"uh" modifier on the medicaid pricing schedule

Assuming UH is a typo as level 12 is UC, modifiers U1 U9 & UA- UD are modifiers set aside for assignment at the state level by Medicaid agencies. Each state uses U modifiers differently so without knowing what state it's going to be hard to say what the modifier code is actually used for. Not only can U(1-D) mean different things in different state, they can also mean different things under different sub grouping's of HCPS codes (13 modifiers is not enough from what I can see in dealing with NY Medicaid)

For some history behind the codes, I can tell you that many years ago there were local HCPCS codes (beginning with X-Z). If a HCPCS/CPT code did not exist to describe a service or situation, the payers could make one up. Under HIPAA administrative simplification, there was a requirement to use national code sets so local codes were retired. This led to the creation of the special modifiers to allow for made up codes under the national HCPCS level II code set.
Heres what I can find.

The UC modifier should be added to the observation claim line if the service is being provided in a discrete observation unit (established in compliance with 10 NYCRR 405.19 (g)). Facilities will be reimbursed an enhanced hourly rate (i.e., 20 percent higher) for providing observation in designated units if they code the UC modifier. However, observation services provided in non-designated units (i.e., "scattered site beds") should be coded using G0378 without the UC modifier.