CO-151: The units or frequency billed exceed what the documentation or the payer's edits support

Group CO means contractual obligation: the balance is written off, not billed to the patient. The number is the reason; the two-letter group says who carries the balance.

Remark codes that usually come with CO-151

Common causes

How to fix it and resubmit

1. 1

   Check the units against the code definition and the edit

   Confirm how the code is counted (per timed unit, per session, per item, per dose unit) and look up the published MUE value or the payer's frequency policy for the date of service. Confidential MUE values will not be on the list; the payer can tell you the edit fired without telling you the number.

2. 2

   Corrected claim when the count was keyed wrong

   Convert minutes to units, packages to HCPCS units, or two lines to one with modifier 50 as the payer requires, and resubmit with frequency code 7. Fix the charge entry rule that created the error so it does not recur next week.

3. 3

   Separate lines with modifiers when the units are real

   Where the services on one date were distinct and the payer's edit is per line, report them on separate lines with the modifier that explains them (59 or an X modifier, 76, 91 as the case fits), with the documentation ready. Where the edit is per date, this does not help and the route is an appeal.

4. 4

   Appeal with the time log and the order

   When the units are accurate and the record shows them, appeal with the note, the start and stop times or procedure count, the order and a short statement of why this patient needed that many. Payers decide these on the documentation, so send all of it the first time.

5. 5

   Treat a benefit limit as a benefit limit

   If the payer's frequency rule is a plan limit rather than a coding edit, the claim is a CO-119 problem: confirm the accumulator and decide who owes the balance.

How to prevent it

• Units validation in the scrubber against the published MUE table and each payer's frequency policies, refreshed when CMS posts the quarterly files
• Charge entry rules that convert minutes to units for timed codes and package counts to HCPCS units for drugs and supplies
• Bilateral and repeat-service rules per payer, so modifier 50, 76 or 91 and the unit count match what the payer's edit expects
• Documentation templates that capture start and stop times or a procedure count for every timed or multi-unit code

Official text: the X12 claim adjustment reason code list. The meaning above is our paraphrase for billers; the list is the authority.