Medicare, the federal health insurance program for people aged 65 or older and certain younger people with disabilities, provides health coverage regardless of a person’s medical history. Unlike many private insurance plans before the Affordable Care Act, Original Medicare does not use medical underwriting to determine eligibility or set premiums. If an individual meets the program’s age or disability requirements, they are entitled to coverage. Having a pre-existing condition (PEC), such as heart disease, cancer, or diabetes, will not prevent enrollment in the program.
Original Medicare Coverage (Parts A and B)
Original Medicare, consisting of Part A (Hospital Insurance) and Part B (Medical Insurance), covers services for pre-existing conditions immediately upon enrollment. Enrollment is guaranteed for eligible individuals, meaning the federal government cannot deny coverage based on current health status or a chronic illness diagnosis.
Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health services, and is premium-free for most people who have paid Medicare taxes for at least 10 years. Part B covers doctor visits, outpatient care, durable medical equipment, and preventive services, and requires a standard monthly premium. Part B premiums are not adjusted based on health conditions, though they can be higher for beneficiaries with higher incomes.
Treatment for a PEC is covered the same way as treatment for any new medical concern. For instance, a person with an existing diagnosis of rheumatoid arthritis will have specialist visits and infusions covered under Part B, subject to standard deductibles and coinsurance. The program treats all medically necessary care equally, ensuring a prior diagnosis does not lead to exclusion from coverage.
Enrollment in Private Plans (Medicare Advantage and Part D)
Private insurance plans that contract with the government, specifically Medicare Advantage (Part C) and Part D (Prescription Drug Coverage), must accept individuals with pre-existing conditions. Medicare Advantage plans, which bundle Part A, Part B, and often Part D coverage, cannot deny enrollment to any eligible beneficiary residing in the plan’s service area. This ensures a person with a PEC can choose an Advantage plan over Original Medicare.
Part D plans, which provide stand-alone prescription drug coverage, also operate under a guaranteed issue rule and cannot deny enrollment based on a person’s health status or the medications they require. Management of pre-existing conditions in these private plans is handled through the plan’s structure, not enrollment denial. Advantage plans may use specific provider networks, require prior authorization for certain services, or limit specialist access, which can affect care for a chronic condition.
For Part D, the plan’s formulary (its list of covered drugs) dictates which medications for a PEC are covered and the cost-sharing level. While the plan must cover a minimum number of drugs in most therapeutic categories, a specific brand-name drug for a condition like multiple sclerosis may be placed on a higher cost-sharing tier. While enrollment is guaranteed, the specifics of how a PEC is covered—including network access and drug costs—can vary significantly between private plans.
Supplemental Coverage and Underwriting (Medigap)
Medicare Supplement Insurance, or Medigap, is the one area where pre-existing conditions can directly impact access and coverage. Medigap policies are sold by private companies to cover the “gaps” in Original Medicare, such as deductibles, copayments, and coinsurance. Because these policies are not primary coverage, their underwriting rules differ from the guaranteed issue rules of Original Medicare and Medicare Advantage.
The most protected time to enroll in Medigap is during the one-time, six-month Medigap Open Enrollment Period (OEP), which begins when a beneficiary is 65 or older and enrolled in Part B. During this OEP, insurers must sell the applicant any policy they offer, cannot use medical underwriting, and cannot charge higher premiums or deny coverage based on any health condition. This guaranteed issue right is the only time an individual with a PEC is guaranteed a Medigap policy.
Outside of this specific OEP or other limited guaranteed issue situations, Medigap insurers are legally permitted to use medical underwriting. This means an applicant must answer health questions, and the insurer can review their medical records before issuing a policy. If a person applies outside the OEP and has a significant PEC, the insurer may deny the application entirely.
If a policy is issued outside a guaranteed issue period, the insurer may impose a pre-existing condition waiting period of up to six months. During this period, the Medigap policy will not pay for out-of-pocket costs related to any condition treated in the six months prior to the policy start date. However, an applicant can reduce or eliminate this six-month waiting period by showing proof of prior “creditable coverage,” such as a former employer health plan. If the applicant had at least six months of continuous creditable coverage before applying for Medigap, the six-month waiting period must be waived completely.