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Provider Type and Management of Common Visits in Primary Care

Douglas W. Roblin, PhD; Hangsheng Liu, PhD; Lee F. Cromwell, MS; Michael Robbins, PhD; Brandi E. Robinson, MPH; David Auerbach, PhD; and Ateev Mehrotra, MD, MPH
In primary care, nurse practitioners and physician assistants do not necessarily order more ancillary services, or more costly services among alternatives, than physicians.
Table 1 displays patient characteristics on visits for N/B pain or ARI. Compared with PCPs, patients on N/B pain or ARI visits attended by NPs/PAs were younger, of shorter enrollment duration, and had lower prevalence of major comorbidities.

Table 2 displays the percent of N/B pain visits with orders for diagnostic radiology services and prescription medications by provider type, both before and after propensity score matching. After propensity score matching, PCPs were more likely to order an N/B-related CT/MRI (3.3% vs 2.1%; P <.01) or a narcotic analgesic (30.1% vs 26.9%; P <.01). On the other hand, NPs/PAs were more likely to order a nonnarcotic analgesic (13.5% vs 8.5%; P <.01) or a musculoskeletal relaxant (45.8% vs 42.5%; P <.01). N/B pain visits with an order for an x-ray did not differ between NPs/PAs or PCPs (21.6% vs 22.1%; P = .53).

Table 3 displays the percent of ARI visits with orders for diagnostic radiology services and prescription medications by provider type, both before and after propensity score matching. After propensity score matching, there were significant differences in practice between NPs/PAs and PCPs in treatment of ARI. Over all visits, PCPs were more likely to order ARI-related x-rays (8.6% vs 6.3%; P <.01), CTs/MRIs (0.5% vs 0.3%; P <.01), a broad-spectrum antibiotic (42.5% vs 41.5%; P = .03), or a rapid strep test (9.7% vs 6.3%; P <.01). NPs/PAs, however, were more likely to order any antibiotic (73.7% vs 65.8%; P <.01). As with N/B pain visits, this difference in practice variation between NPs/PAs and PCPs was the same as that observed before propensity score matching.

In the first sensitivity analysis, matching on a smaller caliper made no difference in the findings. Next, the practice pattern differences between NPs/PAs and PCPs over all visits on which a diagnosis of N/B pain (or ARI) was suggested were basically the same whether the relevant ICD-9-CM code was primary or secondary (Tables 2 and 3). Finally, there was some clustering by provider, and adjusting for this clustering tended to push the statistical significance of the NP/PA versus PCP effect toward the null (eAppendix B) in some cases; for example, CT/MRI for back pain pushing significance to nonsignificance (ie, P >.05). For most comparisons by provider type, however, the NP/PA versus PCP effect was significant whether the model did or did not account for clustering of service orders by provider.

DISCUSSION

The objective of our study was to ascertain whether NPs/PAs differed from PCPs in frequency of orders for diagnostic services or prescription medications when managing adults presenting with N/B pain or ARI in primary care. We used propensity score matching of visits to adjust for the fact that patients attended by NPs/PAs tended to be younger and have a lower prevalence of comorbidities, which could affect diagnostic or therapeutic treatment choice.

After matching, several important differences by type of primary care provider were noted in management of N/B pain: PCPs were more likely to order CTs/MRIs and narcotic analgesics and NPs/PAs were more likely to order nonnarcotic analgesics and muscle relaxants. Similarly, differences were noted in management of ARI: PCPs were more likely to order CTs/MRIs—although the rate of these orders was low—as well as x-rays, broad spectrum antibiotics, and rapid strep tests; NPs/PAs were more likely to order any antibiotic. Thus, on balance, PCPs tended to be more likely than NPs/PAs to order diagnostic or therapeutic services related to N/B pain and ARI visits and to order more costly services among alternatives (eg, CTs/MRIs vs x-rays for adults with N/B pain, broad spectrum antibiotics vs first-line general antibiotics for adults with ARIs).

Evidence from this health maintenance organization (HMO), therefore, differs from the results of other studies, suggesting that NPs/PAs might more frequently order diagnostic or therapeutic services for common conditions treated in primary care; or, among alternatives, order more costly services.27 Our study’s findings are, however, consistent with another recent study using data from the National Ambulatory Medical Care Survey (NAMCS), which found no significant differences between NPs/PAs and physicians in office-based practice when ordering “low-value” ancillary services.16 In our study, the pattern of ancillary services use suggests that NPs/PAs might have been more judicious in use of “low-value” ancillary services than PCPs. For management of back pain, overuse of CTs/MRIs and narcotic analgesics is a current concern.32 We found NPs/PAs had lower rates of use of CTs/MRIs and narcotic analgesics in management of N/B pain. In management of an ARI, overuse of antibiotics—particularly broad-spectrum antibiotics—is a long-standing concern.33-36,38 Overuse of rapid strep tests is another concern in management of ARIs,37 and we found NPs/PAs were less likely to order broad-spectrum antibiotics and rapid strep tests.

What factors might have contributed to this NPs/PA practice pattern? Training of NPs/PAs typically emphasizes patient education and self-management over other interventional strategies. Thus, NPs/PAs may be more comfortable in initially managing N/B pain or ARI with fewer ancillary services. It is also possible that NPs/PAs are more compliant than PCPs with clinical practice guidelines in management of N/B pain or ARI in primary care.

Sensitivity analyses suggest this study’s findings are robust. Matching a narrower caliper —one a tenth of that used for the findings discussed in this paper—yielded similar results. Frequencies of orders by NPs/PAs versus PCPs for visits related to N/B pain (or ARI) did not generally differ by whether N/B pain (or ARI) was indicated as a primary or secondary diagnosis. The clustering analyses do indicate some proportion in outcomes by provider type is due to practice variation among individual providers; however, the persistence of significance of the NP/PA effect after adjusting for provider clustering strongly suggests that practice variation by provider type is important.

Limitations

Our study was conducted within the context of a single, group-model HMO in the southeastern United States. Because this HMO had a strong tradition encouraging multidisciplinary, collaborative primary care, study findings might not be generalizable to other settings with a different delivery model. NPs/PAs work under supervision of PCPs; however, we had no measure of how supervision practices might have influenced NP/PA ordering patterns. During the study period, NPs/PAs were relatively established in this HMO; their practice patterns might not represent practice patterns of newly hired NPs/PAs. This HMO had relatively well-defined practice guidelines for management of N/B pain and ARI. Rates of orders for medications reflect only orders for prescriptions and not over-the-counter medications. We did not investigate specific quality measures, so we cannot conclude that over- or underuse of specific diagnostic services or prescribed medications was beneficial or detrimental to patient health. The propensity score matching relied on a limited number of patient covariates, and does not necessarily account for illness acuity within the selected comorbidities. Other factors that varied across clinics where NPs/PAs practiced (eg, use of care managers in some clinics but not others) might also influence practice variation by provider type.

Other factors that we did not consider in our analyses could offset the potential savings in medical care delivery costs due to lower ancillary services rates on visits attended by NPs/PAs. Length of visit was not available, so we could not assess if longer NP/PA visits decreased visit productivity (in terms of visits per day) and attenuated labor cost savings due to lower NP/PA salaries.13,45 We did not examine variation by provider type in other utilization measures such as referrals or potentially avoidable hospital admissions. Other studies that have examined postvisit utilization generally find equal or lower rates of these classes of services following NP/PA visits compared with physician visits.15,22 Similarly, we show elsewhere that the extent of NP/PA integration into this HMO’s primary care delivery system did not increase levels of these broad classes of utilization across all medical conditions.39

CONCLUSIONS

In this group model HMO, NPs/PAs who attended visits related to N/B pain or ARI in adult primary care typically had lower rates of associated orders for diagnostic services or prescription medications than PCPs when treating patients of comparable age, gender, and comorbidities. 

Author Affiliations: School of Public Health, Georgia State University (DWR), Atlanta, GA; Center for Clinical and Outcomes Research, Kaiser Permanente (DWR, LFC, BER), Atlanta, GA; RAND Corporation (HL, MR, AM), Santa Monica, CA; Harvard University (HL, AM), Cambridge, MA; Massachusetts Health Policy Commission (DA), Boston, MA.

Source of Funding: Funds to conduct this study were provided by a grant from the American Academy of Family Physicians. The funding source had no role in the study design, data collection, interpretation of the results, and decision to submit the manuscript. Analyses and interpretations presented in this manuscript are solely those of the authors and do not represent the views of the sponsor or the authors’ employers.

Author Disclosures: The authors report no relationship or financial interest with any entity that would pose a conflict of interest with the subject matter of this article.

Authorship Information: Concept and design (DWR, HL, MR, DA, AM); acquisition of data (DWR, LFC, DA); analysis and interpretation of data (DWR, HL, LFC, MR); drafting of the manuscript (DWR, MR); critical revision of the manuscript for important intellectual content (DWR, HL, MR, BER, AM); statistical analysis (DWR, LFC, MR); provision of patients or study materials (BER); obtaining funding (DWR, DA); administrative, technical, or logistic support (BER, AM); and supervision (DWR).

Address Correspondence to: Douglas W. Roblin, PhD, School of Public Health, Georgia State University, 1 Park Pl, Rm 662C, Atlanta, GA 30303. E-mail: DRoblin@gsu.edu. 
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