In new article just published by the journal Current Problems in Diagnostic Radiology, a research team from the Harvey L. Neiman Health Policy Institute follows up on their prior work measuring the extent of utilization of non-physician practitioners (NPPs) - specifically nurse practitioners (NPs) and physician assistants (PAs) - employed by U.S. radiology practices. This latest study was not limited to use of NPPs by radiology practices. The study assessed broadly the growth of diagnostic imaging billed by NPPs across the United States, finding an increase in the rates of diagnostic imaging studies interpreted by NPPs. Of note, the authors document the surprising, and concerning, increase in NPP imaging interpretation of advanced imaging studies such as CT and MRI. 

This was a retrospective study using patient claims for diagnostic imaging studies performed between 2016 and 2020 from Optum's Clinformatics Data Mart The data was modeled to determine the likelihood of patients receiving NPP-interpreted vs physician-interpreted imaging. The rates and trends in proportions of NPP-billed claims for interpretation services were then assessed based on urban versus rural settings, as well as differing state scope-of-practice (SOP) regulations and legislation.

Over 110 million diagnostic imaging claims were reviewed with most (97%) attributed to physician interpretation services. But looking at NPP-billed imaging interpretation claims, the highest share of diagnostic imaging interpreted by NPPs occurred in 2020 (3.3%), up from 2.6% in 2016, a 26.9% increase over that time span. Of the imaging studies interpreted by NPPs, 79.4% were either radiography/fluoroscopy (53.3%) or ultrasound (26.1%).

In their evaluation of diagnostic imaging of state-level NPP practice authority, researchers observed increases in both metropolitan and micropolitan areas when comparing states with more restrictive NPP scope of practice laws to states with more moderate laws. But those states with more moderate scope of practice laws saw the larger increases in rates of imaging interpretations by NPPS.

The most surprising finding to me was the extent of computed tomography and magnetic resonance advanced imaging (CT and MRI) interpretation services found to be performed by NPPs. A 2019 American Journal of Roentgenology reported that non-advanced imaging (i.e., radiography/fluoroscopy) accounted for 94% of NPP imaging interpretation. A study of NPPs working in radiology-only practices published earlier this year by the Journal of the American College of Radiology -- also the work of a research team from the Harvey L. Neiman Health Policy Institute -- found that bone densitometry and swallowing studies accounted for 87% of NPP-billed imaging. The new study found that NPP interpretation activity was somewhat focused on radiography/fluoroscopy (53%) and ultrasound (24%).  But surprisingly, the combined percentage CT and MRI made up of 21% of the overall NPP-interpreted imaging. 

As noted above, the authors, correctly in my view, express concern over the extent of NPP imaging interpretation of advanced imaging studies, given NPPs' deficiencies in imaging training.

One can expect ongoing research in the extent to which NPPs are performing radiology services. Some of this is alarming, but some has to be expected given the manpower shortages among physician specialties, including radiology.

I hope that researchers will also turn their attention to tracking the utilization of NPPs in the supervision of diagnostic imaging tests that require administration of contrast. Both Medicare rules and ACR's practice parameters accept NPP supervision of Level 2 tests to the extent permitted by a state's rules and the NPP's state scope of practice regulations.