NP or MD? Are we asking the wrong question

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By some accounts, NPs are one-third of the physician workforce. And in a battle raging between the two professions, the “scope of practice” of NPs has expanded over the years, threatening the moat physicians have created. Today, only about a third of NPs work in “primary care”; the rest are increasingly involved in specialty work – the poster child being care in the emergency department (ED), the subject of a new study.

That expansion raises an economic question as well as a professional one: does employing a lower-paid clinician produce lower-cost care?

For the bean counters, substituting NPs for MDs represents a significant economic efficiency; in many instances, one MD salary covers the cost of two NPs. For patients, more “providers,” irrespective of training, may cut wait times significantly. If the two interests are aligned, we have a win-win: lower cost and greater care – the epitome of the concept of value-added care. As it turns out, less expensive clinicians are not necessarily the bargain we anticipated.  

What the VA Emergency Department Can Tell Us

Emergency medicine, in general, has brought NPs into these “tip of the spear” roles, with 13% of ED care in the US delivered by NPs in 2019 and an almost identical proportion of NPs and MDs, 4% and 5% respectively, specializing in emergency medicine.  In 2016, the VA medical system granted NPs full practice authority, allowing them to treat patients independent of supervising physicians. Data from this experience formed the basis for the researcher’s analysis. 

Using 1.1 million visits over three years through 2020, the researchers asked a simple question: When patients are treated by nurse practitioners rather than physicians, what happens to resource use, outcomes, and the study's measures of clinical productivity?

The analysis accounted for patient characteristics, case complexity, and clinician experience. It then compared outcomes including ED length of stay and cost, hospital admission, 30-day mortality, and preventable hospitalization.

The Cheaper Clinician Isn't Always the Cheaper Car

Patients assigned to NPs had 11% longer ED stays and 7% higher ED costs. Their 30-day preventable hospitalization rate was also reported as 20% higher than the study mean. The researchers found no statistically significant difference in 30-day mortality and no overall difference in hospital admissions.

But the averages conceal several important nuances.

• Case complexity mattered. Differences in those outcomes shrank among healthier, less complex patients and grew with increasing severity. 
• Greater general and diagnosis-specific experience also reduced the NP-physician differences in length of stay and cost. The difference in 30-day preventable hospitalization, however, did not disappear with experience. 

Those patterns suggest that the difference may not simply be who holds which credential, but how clinicians respond when cases become difficult or uncertain.

When Uncertainty Uses Resources

One of the more revealing findings involved how NPs and physicians responded to diagnostic and treatment uncertainty.

NPs were more likely to seek additional information before making a decision. Compared with physicians, they increased their use of formal consultations with other providers, and of CT and X-ray imaging. The authors interpret this as greater reliance on external information when diagnostic certainty is lower. That additional information may improve decision-making, but it also consumes time and resources, which may help explain longer stays and higher ED costs. 

NP prescribing patterns were an even more interesting window into decision-making under uncertainty. The researchers examined opioids and antibiotics, two treatments for which different kinds of errors can carry significant costs. Because an unnecessary opioid prescription may cause harm, a cautious clinician may set a higher threshold for prescribing one; NPs prescribed opioids less often. For suspected infections, the researchers focused on the danger of failing to treat when antibiotics are actually needed. NPs appeared to respond by lowering that treatment threshold and prescribing antibiotics more often.

Despite prescribing fewer opioids, NPs' patients had similar subsequent rates of opioid use disorder. And despite receiving antibiotics more often, their patients were more likely to return to the ED with infections. Taken together with greater use of consultations and imaging, the findings suggest that productivity, as measured here, depends not only on the eventual clinical decision but also on how much information clinicians gather before making it and how they balance the risks of false-positive and false-negative decisions.

The study's most provocative finding emerges not from comparing NPs with physicians, but from comparing individual clinicians with one another. 

“NP vs. MD” May Be the Wrong Comparison

While physicians were more productive than NPs in this ED setting, the average difference between the two professions was relatively small compared with the variation within each profession. Variation among physicians and among NPs was roughly three times larger than the average difference between the professions. That produces substantial overlap between the two groups. The researchers estimate that a randomly selected NP would be less costly than a randomly selected physician about 38% of the time.

As it turns out, professional title appears to be an imperfect proxy for the combination of resource use and outcomes measured in this study. Credential strongly influences which patients clinicians are assigned, what roles they perform, and what they are paid, but it does not fully capture differences in individual performance.

Credentials contain incomplete information. If healthcare systems could measure individual performance more reliably, they might move toward matching the specific clinician to the specific clinical task at hand.

That possibility changes the staffing question from substitution to allocation: which clinician is best suited to which patient?

From Credential Substitution to Risk Matching

The opportunity for greater access and economic efficiency does not lie in simply substituting expensive physicians with lower-paid NPs. When researchers modeled 25% of VA emergency-department patients to NPs, non-wage spending rose by $197 million annually. But when NPs were “assigned” to the least-complex quarter of patients, the estimated net cost fell nearly sixfold, though it was still $29 million short of neutral. 

A lower-paid clinician does not necessarily produce lower-cost care, just as paying more for a clinician is not necessarily wasteful when better performance reduces downstream utilization or improves outcomes. The more useful question may therefore be not “Who is cheaper?” but “Who produces the best combination of outcomes and resource use for a patient at this level of risk?” Answering that question would require much better risk-stratified measures of individual-clinician performance. But if the substantial overlap between NP and physician performance found in this study is real, the larger efficiency gains may lie in matching patient risk to demonstrated clinician performance rather than relying on credentials alone.

Source: The Productivity Of Professions: Evidence From The Emergency Department, National Bureau of Economic Research Working Paper