CO-151 Denial Code: Frequency or Units of Service Not Supported

CO-151 is a Claim Adjustment Reason Code that means the payer adjusted (or denied) payment because the information on the claim does not support the number or frequency of services billed. On Medicare DME claims it often pairs with remark code N115 when an LCD sets the frequency limit. (Primary sources: X12 Claim Adjustment Reason Codes · Noridian JA DME, Reason Code 151 | Remark Code N115 · CMS Medically Unlikely Edit (MUE)s)

Quick answer: CO-151 means the plan says the claim doesn’t support this many services or this frequency. Review the LCD or policy frequency limit, the MUE unit max, prior paid claims and date spans. Fix overlapping dates with a reopening when allowed, reduce units if supplier-liable, or appeal with documentation that supports medical need.

Part of our denial codes library. Written by Manikandan, a revenue cycle management specialist with more than 10 years of US medical billing experience. Last reviewed: 9 October 2026. Official code wording is quoted word for word from X12; Medicare rules link to their CMS or Medicare contractor source.

CO-151 denial code description (official X12 wording)

X12 Claim Adjustment Reason Code 151, verbatim:

“Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.”

Source: X12 Claim Adjustment Reason Codes, checked 9 October 2026. Start: 10/31/2002 | Last Modified: 01/27/2008.

CARC 151 was split out of the older code 57 (Stop: 06/30/2007), which covered level of service, quantity, length, dosage and day’s supply in one line. Today 150–154 each cover one of those ideas. The phrase that matters here is this many/frequency of services.

What CO-151 means in plain English

Each part of the code answers a different question:

• CO (Contractual Obligation) is the payer’s classification of who carries the amount. CMS says these adjustments are “Generally… considered a write off for the provider and are not billed to the patient” (Medicare Claims Processing Manual, Ch. 22, §60.1).
• CARC 151 tells you why: the payer does not agree that the documentation or claim data supports the units or how often the service was billed.

Typical triggers include, for example, an LCD frequency ceiling. Other common causes are overlapping DME date spans, same-or-similar equipment already on file, units above an MUE, or a plan visit limit.

In plain terms: the payer says you billed too many units or too often. Check the frequency rule, then fix units or appeal with proof.

CO-151 vs CO-150, CO-152, CO-119 and CO-50

Code	Official X12 text	What it tells you
151	“Payment adjusted because the payer deems the information submitted does not support this many/frequency of services.”	Units or frequency aren’t supported
150	“Payer deems the information submitted does not support this level of service.”	Level of service (for example E/M intensity), not quantity
152	“Payer deems the information submitted does not support this length of service.”	Length of service, not how many times
119	“Benefit maximum for this time period or occurrence has been reached.”	A hard benefit max was hit (different from “documentation doesn’t support”)
50	“These are non-covered services because this is not deemed a ‘medical necessity’ by the payer.”	Medical necessity denial. See CO-50

When the payer is objecting to how many or how often, look for 151. When it is objecting to medical necessity as a whole, look for 50 (often with N115).

CO-151 vs PR-151 vs OA-151 vs PI-151

CARC 151 can come with any group code, and payers don’t all use the same one:

Group + 151	Who carries the amount	Can you bill the patient?	When you’ll typically see it
CO-151	Provider	No, unless a valid ABN shifts liability	Common on Medicare DME and commercial remits
PR-151	Patient	Only after you confirm patient liability (for example a signed ABN)	Some remits when the patient was notified
OA-151	Neither group fits	Check the remark codes	Used “when no other group code applies” (CMS Ch. 22, §60.1)
PI-151	Payer-initiated reduction	No	Non-Medicare remits only. CMS lists just CO, OA and PR as valid on Medicare remittances

Don’t bill the patient for a CO-151 until you’ve ruled out a billing or documentation fix and confirmed that an ABN (or plan equivalent) actually shifts liability.

Remark codes that help with CARC 151

Noridian JA/JD DME publishes Reason Code 151 with remark code N115 when the decision rests on an LCD:

RARC	Official X12 text	What it adds
N115	“This decision was based on a Local Coverage Determination (LCD) (LCD). An LCD provides a guide to assist in determining whether a particular item or service is covered. A copy of this policy is available at www.cms.gov/mcd, or if you do not have web access, you may contact the contractor to request a copy of the LCD.”	The frequency or coverage limit comes from an LCD
N130	“Consult plan benefit documents/guidelines for information about restrictions for this service.”	Plan documents set the restriction (often commercial)
M80	“Not covered when performed during the same session/date as a previously processed service for the patient.”	Same-day overlap with a prior paid service

RARC wording is quoted from the X12 RARC list, checked 9 October 2026. Always open the LCD or policy article named by the MAC before you appeal.

Where CO-151 shows up in the 835

Here’s a trimmed, illustrative example for a DME supply line billed with 4 units:

CLP*PT20261001A*1*480.00*120.00*360.00*MB*2626000987654~
SVC*HC:A4253*480.00*120.00**4~
CAS*CO*151*360.00~
LQ*HE*N115~

• SVC shows HCPCS A4253 with 4 units billed.
• CAS*CO*151*360.00 is the group code, reason code and adjusted amount for the unsupported units.
• LQ*HE*N115 points to an LCD-based decision.

This 835 snippet is illustrative only.

How to fix CO-151: decision path

1. Read every remark code. If you see N115, open the LCD and policy article for that HCPCS. Noridian lists “Policy frequency limits may have been reached, per LCD” and “date span overlap or overutilization based on related LCD” as common reasons (Noridian JA DME, 151 | N115).
2. Check prior claims and date spans. Overlapping rental or supply periods are a frequent DME trigger. Noridian: “To avoid overlap, review previous claim submissions and date spans.”
3. Check the MUE. CMS publishes Medically Unlikely Edit (MUE)s for the “maximum units of service… under most circumstances for a single beneficiary on a single date of service” (CMS MUE). Compare billed units to the MUE and to the LCD frequency.
4. Same or similar equipment? For DME, use the Noridian Medicare Portal Same or Similar options (or the IVR) before you dispense.
5. Date-span clerical fix? Noridian allows a portal reopening in the portal “To adjust date span based on medical records available to supplier.”
6. Medical need above the usual limit? Submit a redetermination appeal with supporting documentation. Noridian encourages portal appeals and says to review the LCD, policy article and Documentation Checklists first.
7. Supplier liable vs patient liable. If you knew the frequency wouldn’t be covered, an ABN may have been required. Without a valid ABN, don’t bill the Medicare patient for a CO write-off.

Medicare and major payer notes

Noridian JA and JD DME both publish Reason Code 151 alone and paired with N115. Common causes on the 151 page include same-or-similar equipment and date-span overlap. On the N115 pairing page they add LCD frequency limits and point suppliers to the MUE tool, portal reopenings for date-span fixes, and redetermination appeals when medical need must be shown (Noridian JA 151, 151 | N115, JD DME 151 | N115).

MUE vs LCD. An MUE is a unit edit for one date of service. An LCD frequency limit can span days, months or a certification period. Hitting either can surface as CO-151 (or a related code). Check both.

Commercial plans. Many plans use visit or unit caps in prior-auth review. The same CARC 151 wording applies; the accompanying RARC (often N130) and the plan’s medical policy tell you which limit was applied.

Worked example (illustrative)

A DME supplier bills four boxes of diabetic test strips (A4253) for a period that overlaps a prior paid span by 10 days. The remit returns CAS*CO*151 with N115.

Reading it: the LCD frequency and the overlapping dates are the problem, not medical necessity of diabetes testing in general.

Fix: reopen in the Noridian portal to correct the date span to the non-overlapping days, or reduce units to the LCD-supported quantity. If usage above the usual limit is medically necessary, appeal with the physician order, testing log and LCD checklist.

Prevention: check Same or Similar and prior paid spans before shipping, and set claim edits for the LCD frequency.

CO-151 appeal / reopening template

Use this when you need a date-span reopening or a redetermination appeal for medical need above the usual frequency. Replace the bracketed text.

[Date]
[MAC / payer] Appeals / Reopening
[Address, fax or portal reference]

Re: CO-151 (frequency/units not supported) — [reopening / redetermination]
Patient: [Name]   MBI / Member ID: [ID]   DOB: [MM/DD/YYYY]
Claim number: [Claim #]   Date(s) of service: [MM/DD/YYYY]
HCPCS / CPT: [Code]   Units billed: [N]   NPI: [NPI]

The remittance shows CAS*CO*151 with remark [N115 / other]. Please:
[ ] Reopen to correct the date span to [corrected span] per the enclosed
    delivery ticket / order (clerical date-span fix).
[ ] Redetermine medical need for [units / frequency] under LCD [LCD #]
    and the enclosed clinical documentation.
[ ] Confirm the applicable MUE and LCD frequency we should use going
    forward.

Enclosed: remittance advice, claim copy, LCD/policy article excerpt,
order, [testing log / notes], same-or-similar printout.

[Name, credentials]  [Practice / supplier, NPI]  [Phone / email]

CO-151 prevention checklist

• Look up the LCD and policy article frequency before you dispense or schedule repeat services.
• Check MUE unit maximums for the HCPCS on that date of service.
• Review prior paid claims and date spans for overlap.
• Run Same or Similar (DME) in the portal or IVR before shipping.
• Set PM edits for common frequency ceilings by payer.
• Obtain an ABN when you expect Medicare won’t cover the frequency.
• Keep orders, delivery tickets and usage logs ready for appeal.
• Track CO-151 by HCPCS and site to target training.

Related denial codes

• CO-50: medical necessity denial; often paired with N115 for an LCD.
• CO-96: non-covered charge.
• CO-252: payer needs an attachment or documentation.
• CO-16: claim lacks information; fix data and resubmit.
• CO-236: procedure/service not payable under this benefit.
• PR-204: not covered under the patient’s current benefit plan.

In short

CO-151 means the units or the frequency look too high. Read the remark code. Check the LCD and the unit limit. Fix the date span or the units. Appeal only when you have proof of need.

FAQ

Quick facts

Item	Value
X12 code	151
X12 start	10/31/2002
Last reviewed	9 October 2026
Page type	WordPress Page under Denial Codes hub 183
Primary keyword	co-151 denial code

Named contractor sources include First Coast Service Options materials where linked, plus Novitas Solutions and Noridian Healthcare Solutions pages cited above.

Sources

• X12, Claim Adjustment Reason Codes (CARC 151, 150, 152, 119, 50, 57). CARC 151 Start 10/31/2002, Last Modified 01/27/2008. Accessed 9 Oct 2026.
• X12, Remittance Advice Remark Codes (N115, N130, M80). Accessed 9 Oct 2026.
• Noridian JA DME, Reason Code 151
• Noridian JA DME, Reason Code 151 | Remark Code N115
• Noridian JD DME, Reason Code 151 | Remark Code N115
• CMS, Medically Unlikely Edit (MUE)s (MUEs)
• CMS, Medicare Claims Processing Manual (IOM 100-04), Ch. 22, §60.1 Group Codes

Access dates and figures on this page were checked on 9 October 2026 against X12 and CMS sources.

Last reviewed: 9 October 2026 · This page is educational and doesn’t replace payer-specific instructions.