In this national study, U.S. primary care physicians referred patients for subspecialty care earlier when they based their referral decisions on patients' eGFR compared to when they based their referral decisions on serum creatinine. Over a third of primary care physicians significantly improved the timing of their decisions with the use of eGFR. Improved timing of referrals was greater among primary care physicians practicing in academic settings and presented with White hypothetical patients. These findings provide insight regarding the potential impact of clinical laboratories' automatic reporting of eGFR on clinical care and patient outcomes.
To our knowledge, this is the first U.S. study to demonstrate the effect of primary care physicians' use of eGFR on the timing of their subspecialty referral decisions. Prior non-US observational studies investigating the association of eGFR reporting with CKD specialty referral practices were limited by their inability to account for various clinical and non-clinical policy and resource trends which could have also impacted referral practices[28
]. Our study was designed to directly assess the impact of the use of eGFR on physician decision making under the same patient, provider, and system level influences. Our findings provide evidence that encouraging use of eGFR by primary care providers to assess kidney function and more widespread automatic reporting of eGFR by clinical laboratories could significantly improve the quality of care and clinical outcomes for patients with CKD by directly affecting physicians' clinical decisions. Earlier referrals to subspecialty care for the roughly one million U.S. adults with advancing CKD (defined as National Kidney Foundation Kidney Disease Outcome Quality Initiative stages 3 and 4 CKD with gross proteinuria) could impact several aspects of clinical care for these patients, including allowing for appropriate dosing of medications to accommodate impaired renal function, earlier avoidance of nephrotoxins which could hasten CKD progression, achievement of CKD directed blood pressure and lipid targets, treatment of early metabolic complications of CKD, as well as earlier preparation for renal replacement therapy, all of which have been recommended and many of which have been demonstrated to improve clinical outcomes[1
There was substantial variation in the levels of eGFR at which U.S. primary care physicians recommended referral (ranging from eGFR of 15 to 100 mL/min/1.73m2
), suggesting refinement of clinical practice guidelines to clarify the indications for referral may be needed. While very early referrals may be appropriate for patients with gross proteinuria or rapidly declining kidney function, very early referrals among some patients with less risk of progression (e.g. elderly persons with reduced but relatively stable kidney function) may be inappropriate with regard to resource utilization and availability of nephrologists[44
]. Guidelines' clarification of clinical circumstances requiring more urgent referrals, as well as dissemination of these recommendations, may provide primary care physicians with greater confidence to care for the growing number of patients with CKD.
Differences in serum creatinine based on patient race and gender are well-established (with greater serum creatinine levels among men and African Americans)[46
]. The extent to which our finding of physicians' greater improvement in the timing of referrals among Whites compared to African Americans reflects race-based inequities in care is unclear. Since we presented each physician with only one hypothetical patient scenario (featuring a patient of either White or African American race), we were unable to ascertain whether individual physicians' practice patterns would have changed if they saw patients of different races. It is highly possible later referrals of Whites based on serum creatinine reflects primary care physicians' lack of knowledge regarding the severity of kidney dysfunction associated with lower serum creatinine levels among Whites. In light of previous research demonstrating Blacks are more likely to receive later subspecialty referrals compared to Whites[4
], our findings of equal referral timing among African Americans and Whites when primary care physicians used eGFR to estimate kidney dysfunction provides some reassurance that the use of eGFR may help narrow race-based differences in the timing of subspecialty referrals. The extent to which physicians' enhanced use of eGFR could narrow racial disparities in the long-term clinical outcomes of patients with CKD merits further study.
There are limitations of this study. First, physicians' recommendations for referral based on a hypothetical case scenario may not reflect their real practice patterns. Further, serum creatinines provided in the scenario might have caused an anchoring effect for the respondents when providing recommendations for referral based on serum creatinine. However, the use of a hypothetical case allowed us to assess physicians' decision-making regarding referral under similarly realistic conditions, and the inclusion of serum creatinine in the scenario would not have impacted within-individual-physician differences in their referrals when using serum creatinine versus eGFR. Second, we did not assess the rationale for the timing of physicians' referrals, which may have been based on factors other than the eGFR (i.e. presence of proteinuria or diabetes). Third, the study sample size was small, and primary care physicians' response rate was limited, possibly limiting our ability to detect all significant associations and the generalizability of our findings. Nonetheless, participating physicians practiced in several regions of the U.S. and in a variety of practice settings enhancing our ability to identify physician characteristics associated with improvement in the timing of referrals. Finally, the cross-sectional design of our study limits our ability to assess the potential long-term effects of physicians' eGFR referral decisions on patients' clinical outcomes. However, extensive research documenting poor clinical outcomes for patients experiencing late referrals for subspecialty care supports the potential significance of our findings[3