CO-199 is a facility claim denial. The revenue code on a line says one thing, and the CPT or HCPCS code says another. Payers keep tables of which procedure codes can go with which revenue codes. When a line pairs, for example, an MRI code with a plain X-ray revenue code, the edit fails. It almost always traces back to the hospital’s charge master. (Primary source: X12 Claim Adjustment Reason Codes)
In brief: CARC 199 reads “Revenue code and Procedure code do not match.” Look at FL 42 and FL 44 on the denied line. Find the revenue code that fits the service, fix the charge master entry, and send a replacement claim (type of bill frequency 7).
Part of our denial codes library. Written by Manikandan J, CPC, CRCR, who has reviewed hospital charge masters for revenue code accuracy. Published 22 October 2026. Last updated: 22 October 2026. Code wording quoted word for word from X12.
Official CARC 199 description
| Field | X12 text |
|---|---|
| Code | 199 |
| Description | “Revenue code and Procedure code do not match.” |
| Start | 10/31/2006 |
Source: X12 Claim Adjustment Reason Codes, checked 22 October 2026.
Revenue codes in plain terms
A revenue code is the four-digit code in UB-04 FL 42 that tells the payer which hospital department or type of charge a line belongs to. The NUBC maintains them. The procedure code in FL 44 is the CPT or HCPCS code for the exact service. The charge master is the hospital’s master list that links each charge to both codes. Because the CMS-1500 has no revenue code field, CO-199 only happens on institutional claims. See NUBC for the official code list.
| Revenue code | Department | Typical procedure codes |
|---|---|---|
| 0320 | Diagnostic X-ray, general | Plain X-rays such as 71046 |
| 0350 | CT scan, general | CT codes such as 70450 |
| 0610 | MRI, general | MRI codes |
| 0611 | MRI, brain and brainstem | 70551-70553 |
| 0636 | Drugs requiring detailed coding | J-codes with units |
Example scenario (fictional names), part 1
CO-199 Denial Example: What Happened
Nadia Hussain works in patient financial services at Lakeview Regional Hospital. Dr. Paul Grant, a neurologist, ordered an MRI of the brain without contrast (70551) for a patient with a headache (R51.9). The outpatient claim went to Clearwater Health Plan, a fictional commercial plan, with revenue code 0320 on the MRI line.
The 835 showed CAS*CO*199 on that line with remark LQ*HE*M50, “Missing/incomplete/invalid revenue code(s).”
How did an MRI end up billed under the X-ray department? Keep reading, or jump to how the CO-199 denial was resolved.
Why payers deny with reason code 199
- Charge master mapping errors. For example, a new imaging code was added under the wrong department code.
- Department moves. A service moved to a new department, but the charge still posts to the old revenue code.
- Drug lines under the wrong code. J-codes billed under a general pharmacy revenue code when the payer wants 0636.
- Payer-specific rules. Some payers require more specific subcategory codes, such as 0611 for a brain MRI.
How to fix a CO-199 denial
- Read the denied line. Note the revenue code in FL 42 and the procedure code in FL 44.
- Find the right pairing. Use the NUBC list, the payer’s billing guide and the CMS outpatient claims manual for Medicare rules.
- Check the charge master. Find the entry that produced the line and correct its revenue code.
- Look for other claims. Run a report for the same charge code to find other denied or pending claims.
- Send a replacement claim. Use type of bill frequency 7 in FL 4 (for example 0137) and the original claim number in FL 64.
Example scenario (fictional names), part 2
How the CO-199 Denial Was Resolved
What Nadia found: the brain MRI charge had been added during a scanner upgrade and copied from an old X-ray entry. It kept revenue code 0320.
The fix:
- She asked the charge master team to change the entry to 0611 (MRI, brain and brainstem).
- She sent a replacement claim, type of bill 0137, with 0611 in FL 42 and the original claim number in FL 64.
- 70551 in FL 44 and R51.9 in FL 67 stayed the same.
Outcome: Clearwater paid the MRI line. The report turned up nine other MRI claims with the same mapping, and Nadia corrected them all.
Names and details are illustrative; no real patient data.
CMS-1500 not shown: revenue codes exist only on the institutional claim (FL 42), so this denial can't occur on a CMS-1500.
- FL 42: revenue code 0320 (diagnostic X-ray) changed to 0611 (MRI, brain and brainstem) to match 70551.
- FL 4 + FL 64: type of bill 0137 (replacement) with the original claim number.
- FL 44 / FL 67: 70551 and R51.9 (entered as R519) are unchanged.
- CMS-1500: no equivalent box; revenue codes are institutional only.
CO-199 vs related codes
| Code | What it says | Key difference |
|---|---|---|
| CO-199 | Revenue code and procedure code don’t match | Pairing problem on a facility claim |
| CO-16 | Claim lacks information | Missing data |
| CO-181 | Procedure code invalid on the date of service | Code itself is invalid |
| CO-189 | Unlisted code billed when a specific code exists | Wrong code choice |
Prevention checklist
- Review every new charge master entry for the right revenue code before it goes live.
- Run a quarterly report that pairs revenue codes with procedure codes and flags odd matches.
- Keep payer-specific revenue code rules in the billing system.
- Retrain staff when departments move or new equipment adds codes.
Recap
CO-199 means the revenue code and the procedure code on a facility line don’t match. Fix the revenue code in FL 42, correct the charge master entry and send a replacement claim with type of bill frequency 7. Then search for other claims built from the same entry.
FAQ
What does CO-199 mean?
The payer says the revenue code and the procedure code on the line don’t match.
Can CO-199 happen on a CMS-1500?
No. The CMS-1500 has no revenue code field. CO-199 is an institutional (UB-04 or 837I) denial.
Which revenue code goes with a brain MRI?
Revenue code 0611 (MRI, brain and brainstem) is the specific choice. Some payers also accept 0610.
How do I resubmit a corrected facility claim?
Use frequency 7 as the last digit of the type of bill in FL 4, such as 0137, and put the original claim number in FL 64.
Can the hospital bill the patient for a CO-199 line?
No. Group code CO keeps the amount with the provider.
Sources
How we checked: each code quote on this page was matched word for word with the X12 CARC and RARC lists on 22 October 2026.
- X12, Claim Adjustment Reason Codes (CARC 199, 16, 181, 189). Accessed 22 Oct 2026.
- X12, Remittance Advice Remark Codes (M50). Accessed 22 Oct 2026.
- NUBC, UB-04 data specifications. Accessed 22 Oct 2026.
- CMS, Medicare Claims Processing Manual, Chapter 4. Accessed 22 Oct 2026.
- CMS, Medicare Claims Processing Manual, Chapter 25 (UB-04 completion). Accessed 22 Oct 2026.
Last updated: 22 October 2026 · Educational content; not legal advice.