Referral to nephrologists is associated with the slow progression of kidney dysfunction in patients with type 2 diabetes mellitus.

Background: Although treatment guidelines exist, referrals and discussions among clinicians about the disease can lead to more appropriate treatment for the patient. This study evaluated the effects of referrals from diabetes clinics to nephrologists on kidney function in type 2 diabetic patients through causal inference analysis.

Methods: This study included patients with type 2 diabetes who initially visited the diabetes clinic between 2004 and 2023. Patients were either referred to nephrologists (named the referral group) or continued under the care of diabetologists in the diabetes clinic (named the non-referral group). The slope of the estimated glomerular filtration rate (eGFR) per year was calculated based on the annual median difference in yearly eGFRs, and cases were censored when the values dropped below 10 mL/min/1.73 m2. We applied a difference-in-differences model to this time-series dataset with an inverse propensity weighting estimator to evaluate the effect of referral to nephrologists.

Results: Among the 30,160 patients who initially visited the diabetes clinic, 3,885 (12.9%) were referred to nephrologists during follow-up. At the time of referral, the median (interquartile range) values of the eGFR and random urine albumin-to-creatinine ratio were 55.0 mL/min/1.73 m2 (40.3-76.8 mL/min/1.73 m2) and 107 mg/g (20-846 mg/g), respectively. The average treatment effect of referral to nephrologists was an improvement in the eGFR slope, with an increase of 5.8 mL/min/1.73 m2 (95% confidence interval, 4.8-6.8 mL/min/1.73 m2) per year. The effect of referral was greater in patients with a high risk of progression than in those with a low risk.

Conclusion: Referral to nephrologists is associated with slow progression of kidney dysfunction in patients with type 2 diabetes, supporting the need to evaluate how to facilitate timely referral for each patient as a next step.