Medicare Secondary Payer ESRD Rules: The 30-Month Coordination Period and How to Bill It

The Medicare Secondary Payer ESRD rule says that when a patient has Medicare because of end-stage renal disease and also has group health plan (GHP) coverage, the plan pays first and Medicare pays second for a 30-month coordination period. It is the one Medicare Secondary Payer rule where the employer’s size and the patient’s job status do not matter.

Every dialysis unit and nephrology practice has a handful of these patients at any time, and Medicare becomes primary on a date you can calculate in advance. Most of the work is knowing that date.

Where you see it

Place	What it shows
MSP questionnaire, Part III	The ESRD questions: dialysis start date, transplant date, GHP coverage, and whether the patient is within the 30-month period
271 eligibility response	Medicare’s record of a primary GHP, with its effective dates
CMS-1500 boxes 9 and 11	The other insured and the primary plan; 11d marked yes
837P loop 2320	The primary payer with SBR01 P, insurance type code 13 (ESRD), the plan’s CAS adjustments and AMT D paid amount
837P loop 2330B	The primary plan’s name and payer ID
Remittance advice	OA-23 for the prior payer’s impact on a secondary payment; CARC 22 with MA04 when Medicare needs primary information; CARC 109 when Medicare’s record shows another payer is primary

Who pays first and for how long

Situation	Primary	Secondary
Medicare based on ESRD only, GHP coverage of any kind	GHP, for 30 months	Medicare
Same patient after the 30th month	Medicare	GHP
ESRD plus COBRA or retiree coverage during the 30 months	COBRA or the retiree plan	Medicare
Age or disability entitlement first, GHP already primary because of current employment, then ESRD	GHP, for the 30 months of ESRD eligibility, then Medicare	Medicare, then GHP
Age or disability entitlement first, Medicare already properly primary (retiree, or small employer), then ESRD	Medicare, during and after the period	GHP
Age or disability entitlement and no GHP, then ESRD, then GHP coverage obtained during the period	Medicare	GHP
ESRD first, then the patient turns 65 during the period	The period continues; Medicare becomes primary after month 30

The Medicare Secondary Payer Manual states that Medicare is secondary during the period even if the plan’s contract says its benefits are secondary to Medicare, and the plan may not treat ESRD patients differently from other members. The rule covers all Medicare-covered items and services for the patient during the period, including care unrelated to the kidneys.

Counting the 30 months

The period begins with the first month the patient is eligible for Medicare Part A on the basis of ESRD, whether or not an application has been filed. CMS’s ESRD page gives the usual starting points:

• In-center dialysis: Medicare eligibility begins the fourth month of dialysis. Dialysis that starts in March makes June the first month, and the period runs through November two years later.
• Home dialysis training: eligibility can begin the first month of dialysis if the patient starts a Medicare-approved training program before the third month and is expected to complete it and self-dialyze.
• Transplant: eligibility can begin the month of admission for a Medicare-approved transplant or pre-transplant care, if the transplant takes place that month or in the following two months.

A new 30-month period starts each time the patient becomes eligible again on the basis of kidney failure. ESRD-only entitlement ends 12 months after the month dialysis stops, or 36 months after the month of a transplant.

The MSP questionnaire

Providers must find out whether Medicare is primary before billing it, by asking the patient or checking eligibility, at every admission, outpatient encounter or start of care. The model questions in the MSP Manual, Chapter 3, section 20.2.1, have a Part III for ESRD. The questions are whether the patient has GHP coverage through themselves, a spouse or a family member; whether and when they received a transplant; whether and when maintenance dialysis began; whether they are within the 30-month period; and whether they had the GHP coverage before Medicare entitlement. Part III also collects what the claim needs: the employer’s name and address, the plan’s name and address, the policy and group numbers, and the policyholder’s name and relationship.

Keep the answers for 10 years. Report a new plan, a job change or a plan termination to the Benefits Coordination and Recovery Center at 1-855-798-2627 so Medicare’s record matches what you bill.

Billing the plan, then Medicare

Bill the GHP first, as the primary payer, with an itemized claim. When its remittance arrives, build the Medicare claim from it. The Claims Processing instructions for physicians and suppliers in MSP Manual Chapter 3, section 30.5, call for:

What Medicare needs	Where it goes on the 837P
The primary payer and its order	Loop 2320 SBR with SBR01 P for the plan; Medicare is S in loop 2000B
The MSP reason	Insurance type code 13, ESRD, in the 2320 SBR
What the plan paid	Loop 2320 AMT with qualifier D for the claim, or loop 2430 SVD02 for each line
What the plan allowed and adjusted	CAS segments with the plan’s group and reason codes; CO 45 carries the contractual amount, and PR 1, 2 or 3 the patient’s deductible, coinsurance or copay
The plan’s identity	Loop 2330B

On a paper claim, attach the plan’s explanation of benefits. If the plan paid at least what Medicare would have allowed, Medicare owes nothing further. If the plan denied the claim because the service is not a plan benefit for anyone, Medicare may pay as primary with the denial attached. If the plan reduced its payment because the practice failed to file a proper claim, Medicare bases its secondary payment on what the plan would have paid, and the patient cannot be billed for the difference.

Worked example: Ms. Rivera

Ms. Rivera, 58, started in-center hemodialysis on March 12, 2026. She has coverage through her own job at a 15-person company. Employer size does not matter under the ESRD rule, so the plan is primary.

Step	Date	Why
Dialysis begins	March 12, 2026	Month 1 of dialysis
Medicare ESRD eligibility	June 1, 2026	The fourth month of dialysis
Coordination period	June 2026 through November 2028	30 months starting with the first month of eligibility
Medicare becomes primary	December 1, 2028	The month after month 30

If she had started home dialysis training in March and was expected to self-dialyze, eligibility would have begun March 1, 2026, and the period would end August 31, 2028. A transplant in September 2026 would not restart it; the same period runs.

In July 2026 her nephrologist bills the monthly capitation payment, 90960, at 420.00 to the plan. The plan allows 380.00, pays 304.00 and leaves 76.00 coinsurance; the 40.00 contractual adjustment is CO 45. The Medicare claim carries AMT D 304.00, CAS CO 45 40.00 and CAS PR 2 76.00 with insurance type 13. With a Medicare allowed amount of 372.75 (national, illustrative) and the deductible met, Medicare’s secondary payment is the lowest of three figures: its allowed amount minus the plan’s payment, 68.75; what it would have paid as primary, 298.20; and the amount the practice must accept as payment in full minus the plan’s payment, 76.00. Medicare pays 68.75, the remittance shows the plan’s 344.00 of payments and adjustments under OA-23, and Ms. Rivera owes 7.25.

Had the practice sent the July claim to Medicare first, it would have come back with CARC 22 and MA04 or, once Medicare’s record showed the plan, CARC 109.

What to do

• Put the eligibility date and the period end date on the account. Medicare becomes primary on the first of a month, and you can calculate that month on the day dialysis starts. Set a reminder a month ahead.
• Ask the Part III questions at every start of care and whenever the card changes. A job loss does not end the coordination period if COBRA continues; a new plan from a spouse starts primary billing to it.
• Build the Medicare claim from the plan’s remittance. Every CAS amount Medicare receives should match a line on the plan’s EOB, and the amounts should balance to the billed charge.
• Do not let the secondary claim wait on the plan. Medicare’s 12-month timely filing limit runs from the date of service even when Medicare is secondary.
• Denials to recognize: CARC 22 with MA04 or N4 means Medicare wants the primary’s identity or payment; resubmit with loop 2320 completed or the EOB attached. CARC 109 means Medicare’s record shows another payer is primary; bill the plan, or, if the record is wrong, have the patient call the BCRC and resubmit after the record is corrected. OA-23 on a paid secondary claim is not a denial; it is the prior payer’s impact and posts as an adjustment.
• Iridium Suite’s real-time eligibility check confirms the policy before the appointment, with demographics and policy data filled from the payer response.

Related terms

• Coordination of benefits
• Medicare crossover claims
• Group codes and reason codes on the remittance
• Timely filing limits
• EDI: the 837 and the 835
• Master the trick of Medicare secondary billing
• When does Medicare play second fiddle to a group health plan?
• The ESRD monthly capitation payment: 90951 to 90970
• Keep it simple: 3 ways to file secondary claims
• How to handle secondary insurance denials

Further reading: CMS: Medicare Secondary Payer rules for End-Stage Renal Disease (ESRD); Medicare Secondary Payer Manual, Chapter 2, section 20 (ESRD provisions, dual entitlement and COBRA); Medicare Secondary Payer Manual, Chapter 3, sections 20.2.1 and 30.5 (the questionnaire and the 837P loops); CMS MLN booklet MLN006903, Medicare Secondary Payer (July 2025); CMS Coordination of Benefits and Recovery contacts (BCRC).