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CO-59 Denial Code: Multiple or Concurrent Procedure Rules

CO-59 means the payer reduced payment under multiple or concurrent procedure rules, such as multiple surgery, multiple diagnostic imaging, or concurrent anesthesia reductions. It's usually a pricing adjustment, not a denial, but it's worth checking the right procedure got full payment.

Quick facts

Code
CO-59 (CARC 59)
Status
Active In use since January 1, 1995; last modified July 1, 2017.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The standard group. The reduction is a contractual or policy adjustment the provider absorbs and can't bill to the patient.
Official description
Processed based on multiple or concurrent procedure rules. (For example multiple surgery or diagnostic imaging, concurrent anesthesia.) Usage: Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF), if present.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-59 means

CARC 59 says processed based on multiple or concurrent procedure rules. The official text gives examples: multiple surgery, multiple diagnostic imaging, and concurrent anesthesia. When several procedures are performed together, payers reduce payment for some of them because parts of the work (such as preparation or practice expense) overlap.

In a typical multiple surgery example, the procedure with the highest allowed amount is paid at the full rate and additional procedures are paid at a reduced percentage. Imaging and therapy have their own multiple procedure payment reduction (MPPR) rules under Medicare, and many commercial payers apply similar methods. The ERA shows the reduction as CO-59.

The usage note points to the 835 Healthcare Policy Identification segment for the payer’s policy.

Don’t confuse CARC 59 with modifier 59. The modifier marks a distinct procedural service; the CARC marks a payment reduction.

Common causes

  • Several surgical procedures in one session, billed with modifier 51 or ranked automatically by the payer.
  • Multiple imaging studies on the same day in contiguous body areas, under imaging MPPR.
  • Multiple therapy services in one day, under therapy MPPR rules.
  • Concurrent anesthesia where one anesthesiologist directs several cases at once.
  • Procedures ranked in the wrong order, so the higher-valued service is reduced.

How to check it

  1. Confirm the reduction applies. Were the procedures in the same session, and are they subject to reduction under the payer’s policy?
  2. Check which line got full payment. The highest-valued procedure should normally be paid in full.
  3. Look for exempt codes. Add-on codes and some other procedures are typically exempt from multiple procedure reductions.
  4. Compare the math to your contract and the payer’s percentages.
  5. If it’s right, post as a contractual adjustment. Don’t bill the patient.
  6. If it’s wrong, request reprocessing or reconsideration. If your modifiers or line order caused the problem (for example missing modifier 51, or separate sessions not identified with the proper modifier), send a corrected claim with resubmission code 7 in box 22.

How to prevent problems

  • List procedures in order of value on surgical claims.
  • Use modifiers correctly, including 51 where payers require it and appropriate modifiers for separate sessions.
  • Load multiple procedure rules into your expected payment calculations.
  • Monitor reductions over time. An ERA Analyzer can show CO-59 amounts by payer and code so incorrect reductions stand out.

Specialty notes

PT/OT practices see therapy MPPR reductions on almost every multi-service visit under Medicare. Radiology groups see imaging MPPR. Anesthesia groups see concurrency-related reductions when medically directing multiple rooms.

Remark codes that may appear with CO-59

  • N670 (This service code has been identified as the primary procedure code subject to the Medicare Multiple Procedure Payment Reduction (MPPR) rule.): This line was identified as the primary procedure under the Medicare Multiple Procedure Payment Reduction rule.
  • N936 (This service code has been identified as the secondary or tertiary procedure code subject to the Medicare Multiple Procedure Payment Reduction…): This line was treated as a secondary or tertiary procedure under the MPPR rule.
  • CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): Standard fee schedule reduction, often on the same line.
  • CO-97 (The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.): The service was bundled and not paid separately, rather than paid at a reduced rate.
  • CO-54 (Multiple physicians/assistants are not covered in this case.): Multiple physicians or assistants aren't covered for this case.
  • CO-236 (This procedure or procedure/modifier combination is not compatible with another procedure or procedure/modifier combination provided on the same day…): Procedure combinations that aren't compatible under NCCI or payer edits.

CO-59 FAQ

Is CO-59 a denial?

Usually not. It shows the payer paid a procedure at a reduced rate because it was performed with other procedures in the same session. Denials under bundling rules normally use other codes, such as CO-97.

How do multiple procedure reductions work?

Payers commonly pay the highest-valued procedure at 100% and reduce additional procedures by a set percentage under their policy. Imaging, therapy, and surgery each have their own rules, and details vary by payer.

Can CO-59 be wrong?

Yes. The reduction may be applied to the wrong procedure, to procedures exempt from reduction, or on services from separate sessions. Compare the payment to your contract and the payer's policy.

Is CARC 59 related to modifier 59?

No. CARC 59 is an adjustment reason code; modifier 59 is a procedure modifier indicating a distinct procedural service. They share a number but mean different things.