X12 270/271: how electronic eligibility checks work

What are the 270 and 271?

The eligibility transaction is an inquiry from a health care provider to a health plan to obtain eligibility, coverage, or benefit information for an enrollee, and the plan's response (45 CFR Part 162). The inquiry is the X12 270 and the response is the X12 271. Both use version 5010 (implementation guide 005010X279; Medicare's HETS uses the 005010X279A1 errata version) (HETS Companion Guide).

A practice usually sends a 270 through its practice management system, EHR, or clearinghouse, which routes it to the right payer. The payer answers with a 271, or with an error if it cannot match the patient.

What a 271 response tells you

Under the CORE operating rules HHS adopted, a 271 must return at least (CORE 154; CORE 260):

• Whether the patient has active coverage, and the plan coverage dates
• The health plan name
• Patient financial responsibility (copayment, coinsurance, and deductible) for each service type returned, for both in-network and out-of-network care
• Base and remaining deductible amounts

Medicare's 271 also returns Part A and Part B entitlement and, where applicable, Medicare Secondary Payer, Medicare Advantage, and Part D plan enrollment (HETS Companion Guide). That is how a practice learns that a patient it thought was on traditional Medicare is actually in a Medicare Advantage plan, which often has its own prior authorization rules.

Service type codes: asking the right question

A 270 can ask about benefits for a specific type of service using a service type code (STC). A generic inquiry uses STC 30, Health Benefit Plan Coverage. Under the Phase I CORE rule, a plan must answer a generic STC 30 inquiry with benefits for a required set of service types: 33 Chiropractic, 47 Hospital, 48 Hospital - Inpatient, 50 Hospital - Outpatient, 86 Emergency Services, 98 Professional (Physician) Visit - Office, and UC Urgent Care (CORE 154). The Phase II rule expanded the list to 51 service types that must be supported when asked for explicitly (CORE 260).

Asking with the specific STC for the visit, such as MH for mental health or AL for vision, returns more precise cost-share information than a generic check. The X12 codes guide lists the common STCs.

Speed: real-time and batch rules

Health plans and clearinghouses must meet response-time rules that HHS adopted in 2011, effective January 1, 2013 (45 CFR Part 162):

• Real-time: the maximum response time for a 271 is 20 seconds or less, measured over a calendar month (CORE 156).
• Batch: inquiries submitted by 9:00 pm Eastern time on a business day must be answered by 7:00 am Eastern time the next business day (CORE 155).

Later versions of the CORE eligibility rules exist, but only the 2011 versions are federally required; newer versions are voluntary (CORE operating rules). Since October 2026, X12 administers the CORE rules (X12).

Checking Medicare eligibility through HETS

For traditional Medicare, CMS runs the HIPAA Eligibility Transaction System (HETS), which returns Medicare beneficiary eligibility in real time. HETS does not accept batch transactions (CMS). Providers, clearinghouses, and third-party vendors connect to it as trading partners with CMS (HETS Companion Guide).

HETS accepts only the Medicare Beneficiary Identifier (MBI) as the subscriber ID; the older HICN is rejected. A standard search combines the MBI, date of birth, and full last and first name, and the MBI and last name are always required (HETS Companion Guide). If no service type is requested, or HETS does not support the one requested, it answers as if STC 30 had been sent. HETS data is refreshed once a day.

When a 270 is rejected: AAA errors

If a payer cannot process an inquiry, the 271 returns an AAA segment with a reject reason code instead of benefits. Under the CORE rules, payers must use specific codes for common failures, such as 72 Invalid/Missing Subscriber/Insured ID and 75 Subscriber/Insured Not Found (CORE 259).

HETS documents a follow-up action for each code: "retry later" for 42 and "correct and resubmit" for the data errors (HETS Companion Guide). More codes are in the X12 codes guide.

Making eligibility checks part of the workflow

1. Identify the right payer and plan from the referral, insurance card, or chart before sending anything.
2. Send a real-time 270 with the service type that matches the visit, not only STC 30.
3. Record coverage dates, cost share, and any Medicare Advantage or secondary payer information to the chart.
4. Work AAA rejections the same day: most are data errors that can be fixed and resubmitted.
5. Re-verify before the visit when coverage could have changed, such as at the start of a plan year.

Saga's agents follow this workflow: they select the correct payer and plan, run real-time X12 270/271 checks, record benefits to the chart, flag problems for staff, and re-verify before each visit. See eligibility verification.