Two numbers that don't fit together: American Samoa has just 9 Medicare-enrolled clinicians, and 8 of them refuse full assignment. That 88.9% rate is the highest of any U.S. state or territory, and it sits alongside New York's 10,909 non-assignment clinicians, the largest absolute count in the country. One is a rounding error in terms of workforce size. The other represents a city-sized cohort of providers who can legally bill Medicare patients above the approved rate. Together, they illustrate how non-assignment is both a structural problem and a geographic one.

Maryland and New York Lead the Contiguous States

Strip out the territories and the picture sharpens. Maryland ranks third overall, with 14.1% of its 34,093 Medicare-enrolled clinicians not fully accepting individual assignment, totaling 4,824 clinicians. New York follows at 10.5%, but its raw count of 10,909 non-assignment clinicians dwarfs every other state. For Medicare beneficiaries in these states, the practical consequence is straightforward: a meaningful share of providers can charge above the Medicare-approved amount, leaving patients responsible for the difference.

The Virgin Islands, at 18.6% non-assignment, sits between American Samoa and Maryland in rate terms. Guam comes in at 11.4%. The concentration of high non-assignment rates in the Mid-Atlantic and among territories suggests that local market conditions, not just provider preferences, shape these numbers.

Dentists and Mental Health Providers Carry the Highest Risk

Geography is only part of the story. Specialty-level data reveals where balance-billing risk is most acute, and the results should concern anyone tracking access to behavioral health and dental care.

Dentists have the highest non-assignment rate of any specialty: 68.2%, with 569 of 834 Medicare-enrolled dentists lacking either individual or group assignment. That rate is nearly three times the next comparable specialty. For Medicare beneficiaries who gained dental coverage under recent expansions, this means a large majority of enrolled dentists can bill beyond the approved rate.

Mental health counselors show a 23.3% non-assignment rate across 37,430 clinicians, and chiropractors sit just below at 23.1% across 38,016. These are not small specialties. At scale, rates in the low-to-mid twenties translate to tens of thousands of clinicians who can expose patients to unexpected costs.

Pediatric medicine's 24.1% rate nationally becomes even more pronounced in the top 10 non-assignment states, where 29.8% of pediatric medicine clinicians, 605 of 2,030, do not fully accept assignment. Pediatric Medicare enrollment is relatively narrow, covering children with disabilities and certain chronic conditions, which makes that rate particularly consequential for a population with limited provider alternatives.

Nurse Practitioners Dominate the Non-Assignment Count in High-Rate States

In the ten states with the highest non-assignment rates, Nurse Practitioners account for 16.39% of all non-assignment clinicians, the largest share of any specialty. That's 4,748 NPs out of 48,551 total enrolled in those states, a 9.78% non-assignment rate for the specialty in that subset.

The NP figure stands in contrast to mental health counselors in the same states, who post a 27.71% non-assignment rate. The counselors' rate is nearly three times higher, but NPs contribute more to the total non-assignment count simply because there are so many more of them enrolled. Pediatric medicine clinicians in the top 10 states have the highest specialty-level non-assignment rate at 29.8%, but their smaller total enrollment limits their share of the overall count.

What this means in practice: the states where Medicare beneficiaries face the most non-assignment exposure are not dominated by a single high-rate specialty. The problem is distributed across a wide range of provider types, from primary care NPs to behavioral health counselors to chiropractors. That distribution makes targeted interventions harder to design and harder to evaluate.

Given that Nurse Practitioners account for 16.39% of all non-assignment clinicians in the top 10 states, what market or credentialing dynamics are pulling this large and growing workforce away from full Medicare assignment?