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Return Unprocessable Claim (RUC) Reason Code CO 16 FAQ
Last Modified: 3/19/2024
Location: FL, PR, USVI
Business: Part B
Q: We received a claim rejected as unprocessable (RUC) with claim adjustment reason code (CARC) CO 16. What steps can we take to avoid this RUC code?
CO 16: Claim/service lacks information or has submission/billing error(s).
Usage: Do not use this code for claims attachment(s)/other documentation. At least one Remark Code must be provided (may be comprised of either the NCDPD Reject Reason Code, or Remittance Advice Remark Code that is not an ALERT.) Refer to the 835 Healthcare Policy Identification Segment (loop 2110 Service Payment Information REF) if present.
A: This RUC is received when a claim is submitted with missing, incorrect, or invalid information. For details pertaining to your claim, please refer to the remittance advice remark codes (RARCs) on the remittance advice (RA). Then click on the topic(s) listed below, as applicable, for steps you may take to correct the error(s) and prevent the RUC in the future.
Resources for general information regarding claim completion and requirements:
Claims rejected as unprocessable will include message code N211 on the RA stating “Alert: You may not appeal this decision.” For more information, click here. To avoid delay in payment and prevent a denial for untimely filing, submit a corrected claim. Per Medicare guidelines, claims must be filed with the appropriate claims Medicare processing contractor no later than 12 months after the date of service. RUCs are not considered filed/submitted. Click here for details regarding timely filing. Beneficiary name, SSN, and/or Medicare number/Medicare Beneficiary Identifier (MBI)/health insurance claim number (HICN) MA27: Missing/incomplete/invalid entitlement number or name shown on the claim.
MA36: Missing/incomplete/invalid patient name.
MA61: Missing/incomplete/invalid Social Security number.
N382: Missing/incomplete/invalid patient identifier.
• Refer to Item 1a on the claim form. Enter the patient’s Medicare number as indicated on the patient’s Medicare card. For claims submitted on or after January 1, 2020: Use patient MBI, regardless of date of service. Refer to CMS MLN Matters® number
SE18006 
• Refer to Item 2 on the claim form. Enter the patient’s name (last name, first name, and middle initial-if any) as indicated on the patient’s Medicare card.
• Include spaces and special characters if indicated on Medicare card. Exception: PC-ACE software currently does not accept special characters; enter space instead.
N256: Missing/incomplete/invalid billing provider/supplier name.
N257: Missing/incomplete/invalid billing provider/supplier primary identifier.
N258: Missing/incomplete/invalid billing provider/supplier address.
MA112: Missing/incomplete/invalid group practice information.
• Refer to Items 33 and 33a on the claim form. These are required fields. Enter the billing provider/supplier name, address, zip code and telephone number in Item 33, and the billing provider/group NPI in Item 33A.
• Do not enter anything in the Item 33b.
M79: Missing/incomplete/invalid charge.
• Refer to Item 24F on the claim form. Medicare does not pay for services when a charge is not indicated. Enter a charge for each service listed on the claim.
CLIA certification number MA120: Missing/incomplete/invalid CLIA certification number.
• Independent clinical diagnostic laboratory (specialty code 69) must be properly certified to submit laboratory services.
• Click here 
for a listing of procedures that require CLIA certification.
• CMS
laboratory demographics lookup can be used to search for information about where the laboratory testing is performed, including CLIA number, certification type, and expiration dates.
• CLIA certification numbers have the letter “D" in the third position.
• Paper claim (CMS-1500) submission requirements:
• Enter a valid 10-digit CLIA certification number in item 23.
• Only one CLIA number may be submitted on a single paper claim. Therefore, the laboratory must submit two claims:
• Report the billing laboratory’s CLIA number on one claim for tests performed onsite.
• Report the reference laboratory’s CLIA number on a separate claim for tests that were referred.
• Electronic claim submission requirements:
• Independent laboratories report the CLIA number for performed services in X12N 837 loop 2300, and the “X4” qualifier in the REF (reference identification) segment.
• Example: REF*X4*12D4567890
• The CLIA numbers for both the referred and performed services must be submitted on the same electronic claim.
• The billing laboratory’s CLIA number is reported in loop 2300 with the “X4” qualifier in the REF segment.
• The reference laboratory’s CLIA number is reported in loop 2400 with the “F4” qualifier in the REF segment.
• Refer to CMS MLN Matters number
MM3090 for additional billing guidance.
Date range not valid with units submitted M52: Missing/incomplete/invalid –from- date(s) of service.
N345: Date range not valid with units submitted.
• Refer to Item(s) 24A and/or 24G on the claim form. Ensure date(s) of service (DOS) correspond(s) to the number of units/days billed. If billing for more than one unit on a single day, services may need to be itemized, one per line.
Facility ZIP code or state code • Refer to Item 32 on the claim form. Service facility information is used to price claims. Enter the state code and ZIP code on the claim.
• Click here to see if a 9-digit ZIP code is needed for the facility.
• The state code should be referred to as the province code for providers in U.S. Virgin Islands.
• Click here to review the Contractor Directory - Interactive Map to access state-specific CMS contractor contact information.
Facility/laboratory name and/or address N294: Missing/incomplete/invalid service facility primary address.
MA114: Missing/incomplete/invalid information on where the services were furnished.
• Refer to Item 32 on the claim form. Service facility information is used to price claims. Enter the service location name and complete address on the claim.
• Enter the service location name, street address, city, state, and a valid ZIP code in item 32.
• The location where the service was rendered is required for all place of service (POS) codes.
• If additional entries are needed, separate claim forms must be submitted.
• If required by Medicare claims processing policy, enter the service facility NPI in item 32a.
Purchased service/primary provider identifier N270: Missing/incomplete/invalid another provider primary identifier.
N283: Missing/incomplete/invalid purchased service provider identifier.
Effective for claims submitted with a receipt date on and after October 1, 2015, billing physicians and suppliers must report the name, address, and NPI of the performing physician or supplier on all anti-markup and reference laboratory claims, even if the performing physician or supplier is enrolled in a different contractor’s jurisdiction.
• Enter the valid performing physician/supplier NPI in item 32a.
• Enter the performing physician/supplier name, address, and ZIP code in item 32.
• Click here for additional guidance on billing anti-markup and reference laboratory claims.
Note: Do not combine non-referred (i.e., self-performed) and referred services on the same CMS 1500 claim form. Submit two separate claims, one for non-referred tests and another for referred tests.
M76: Missing/incomplete/invalid diagnosis or condition.
M81: You are required to code to the highest level of specificity.
• Refer to Item 21 on the claim form. Enter the ICD Indicator and diagnosis code on the claim.
• Enter the appropriate ICD Indicator as a single digit between the vertical, dotted lines.
• Indicator ‘9’ is used for ICD-9-CM diagnosis codes.
• Indicator ‘0’ is used for ICD-10-CM diagnosis codes.
• Enter up to 12 diagnosis codes in priority order. The diagnosis codes must be coded to the highest level of specificity.
• Use the most current year's ICD-9-CM or ICD-10-CM codes, depending on the date(s) of service.
• Do not insert a period in the ICD-9-CM or ICD-10-CM codes.
Example: Diagnosis code 285.21 is entered as 28521, without a period or space.
• Reminder: Do not report ICD-10-CM codes for claims with date(s) of service prior to October 1, 2015.
Incorrect claim form/format N34: Incorrect claim form/format for this service.
• Refer to Items 11b, 12, 14, 16, 18, 19, 24A and 31 on the claim form. You have the option to enter either a 6-digit (MMDDYY) or 8-digit (MMDDCCYY) date. However, you must be consistent with the date format throughout the entire claim, including the provider portion.
• If you choose the 6-digit format for the first date field in the claim, that 6-digit format must be used in all subsequent date fields.
• If you choose the 8-digit format for the first date field, the 8-digit format must be used in all subsequent date fields.
Ordering or referring physician name, qualifier and/or NPI N264: Missing/incomplete/invalid ordering provider name.
N265: Missing/incomplete/invalid ordering provider primary identifier.
N276: Missing/incomplete/invalid another payer referring provider identifier.
N285: Missing/incomplete/invalid referring provider name.
N286: Missing/incomplete/invalid referring provider primary identifier.
• Refer to Items 17 and 17b on the claim form.
• Enter the name of the referring, ordering or supervising physician in Item 17. Enter the individual provider’s name—not the group name.
• Per National Uniform Claim Committee (NUCC) instructions, if there is more than one provider (referring, ordering, and supervising) applicable to the service, the provider should be picked based on this order: referring, ordering, and supervising. For more information, visit the
NUCC website , and refer to the NUCC 1500 claim form instructions.
• Enter one of the following qualifiers appropriate to identify the role of the physician/non-physician practitioner in Item 17 to the left of the dotted vertical line.
• DN: Referring provider
• DK: Ordering provider
• DQ: Supervising provider
• Enter the corresponding NPI for the individual provider indicated in Item 17b. Do not enter the group NPI in this field.
Physician/supplier signature MA81: Missing/incomplete/invalid provider/supplier signature.
• Refer to Item 31 on the claim form. The physician/non-physician practitioner signature is required. The following formats are acceptable.
• Actual signature
• “Signature on file” notation (if applicable)
• Computer-generated signature
Primary or secondary payer information MA83: Did not indicate whether we are the primary or secondary payer.
• Refer to Item 11 on the claim form. This is a required field. By completing this item, the physician/supplier acknowledges that he/she made a good faith effort to determine whether Medicare is the primary or secondary payer.
• If Medicare is primary, enter the word “NONE.”
• If Medicare is secondary, enter the insured’s policy or group number, and continue to Items 11a -11c.
• Note: Items 4, 6 and 7 on the claim form must also be completed.
M51: Missing/incomplete/invalid procedure code(s).
• Refer to Item 24D on the claim form. Select a valid procedure code using the most current year's CPT and/or HCPCS code(s) based on the date(s) of service on your claim.
• Check code status via our
fee schedule lookup tool to confirm the procedure code is valid for Medicare. Be aware that code status may change, so a procedure code that was previously valid for Medicare may no longer be valid.
• If the procedure code has an “I” status, the procedure code is not valid for Medicare and should not be billed unless documentation is needed for a secondary payer or supplemental plan.
• Click here for additional information regarding procedure codes.
N290: Missing/incomplete/invalid rendering provider primary identifier.
MA112: Missing/incomplete/invalid group practice information.
• Refer to Items 24J and 33 on the claim form.
• For services rendered by a provider in a group: Enter the individual provider NPI in Item 24J in the unshaded portion of this field. Do not report anything in the upper shaded portion. Do not enter the group NPI in this field. (Billing group NPI goes in Item 33a.)
• Rendering provider must be associated with group indicated in Item 33.
• For services rendered by a non-physician practitioner (e.g., laboratory technician, ultrasound technician, radiology technician), enter the supervising physician NPI.
• Enter the billing group name, address, zip code, and telephone number in Item 33.
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