro-authorization, adjust off the CO-198 balance as contractual and update your LOS or unit caps in the practice management system for that payer and level of care.
• For denials tied to telehealth or specific modifiers, confirm the authorization actually allowed telehealth and those codes, then correct modifiers or code selection and appeal with supporting UM records if appropriate.

• At admission and at each concurrent review, confirm payer-approved level of care, start and end dates, and approved units or days, and load them into your system.
• Build front-end edits that stop billing from submitting more days or units than are on the active authorization for each revenue code and CPT/HCPCS.
• Set UM and billing work queues with ticklers before auth end dates so PHP, IOP, residential, and detox reviews are completed and updated before billing passes the limit.
• For outpatient and telehealth, track authorized visit counts by provider and service type and prevent scheduling or billing beyond the remaining units without new authorization.