Medicare and the Indian Health Service in South Dakota: Part D Is Forgiven, Part B Is Not

Sources: CMS, 2026 Medicare Parts A & B Premiums and Deductibles (fact sheet) and Medicare.gov, how to avoid Medicare penalties. The penalty is 10% for each full 12-month period you could have had Part B and did not, and it lasts as long as you have Part B.

What South Dakota's own Medicare data shows

CMS publishes county-level Medicare enrollment, including how many beneficiaries have Part A only. Statewide, 7.7% of South Dakota's 205,238 Medicare beneficiaries lack Part B. In the counties covering the state's largest reservations, the number is dramatically higher.

Share of Medicare beneficiaries with Part A but no Part B. Source: CMS Medicare Monthly Enrollment (county level, through March 2026), March 2026.

The full county picture, ordered by American Indian share of Medicare beneficiaries:

Source: CMS Medicare Monthly Enrollment (county level, through March 2026), March 2026. CMS records race administratively rather than by self-identification, so American Indian counts here should be read as a floor, not a census.

Two patterns stand out, and they point in opposite directions. Part D enrollment runs low in the highest AI/AN counties, 46.3% in Oglala Lakota County against 76.8% statewide. That is a rational response to a real rule: IHS pharmacy is creditable coverage, so skipping Part D carries no penalty. Part A only enrollment runs high, and that one has no such protection behind it.

Be careful with the causation here, and we will be too. Some people with Part A only have employer coverage or other good reasons. What the data supports is that beneficiaries in these counties are far more likely to be enrolled in Part A alone, not that any particular person has been penalized.

The consequence nobody mentions: Purchased/Referred Care

Purchased/Referred Care is not walking into your clinic. It is IHS paying an outside provider for care the local facility cannot deliver, which in practice means specialists, surgery, and advanced imaging. It is budget-limited, and IHS states plainly that "the Indian Health Service is not an entitlement program, and therefore funding for PRC is not guaranteed by the Federal government."

PRC is also conditioned on using your other coverage. The Indian Health Manual states that an individual is required to apply for an alternate resource where one reasonably may exist, and that "refusal to apply for alternate resources when there is a reasonable possibility that one exists, or refusal to use an alternate resource, requires the denial of eligibility for PRC." IHS names Medicare Part A and Part B among those resources.

What tribal members actually get, stated precisely

There is a persistent belief that being an enrolled tribal member changes what Medicare costs. It does not. There is no AI/AN exemption from the Part B premium, the Part B deductible, Part A or Part B coinsurance, Part D costs, or IRMAA, and no AI/AN Special Enrollment Period.

The real cost-sharing protections people are thinking of come from Medicaid and CHIP rules and from Marketplace rules. CMS scopes them carefully in its own tribal materials, repeating the phrase "in Medicaid and the Children's Health Insurance Program" every time. Those are genuine and valuable protections. They are simply not Medicare.

What you do get is three separate things, worth naming separately:

1. At an I/T/U facility: IHS waives the Medicare deductible and coinsurance. A provider waiver, not a Medicare exemption, and it does not follow you elsewhere.
2. At an I/T/U pharmacy: drugs at no cost to you, and IHS counts as creditable Part D coverage.
3. Through Medicaid or a Medicare Savings Program: the statutory cost-sharing protections, which require actually enrolling.

Because these get garbled so often, here they are as claim and reality:

Sources: 42 C.F.R. 423.56, 42 C.F.R. 407.20, 42 C.F.R. 447.56, CMS Claims Processing Manual Ch. 19, Indian Health Manual Part 2 Ch. 3, and SSA POMS SI 00830.830.

The programs that genuinely lower your costs

If you want your Medicare costs reduced, these are the levers that actually exist.

Medicare Savings Programs. South Dakota's 2026 limits are $1,816 in monthly income for an individual and $2,455 for a couple, with resource limits of $9,950 and $14,910. The state says the program can save a beneficiary up to $2,424 a year. QMB, the broadest tier, pays your premiums and bars providers from billing you Medicare deductibles and coinsurance. Critically, an MSP is also one of the only two ways to escape a Part B late enrollment penalty. If you delayed Part B and your income is low, this is both premium help and penalty relief in one application.

Extra Help for Part D. Income limits are $23,940 for an individual and $32,460 for a married couple. Medicare.gov lists a resource limit of $18,090 for an individual, which includes an allowance for burial expenses; SSA's base figure without that allowance is $16,590. Extra Help also waives the Part D late enrollment penalty while you have it. Qualifying for an MSP qualifies you automatically.

One warning on income counting. Certain Indian trust payments are excluded from income and resources for these determinations, including per capita distributions of funds held in trust by the Secretary of the Interior and up to $2,000 a year from individual interests in trust or restricted lands. Tribal gaming per capita distributions are not on that exclusion list. Assuming they are can cost someone their eligibility, so bring your actual distribution paperwork when you apply.

Why your clinic wants you enrolled in Medicaid too. When a Medicaid-eligible AI/AN patient receives services through an IHS or tribal facility, the federal government reimburses the state at 100%. As CMS puts it, those services "cost your state nothing." Enrolling routes outside money into your local facility rather than draining its budget.

D-SNPs: approved everywhere, enrolled almost nowhere

Dual Eligible Special Needs Plans are built for people who have both Medicare and Medicaid, and dual eligibility runs high in reservation counties, from 11.6% up to 33.4%, against 9.7% statewide.

All 4 South Dakota D-SNPs are approved to operate in all 66 counties, including every reservation county. What is missing is not availability. It is enrollment.

Source: CMS Medicare Advantage Enrollment by Contract, Plan, State and County (July 2026) and CMS Medicare Advantage Contract Service Area file (July 2026). CMS suppresses counts of 10 or fewer for privacy.

Pine Ridge, Rosebud, Bennett, and Mellette had no D-SNP enrollees at all in any of the four plans. We are not going to speculate about why, because no federal source establishes a cause. What we can say is that the plans are approved there and someone in those counties who is dually eligible may have an option they have never been shown.

Two details to carry into any conversation about these plans. All four South Dakota D-SNPs are Coordination-Only, meaning Medicare and Medicaid stay separately administered even inside the plan; South Dakota has no fully or highly integrated dual plan. And CMS labels one carrier's plans as serving "select counties," so plan-level service areas can be narrower than the contract. Check your own ZIP on Medicare's Plan Finder rather than trusting any statewide claim, including ours.

Can a tribe pay your premiums?

Sometimes, and CMS confirms that some tribes do. The authority is not a tribe-specific Medicare provision, because none exists. It is the general third-party payer rule: 42 C.F.R. 408.80(a) permits "an employer, a lodge, union, or other organization" to pay Part B premiums for one or more enrollees, and SSA's own manual notes this does not require agency approval. CMS told tribal audiences directly in a December 2024 webinar that some tribes pay Medicare premiums for members, calling it sponsorship, and that some run Part D sponsorship programs.

Then comes the limit that decides the practical answer. Group payment cannot be made for enrollees whose premiums are deducted from their monthly Social Security benefit or paid by the state under a buy-in agreement. Most beneficiaries have Part B withheld from Social Security, and everyone in QMB, SLMB, or QI has Part B paid by South Dakota under buy-in. Both groups are excluded.

So the hierarchy is simple. If you qualify for a Medicare Savings Program, that is the answer: it pays the premium, it erases the Part B penalty, and it costs the tribe nothing. Tribal Part B sponsorship only reaches someone who pays their premium directly and is not in an MSP. Ask your Indian health care provider or tribal benefits coordinator what your tribe actually offers, since the documented programs are mostly Part D.

Why the stakes are higher here

The enrollment gap lands on the population that can least absorb it. Life expectancy at birth for American Indian and Alaska Native people was 70.1 years in 2023, against 78.4 for white non-Hispanic Americans, using NCHS tables adjusted for race misclassification on death certificates.

Among Medicare fee-for-service beneficiaries aged 67 and older, 42.3% of AI/AN beneficiaries had diagnosed diabetes in 2023, against 24.7% of white non-Hispanic beneficiaries. In South Dakota specifically:

Source: CDC Chronic Disease Indicators. Life expectancy from NCHS United States Life Tables, 2023 (NVSR Vol. 74 No. 6, misclassification-adjusted); diabetes prevalence from CDC US Diabetes Surveillance System, diagnosed diabetes, Medicare fee-for-service 67+.

Diabetes and heart disease are exactly the conditions that generate specialist referrals, infusions, and surgeries: the care that lands outside the clinic, where Part B pays and the IHS waiver does not reach.

What to watch for 2027

1. Your Part D creditable coverage letter. IHS no longer mails these annually. Request one from your service unit when you enroll, and keep it.
2. The loss-of-Medicaid Special Enrollment Period. With dual eligibility at 33.4% in some counties, this matters: losing Medicaid lets you enroll in Part A and Part B without a late enrollment penalty.
3. D-SNP enrollment on the reservations. Four counties sit at zero today. If that changes, it will show up in the CMS monthly enrollment file first.
4. The high-cost drug add-on for I/T/U hospitals continues in CY2026 under the outpatient payment rule, which protects reimbursement when a Medicare-enrolled member gets an expensive drug at a tribal hospital.
5. The scope of 100% federal matching for services received through I/T/U facilities. CMS has an open request for comment on how "received through" is defined, so treat current guidance as live rather than settled.

How we know all this: Big Sioux Benefits runs every article through a data desk that cross-references CMS enrollment and plan files, the CMS Medicare Claims Processing Manual, the Indian Health Manual, SSA program rules, and CDC and NCHS health statistics, built by Strategic AI Architects. Every figure here comes from a public federal source, linked above. Where federal guidance is unsettled, we said so instead of filling the gap. This is education, not advice, and it is not legal or tax guidance. Confirm your own eligibility and costs with a licensed agent, your Indian health care provider or tribal benefits coordinator, Medicare.gov, or South Dakota DSS. We take no payment from any carrier to feature a plan.