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The American Journal of Managed Care April 2017
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Provider Type and Management of Common Visits in Primary Care
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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.
Objectives: Debate continues on whether nurse practitioners (NPs) and physician assistants (PAs) are more likely to order ancillary services, or order more costly services among alternatives, than primary care physicians (PCPs). We compared prescription medication and diagnostic service orders associated with NP/PA versus PCP visits for management of neck or back (N/B) pain or acute respiratory infection (ARI).

Study Design: Retrospective, observational study of visits from January 2006 through March 2008 in the adult primary care practice of Kaiser Permanente in Atlanta, Georgia.

Methods: Data were obtained from electronic health records. NP/PA and PCP visits for N/B pain or ARI were propensity score matched on patient age, gender, and comorbidities.

Results: On propensity score-matched N/B pain visits (n = 6724), NP/PAs were less likely than PCPs to order a computed tomography (CT)/magnetic resonance image (MRI) scan (2.1% vs 3.3%, respectively) or narcotic analgesic (26.9% vs 28.5%) and more likely to order a nonnarcotic analgesic (13.5% vs 8.5%) or muscle relaxant (45.8% vs 42.5%) (all P ≤.05). On propensity score-matched ARI visits (n = 24,190), NP/PAs were more likely than PCPs to order any antibiotic medication (73.7% vs 65.8%), but less likely to order an x-ray (6.3% vs 8.6%), broad-spectrum antibiotic (41.5% vs 42.5%), or rapid strep test (6.3% vs 9.7%) (all P ≤.05).

Conclusions: In the multidisciplinary primary care practice of this health maintenance organization, NP/PAs attending visits for N/B pain or ARI were less likely than PCPs to order advanced diagnostic radiology imaging services, to prescribe narcotic analgesics, and/or to prescribe broad-spectrum antibiotics.

Am J Manag Care. 2017;23(4):225-231
Takeaway Points

Practice variation by providers, rather than by provider type, may be more important in understanding differences in management of conditions commonly presented in primary care.

Nevertheless, concerns have been expressed that nurse practitioners (NPs) and physician assistants (PAs) might more frequently order ancillary services, or more costly services among alternatives, compared with primary care physicians. In this study of a group model health maintenance organization’s primary care practice, we found NPs and PAs were less likely to order: 
  • Advanced diagnostic imaging or narcotic analgesics for management of neck or back pain. 
  • Broad-spectrum antibiotics or rapid strep tests for management of acute respiratory infections.
Increasing the percentage of nurse practitioners (NPs) and physician assistants (PAs) in the primary care provider workforce has been suggested as one strategy for addressing the United States’ national shortage of primary care physicians (PCPs).1-5 Although NPs/PAs have clinical training and regulated scopes of practice that differ from those of PCPs, they are permitted to manage a range of medical conditions in ambulatory care.6-11 A recent survey of the US national population indicated broad acceptance of NPs/PAs as primary care providers.12

Currently, there is interest in how the addition of NPs/PAs to primary care might impact patient outcomes, medical service utilization, and costs.13-17 Prior studies have been relatively consistent in demonstrating that levels of patient satisfaction with care and quality of care are similar between NPs/PAs and physicians11,18-23; however, it is less clear whether care provided by NPs/PAs or PCPs affects medical services use and cost.

An NP/PA visit can be cost saving compared with a PCP visit because salary differentials lower the cost of time for patient evaluation and management.13,17,24,25 However, this cost advantage may be offset if NPs/PAs order ancillary services (ie, laboratory, radiology, pharmacy) at higher rates than PCPs, or order more costly services among alternatives (eg, computed tomography [CT] scan/magnetic resonance image [MRI] vs x-ray).

Studies show mixed results on use of ancillary services by provider type. One study found NPs/PAs ordered significantly more CTs/MRIs for primary care visits than physicians treating Medicare patients26; another found no difference in office-based care using the National Ambulatory Medical Care Survey (NAMCS).16 A study of Veterans Affairs patients with lower back pain found no statistically significant difference in clinical appropriateness of lumbar spine MRIs by provider type (physician, PA, or NP).27 In prescribing medications, rates of prescribing controlled medications28 and antibiotics16,29 were similar for NPs, PAs, and physicians.

The primary question of our retrospective observational study was: Do NPs/PAs attending visits for neck or back (N/B) pain or acute respiratory infection (ARI) in primary care order ancillary services at different rates than PCPs? We focused on these 2 medical conditions for several reasons. Musculoskeletal pain and respiratory infections are common reasons that adults present for medical care in the United States,30 and visits for N/B pain or ARI are frequently accompanied by orders for ancillary services. There are general concerns that, across all providers, certain types of ancillary services are overused and add cost without value—specifically, CTs/MRIs and narcotic analgesics in management of N/B pain,16,31,32 and antibiotics (particularly broad-spectrum antibiotics) in management of ARI.33-38


Study Setting and Period

At the time of this study, Kaiser Permanente Georgia (KPGA) provided comprehensive medical services to approximately 240,000 enrollees per year (59% Caucasian, 33% African American) in the Atlanta area. The study protocol was reviewed, approved, and monitored by the KPGA Institutional Review Board.

During the 27-month study period (January 2006 through March 2008), approximately 180,000 KPGA members were empaneled to a PCP in the Adult Medicine department. The study period is limited to these 27 months because, beginning in 2006, an electronic health record (EHR) system was fully implemented—allowing for measurement of providers’ orders for medical services—and it ends in early 2008 when the multidisciplinary Adult Medicine department became a PCP-only department.39 More recent comparisons of practice variation are not available.

Sample Definition

The sample used for analysis consisted of patients 18 years or older at the time of presentation for an “incident” N/B pain or ARI visit in the KPGA Adult Medicine department. An “incident” visit was considered to have occurred if the patient who presented for N/B pain or ARI had no visit in adult ambulatory medicine for N/B pain or ARI, respectively, for at least a period of 30 days prior to the visit. Using this definition, a single patient may have had multiple incident visits during the study period.

A visit for N/B pain or ARI was determined from specific International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis codes associated with the visit, either designated as a primary or secondary condition (eAppendix A [eAppendices available at]). Due to the broad range of ARIs, we selected specific ICD-9-CM diagnosis codes used in previously published studies as indicative of an ARI.33-38

Research Design

We used propensity score matching of visits to reduce the effect of patient selection on comparisons of practice variation between NPs/PAs and PCPs when attending a visit for N/B pain or ARI. NPs/PAs tend to treat younger, healthier patients than physicians which, in turn, can affect rates and mix of ancillary service orders.11,16,40 Thus, we propensity score-matched NP/PA visits with PCP visits on preexisting patient characteristics to address potential selection issues.

Separate analyses were conducted for N/B pain and ARI visits. First, within each visit class, the propensity for a visit to be attended by a NP/PA

versus PCP was estimated with logistic regression.41-43 Second, based on the estimated propensity of NP/PA versus PCP attending a visit, each N/B pain or ARI visit attended by an NP/PA was matched with an N/B pain or ARI visit, respectively, attended by a PCP.


All analyses used computerized administrative and EHR databases. Records were linked by unique identifiers and sequenced by event dates. The EHR databases distinguished services ordered by the provider from services completed by the patient. We used services ordered rather than services delivered because rates of services delivered can be affected by factors such as patient access (eg, limited locations for CT/MRI services) or cost sharing (eg, co-payments for prescription medicines).44 Thus, services ordered are more representative of practice style than services delivered.

Services ordered at the time of the visit were linked to the incident N/B pain or ARI visit by unique visit numbers. All services ordered were attributed to the provider attending the visit. Thus, there is no attribution of orders by an NP/PA to a PCP providing practice supervision (as might occur in billing of “incidental to” visits).

We were advised by several senior physicians that some orders related to the incident visit might occur up to 3 to 5 days following conveyance to the attending provider of initial tests or consultation results. Thus, we considered a diagnostic service order or prescription order as related to the incident visit if it occurred within 5 days from the visit date and was ordered by a provider in the adult primary care department at the same primary care facility where the incident visit occurred. Follow-up orders occurred in less than 5% of NP/PA visits and/or PCP visits for either N/B pain or ARI (data available on request).


Dependent variables. The outcomes of interest were the percentages of visits associated with an order for a specific service class. The service order classes defined for N/B pain visits were: N/B x-rays, N/B CTs/MRIs, nonnarcotic analgesic prescriptions, narcotic analgesic prescriptions, and prescriptions for skeletal muscle relaxants. The service order classes defined for ARI visits were: ARI x-rays, ARI CTs/MRIs, rapid strep tests, any systemic antibiotic prescription, any broad-spectrum antibiotic prescription, and any prescription for relief of ARI symptoms (eg, decongestants, expectorants, respiratory system anti-inflammatory medications). We combined CTs with MRIs because preliminary review of the data indicated very low rates of MRIs relative to CTs, and availability of one or the other of these advanced diagnostic imaging services at selected facilities preferred by a patient might have affected a provider’s decision to schedule one or the other of these services.

Independent variable. The primary independent variable was the type of provider who attended the visit: NP/PA versus PCP.

Patient covariates. Covariates were: age at the time of the visit, gender, years of enrollment with KPGA at the time of the visit, and the presence (vs absence) of several major comorbidities (diabetes, hypertension, hyperlipidemia, cardiovascular disease [coronary artery disease, congestive heart failure, cerebrovascular disease], asthma or chronic obstructive pulmonary disease, or cancer) at the time of the visit.

Statistical Analysis

The initial step in analysis was to compare the distribution of patient characteristics at presentation for a visit for N/B pain or ARI with respect to attending provider type: NP/PA versus PCP. Independence of patient characteristics from attending provider type (ie, NP/PA vs PCP) was assessed using a χ2 test.

Propensity of a visit for N/B pain or ARI to have been attended by an NP/PA versus PCP was estimated using logistic regression including the patient covariates. This step resulted in a probability estimate of NP/PA versus PCP selection. Matching of 1 NP/PA visit with 1 PCP visit was done using a caliper of 0.25 times the standard deviation (SD); matching was done without replacement. Distributions of patient covariates before and after propensity score matching were compared using a χ2 test. Before and after propensity score matching, the percentages of visits with a related diagnostic test or a medication order on an NP/PA versus PCP visit were compared using a χ2 test.

Several sensitivity analyses were conducted. Results might be sensitive to the granularity of matching of NP/PA to PCP visits. Sensitivity of propensity score matching was tested with a finer caliper of 0.025 times the SD. Second, we examined percentages of visits with diagnostic radiology or medication orders by subgroups of visits classified according to the primacy of codes for presenting conditions, assuming that NPs/PAs or PCPs might use the EHR differently and, therefore, code visits differently according to sequence of “presenting” and “diagnosed” conditions. Finally, we estimated a logistic regression of each service order type as a function of NP/PA versus PCP using PROC GENMOD (SAS Institute, Cary, North Carolina) to evaluate whether clustering of service orders by provider might account for statistical significance of likelihood of a service type order by NP/PA or PCP.

All data management and statistical analyses were conducted using SAS version 9.4 (SAS Institute, Cary, North Carolina).


NPs/PAs attended to 16.2% of the visits (6724 of 41,404) with N/B pain as a primary or secondary diagnosis. NPs/PAs attended to 22% of the visits (24,190 of 109,844) with ARI as a primary or secondary diagnosis.

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