Medical coding
How to audit medical coding accuracy: sample sizes, error rates and credential checks
To audit medical coding accuracy, OIG’s guidance for physician practices gives a basic guide of five or more records per federal payor or five to ten per physician, with no set formula, a baseline audit and at least one audit a year. Its guidance for billing companies asks for a valid statistical sample, reviewed before and after billing by a qualified coding expert. No OIG or CMS text read sets an accuracy percentage: 95% is an industry benchmark. The practice stays responsible for claims sent in its name. This is general information, not legal advice. Review your payer contracts and the rules where you practice with your compliance advisor.
Published by OffshoreMeds. Facts last checked October 10, 2026. How we check our numbers.
The guidance
What OIG says about sampling and audits
| Question | What the guidance says | Source |
|---|---|---|
| Question: How many records? | What the guidance says: There is no set formula. A basic guide is five or more medical records per federal payor, or five to ten per physician, and a larger sample gives more comfort. The sample may be drawn from all of a physician's or payor's claims. | Source: 65 FR 59437 |
| Question: How often? | What the guidance says: A baseline audit of claims submitted and paid in the first three months after training, then periodic audits at least once each year. | Source: 65 FR 59437 |
| Question: What is tested? | What the guidance says: That bills are accurately coded and reflect the services documented in the record, and the documentation and medical necessity behind them. The audit examines the claim path from patient intake to payment. | Source: 65 FR 59437 |
| Question: What a billing company should do | What the guidance says: At a minimum, review a valid statistical sample of claims each year, both before and after billing is submitted, with the review done by a qualified expert in the applicable coding process. | Source: 63 FR 70144 |
| Question: What to do with a finding | What the guidance says: Respond quickly, repay any overpayment, and consider an outside coding or billing expert. Overpayments a billing company finds are reported promptly to the provider with an explanation. | Source: 65 FR 59438 |
Both documents are voluntary guidance. The physician-practice sample is per physician or per payor, not per coder, so it should not be read as a sample size for one coder. The billing-company guidance is addressed to the billing company, which makes it a list of what a practice can ask a vendor for.
The number
No source sets an accuracy percentage
The figure the coding page uses, 95%, comes from a Journal of AHIMA article that calls it a common benchmark and the de facto standard for medical coding. The same article says results can vary widely depending on the method used, and advises defining the numerator and denominator for an accuracy rate and collecting the data consistently. Its worked example, one author reviewing 25 inpatient cases, found 28% of cases right on all audit elements when each record had to be correct throughout, against 91.18% to 92.42% when each code was counted alone. So the first question for any quoted rate is what was counted: codes, claims or records, weighted or not.
A common mix-up
The Medicare error rate is not a coder accuracy rate
CMS’s Comprehensive Error Rate Testing program reviews a statistically valid sample of Medicare fee-for-service claims to see whether they were paid properly under coverage, coding and payment rules. The fiscal year 2025 improper payment rate was 6.55%, and incorrect coding accounted for 0.7% of payments, with documentation errors the larger share (CMS CERT). It is a dollar-weighted payment measure for one program and includes documentation, medical necessity and non-response errors that a coder cannot fix, so it is not comparable with a per-code accuracy rate.
Credentials
Checking a coder's credential, and what the lookup returns
| Body | How to look it up | What it returns | Source |
|---|---|---|---|
| Body: AAPC | How to look it up: A member ID and last name, or an email and last name. A name alone is not enough. | What it returns: The credential, the date earned, the renewal date and the status. AAPC disclaims the accuracy of the results and says the user must make sure they apply to the right person. | Source: AAPC verification |
| Body: AHIMA | How to look it up: A last name and either a credential number or an AHIMA ID. | What it returns: The credential, program, dates and current status. | Source: AHIMA verification |
- AAPC says a person without two years of coding experience who passes the CPC exam receives the CPC-A credential, so a coder presented as fully certified should show CPC.
- Credentials need continuing education: AAPC lists 36 CEUs every two years for one certification and verifies a random quarter of submissions, and AHIMA lists 20 CEUs per two-year cycle for the CCS.
- The lookups were not run on a live record for this guide, so the output described comes from the pages themselves.
In practice
What to ask a coding vendor for, and what stays with the practice
- The sampling method: how records are drawn, by payer and by coder, and how large the sample is.
- The definition of accuracy: what is counted, and the numerator and denominator.
- Who reviews the sample, and that person’s credential, which should be independent of the coder.
- A review before billing as well as after, and the written error log with its corrective action.
- How an overpayment found in a sample is reported to you and repaid.
OIG says physicians remain responsible to the Medicare program for bills sent in their name, and that a billing service’s error is no defense (65 FR 59447); the same page repeats OIG’s concern about percentage-based compensation, which the medical billing percentage of collections page covers. What offshore coders do is on the offshore medical coding staff page, and the question list is in offshore medical billing vendor questions. This is general information, not legal advice. Review your payer contracts and the rules where you practice with your compliance advisor.
The terms behind each seat
One flat monthly fee per seat, never a percentage of collections. A Business Associate Agreement is signed before anyone touches protected health information. Clinical decisions stay with your US-licensed providers. See all OffshoreMeds services.
Related guides
- Offshore medical coding staff
ICD-10, CPT and HCC coders working in your EHR, audited daily against a published accuracy standard.
- Percentage-of-collections fees
How the fee works, what Medicare, Medicaid and the OIG say about paying a billing agent, and questions to ask before you sign.
- Vendor questions before you sign
Questions on contract, access, location, payer rules, pay and exit, each tied to the rule or source behind it.
- How to outsource medical billing
Five steps from choosing roles to go-live, with the compliance and cost checks in the right order.
- Medicare Advantage RADV audits
What RADV checks and how it is scored, the 2024 CMS-HCC model, the vacated 2023 rule and OIG's guidance on coding vendors.
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