How to Read an 835 and Turn Its Denials Into a Worklist

835 (ERA): the ASC X12 Health Care Claim Payment/Advice transaction, adopted in version 5010 as the national HIPAA standard for electronic remittance advice, which reports what a payer paid on each claim and codes every adjustment with a group code, a claim adjustment reason code (CARC) and, where needed, remittance advice remark codes (RARCs).

Undeny's Take

Most practices read remits one check at a time, posting payments and skimming past the zero-pay lines. That is how denials age out. The 835 already contains everything you need to triage: the claim, the dollars, the reason, and the date of the decision. What it does not give you is a due date, and that is the one field that decides which denial you work first. A billing company working ten client practices gets ten different payer mixes and ten sets of deadlines from the same file format, so the worklist has to be built from the 835 itself, not from memory of which payer is slow.

The Four Segments That Matter for Denials

An 835 is long, but denial work lives in a handful of segments. CMS describes the X12 835 as "a variable-length record designed for wire transmission," which is why you read it through your practice management system or clearinghouse viewer rather than as raw text.

CLP: the claim

Each claim on the remit starts with a CLP segment. It carries your patient account (claim) number, the claim status, the billed charge, and the paid amount. CMS identifies CLP04 as the "Calculated Payment to Provider." A CLP with a paid amount of zero and adjustments equal to the charge is your first signal of a full denial.

CAS: every unpaid dollar, with a reason

CAS segments hold the adjustments. Each one names a group code, then a CARC and the dollar amount. CMS notes that the 835 allows only one reason code to explain any one specific adjustment amount, so a claim that was cut for two reasons shows two adjustments. CAS can appear at claim level or at service-line level.

SVC: the service line

SVC repeats the procedure code, the line charge and the line payment, followed by its own CAS adjustments. For therapy and outpatient claims with several units or codes, denials often sit at line level, so read SVC and its CAS together rather than relying on the claim total.

LQ, MOA and MIA: the remark codes

Remark codes explain the reason code. CMS requires service-line remark codes in the LQ segment, and remark codes that apply to the whole claim in MOA (non-inpatient) or MIA (inpatient). The implementation guide allows up to 5 remark codes in MOA/MIA and up to 99 in LQ. A remark such as "missing/incomplete/invalid" usually tells you the exact field to correct.

What CO, PR, OA and PI Mean for Reimbursement and the Member

X12 maintains four claim adjustment group codes. CMS defines the three Medicare uses in the Claims Processing Manual, chapter 22:

Group code	X12 name	What it means for your worklist
CO	Contractual Obligation	A contract or regulatory requirement caused the adjustment. CMS says these are "generally" a write-off and are "not billed to the patient." Apart from expected contractual write-offs, CO denials are yours to fix or appeal.
PR	Patient Responsibility	An amount that "may be billed to the patient or insured," typically deductible and copay. Medicare beneficiaries may be billed only when PR is used.
OA	Other Adjustment	Used "when no other group code applies." Review each one; some are informational, some are recoverable.
PI	Payor Initiated Reduction	A reduction the payer initiated. Read the reason code before deciding whether to dispute it. Medicare's manual lists only CO, OA and PR.

A CO-45 (charge exceeds the fee schedule) is normally a contractual write-off, not a denial to appeal. A CO-16 (missing information) is usually fixable with a corrected claim. A PR-1 deductible goes to patient billing. Learning that split is most of how to read an 835 quickly.

Reason and Remark Codes Change Three Times a Year

The CARC list is maintained by the Claim Adjustment Status and Reason Code Maintenance Committee and, per CMS, updated three times a year. Both CARC and RARC lists are updated on or around March 1, July 1 and November 1. CAQH CORE operating rules also standardize which CARC and RARC combinations payers use on the 835, maintained in a list updated three times a year. Check codes against the current X12 lists, not a printed cheat sheet.

How to Build a Denial Worklist From 835s

1. Pull every 835 for the period from your clearinghouse, not only the ones attached to deposits, so zero-pay remits are included.
2. For each CLP, list every CAS adjustment at claim and service-line level with its group code, CARC, amount, and any LQ or MOA remark codes.
3. Drop the expected adjustments: CO-45 contractual write-offs and PR deductible, coinsurance and copay amounts that belong in patient billing.
4. Classify what remains: fixable with a corrected claim (missing or invalid data), appealable (medical necessity, authorization, coding disputes), or needs a call to the payer.
5. Assign each denial its deadline. Appeals use the payer's appeal window, counted from the remit or denial date; corrected claims usually must still meet the payer's timely filing limit. For Medicare, remark MA01 states an appeal must be filed "within 120 days of the date you received this notice."
6. Sort the list by days remaining, then by dollars, and draft the appeal or corrected claim for each, starting with the nearest deadline. The appeal letter generator drafts the letter from the codes.

Check that each remit balances before trusting it: CMS states that the total paid must equal total submitted charges plus or minus adjustments, at the service, claim and provider levels.

For Billing Companies Working Many Practices, In or Out of Network

When you bill for several client practices, the same steps run across every client's remits, and the worklist becomes the shared queue your team works from. If you want to see what that looks like, see a sample denial worklist built from 835s, with fictional data. Undeny's founding pilot for billing companies takes one client practice's 835 remits and returns every denial sorted by appeal deadline, each with a drafted appeal or corrected claim, at $149 for a refundable first month, then $149 per client practice per month including 25 denials worked and $6 for each one after that. Details are on the billing companies page.

Frequently Asked Questions

What is an 835 remittance advice?

An 835 is the ASC X12 Health Care Claim Payment/Advice transaction, the electronic version of an explanation of benefits sent to providers. CMS adopted X12 835 version 5010 as the national HIPAA standard for electronic remittance advice. It lists each claim paid or denied, the amounts, and coded reasons for every adjustment.

Where are the denial codes in an 835 file?

Denial reasons are in the CAS segments, which hold a group code, a claim adjustment reason code and the adjusted amount. CAS can sit at claim level after CLP or at line level after SVC. Remark codes that add detail are in LQ for service lines and in MOA or MIA for the whole claim.

What is the difference between CO and PR on an 835?

CO means Contractual Obligation: a contract or regulation caused the adjustment, and CMS says it is generally not billed to the patient. PR means Patient Responsibility: the amount may be billed to the patient, typically deductible and copay. CO amounts are the provider's to write off, correct or appeal.

How many reason codes can one adjustment have?

One. CMS notes that the X12 835 allows only one reason code to explain any one specific adjustment amount. If a payer reduced a line for two reasons, you will see two separate adjustments, each with its own reason code and amount.

How often do CARC and RARC codes change?

Both lists are updated three times a year, on or around March 1, July 1 and November 1, according to the Medicare Claims Processing Manual. New codes are added and old ones deactivated, so check codes against the current X12 lists rather than an old reference.

How do I prioritize denials from 835 files?

Remove expected adjustments such as contractual write-offs and patient responsibility, then give every remaining denial its deadline: the payer's appeal window for appeals, and the timely filing limit for corrected claims. Sort by days remaining, then by dollars, and work from the top.

Informational only, not legal, medical, or billing advice. Segment usage, code lists and appeal deadlines vary by payer and change over time; verify against the X12 implementation guide, the payer's companion guide and current payer policy.

Turn 835s Into a Worked Denial List

See what every denial on a client's remits looks like once it is sorted by deadline and drafted. See a sample denial worklist built from 835s · Founding pilot for billing companies · Generate an appeal