OA-2 Denial Code: Coinsurance Amount With Group Code OA

OA-2 is Claim Adjustment Reason Code 2 with group code OA. CARC 2 is the coinsurance reason code. Coinsurance is the share of an allowed amount that the patient pays after the plan pays its part. It usually comes back as PR-2, and the patient owes it. When the same reason comes back under OA, the remit does not say who owns the money. You have to work that out before you post it or bill anyone. Many people search for “oa 2 denial code”, and that is the phrase this page answers. (Primary sources: X12 Claim Adjustment Reason Codes · CMS Claims Processing Manual, Ch. 22, §60.1 · Medicare.gov, What Medicare costs)

Quick answer: OA-2 is not a denial. It is a coinsurance amount filed under “Other Adjustment.” Do not bill the patient from the OA-2 line alone. Check the math first: the amount should equal the plan’s coinsurance rate times the allowed amount left after the deductible. Then compare with the primary remit and decide who owns the balance.

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: 16 October 2026. Official code wording is quoted word for word from X12; Medicare rules link to their CMS source.

OA-2 denial code description (official X12 wording)

X12 Claim Adjustment Reason Code 2, verbatim:

“Coinsurance Amount”

Source: X12 Claim Adjustment Reason Codes, checked 16 October 2026. Start: 01/01/1995. X12 lists no later “Last Modified” date and no group code restriction for this code.

The group code is a separate field. X12 lists OA as “Other Adjustment.” CMS Claims Processing Manual, Ch. 22, §60.1 says OA “shall be used when no other group code applies to the adjustment.” CMS Transmittal 470 (2005) lists CARC 2 with group code PR.

What OA-2 means in plain English

• The reason is clear. A coinsurance amount was applied to the claim or line.
• The owner is not clear. The group code tells you who carries the amount. OA says only “other.”
• PR-2 is the usual pairing. CMS says the PR group “may be billed to the patient or insured.”
• OA-2 is the exception. Treat it as a line to check, not a line to post on autopilot.
• It is not a coverage decision. The service was covered, and the plan paid its share. Consider a routine office visit where the plan pays most of the allowed amount.

OA-2 vs PR-2, CO-2, OA-1 and lookalikes

Code	Official X12 idea	What it tells you
OA-2	Coinsurance Amount, group OA	Coinsurance with no stated owner. This page
PR-2	Coinsurance Amount, group PR	Patient (or a secondary plan) owes it. See PR-1, PR-2 and PR-3
CO-2	Coinsurance Amount, group CO	Contract write-off. See CO-2
OA-1	Deductible Amount, group OA	Deductible with no stated owner. See OA-1
3	Co-payment Amount	A flat copay, not a share of the allowed amount
OA-23	Impact of prior payer adjudication (OA only)	Prior payments and adjustments on a secondary remit. See OA-23

Check the coinsurance math first

Coinsurance is a rate applied to an allowed amount. Medicare.gov says Part B coinsurance is usually 20 percent of the cost of each covered service or item after the deductible, as long as the provider accepts assignment. Plans outside Medicare set their own rates, and your benefit check shows the rate.

Use this test on every OA-2 line:

1. Take the allowed amount for the line.
2. Subtract any deductible applied to the line.
3. Multiply what is left by the coinsurance rate.
4. Compare the result with the OA-2 amount.

If the numbers match, the amount really is coinsurance, and the open question is only who owns it. If they do not match, the payer may have mixed another adjustment, such as a copay or a prior payer amount, into the OA-2 line. Ask for a correction before you bill.

Who might own an OA-2 amount

X12 does not say why a payer picks OA for coinsurance, so confirm each case on your own remit.

1. The patient. The benefit details show the plan’s rate, and the math matches. The remit should have said PR-2, so ask the payer to confirm.
2. A secondary payer. On a crossover or secondary claim, the amount may be the part the primary left open. For example, Medigap usually helps pay Medicare coinsurance, per Medicare.gov.
3. A prior payer. The line may repeat an adjustment the primary payer already made. X12 puts those under CARC 23 with group OA.
4. The contract. If the agreement waives or absorbs the amount, the remit should say CO.

Where OA-2 shows up in the 835

CLP*PCN71002*2*200.00*120.00*0.00*12*CLAIM440218~
SVC*HC:99214*200.00*120.00**1~
CAS*CO*45*50.00~
CAS*OA*2*30.00~

• The line paid $120.
• CAS*CO*45*50.00 is a contractual reduction.
• CAS*OA*2*30.00 is the coinsurance amount in the OA group.
• The allowed amount is $150, because $200 minus $50 is $150.
• This sample is illustrative only. Real remits vary.

How to fix OA-2: decision path

1. Confirm the CAS segment. Check the group (OA), the reason (2), and the amount. Save the remit.
2. Check the math. Allowed amount, less deductible, times the coinsurance rate.
3. Compare with the primary remit if this is a secondary claim.
4. Check the benefit details for the patient’s rate and any out-of-pocket limit.
5. If the patient owes it, bill only that amount, and ask the payer to confirm it under PR.
6. If a secondary payer should pay it, send the claim and the primary remit to that payer.
7. If a contract adjustment covers it, post the write-off.
8. If the numbers do not tie, ask the payer to correct the group code or the amount.

Medicare, commercial and Medicaid notes

Medicare. CMS Transmittal 470 lists CARC 2 with PR, so an OA group on a Medicare remit deserves a question to the contractor. In CMS’s own secondary payer example (MSP Manual Ch. 3, §10.1.2), the Part B payment is 80 percent after the deductible, which leaves coinsurance of 20 percent.

Commercial. Plans set coinsurance rates and out-of-pocket limits. Ask the payer for the rate it applied and whether the patient has reached the limit.

Medicaid. Each state sets its own rules for what it pays toward other coverage. Check the state provider manual.

Worked example (illustrative)

A practice bills 99214 for $200. The plan allows $150, pays $120, and reports CAS*OA*2*30.00. The deductible was already met, and the plan’s coinsurance rate is 20 percent.

Reading it: The allowed amount is $150. Twenty percent of $150 is $30, so the OA-2 amount matches the plan’s rate.

Check: The benefit details show a 20 percent rate and no out-of-pocket limit reached. No secondary plan is on file.

Action: The biller bills the patient $30, and sends the payer a note asking why coinsurance came back under OA instead of PR.

Second scenario: The patient also has a secondary plan. The biller sends the secondary plan the claim and the primary remit, and holds the patient bill until the secondary plan pays.

Prevention checklist

• [ ] Check the benefit rate at eligibility, so the math can be tested later.
• [ ] Hold patient statements on any OA line until it is checked.
• [ ] Compare each secondary remit with the primary remit.
• [ ] Track OA-2 by payer to find wrong group code use.
• [ ] Ask the payer to explain any OA-2 line that does not tie out.
• [ ] Keep the CARC and RARC guide handy for staff training.

Related denial codes

• PR-1, PR-2 and PR-3: deductible, coinsurance and copay under patient responsibility.
• CO-2: coinsurance under the contractual group.
• OA-1: the deductible under group OA.
• OA-23: impact of prior payer adjudication.
• CARC and RARC guide.

Key takeaways

OA-2 is coinsurance with no named owner. Check the math against the allowed amount and the plan rate. Compare it with the primary remit. Then bill the patient, bill a secondary payer, or write it off.

FAQ

Quick facts

Item	Value
X12 code	2
X12 start	01/01/1995
Official wording	Coinsurance Amount
Group on this page	OA
CMS 2005 group for CARC 2	PR
Common confusions	PR-2 (patient group), CO-2 (contract), CARC 3 (copay)
Last reviewed	16 October 2026

Sources

• X12, Claim Adjustment Reason Codes (CARC 1, 2, 3, 23, 45). CARC 2 Start 01/01/1995. Accessed 16 Oct 2026.
• CMS, Medicare Claims Processing Manual (IOM 100-04), Ch. 22, §60.1 Group Codes. Accessed 16 Oct 2026.
• CMS, Transmittal 470 (4 Feb 2005). Accessed 16 Oct 2026.
• CMS, Medicare Secondary Payer Manual (IOM 100-05), Ch. 3, §10.1.2. Accessed 16 Oct 2026.
• Medicare.gov, Costs (Part B coinsurance, Medigap). Accessed 16 Oct 2026.
• Medical Billing 101, OA-1 guide.

Code wording and Medicare rules on this page were checked on 16 October 2026 against X12, CMS and Medicare.gov sources.

Last reviewed: 16 October 2026 · This page is educational and doesn’t replace payer-specific contracts or coding rules.

Related denial codes

• PR-2: Coinsurance Amount (Patient Responsibility)
• CO-2: Coinsurance Amount (When the Group Code Is CO)
• PR-1, PR-2 and PR-3: Deductible, Coinsurance and Copay (Patient Responsibility)
• PR-3: Copay Amount, Posting and Refunds
• OA-1: Deductible Amount With Group Code OA
• CO-3: Co-payment Amount (When the Group Code Is CO)
• CO-1: Deductible Amount (When the Group Code Is CO)
• PR-66: Blood Deductible the Patient Owes

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