Referral to Nephrologists Mitigates the Progression of Kidney Dysfunction in Patients with Type 2 Diabetes: A Causal Inference Study

Background: Chronic kidney disease is a major complication of type 2 diabetes, necessitating effective management to mitigate kidney progression. This study evaluates the effect of referrals from endocrinologists to nephrologists on kidney function in diabetic patients through causal inference analysis. Methods: This study included patients with type 2 diabetes who initially visited the diabetes clinic between July 2004 and November 2023. Patients were either referred to a nephrology clinic or continued under the care of endocrinologists. The slope of eGFR per year was calculated based on the annual median difference in yearly eGFRs, and cases were censored when the values dropped below 10ml/min/1.73m2. 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 30,160 patients who visited the diabetes clinic, 3,885 patients (13%) were referred to nephrologists (referral group), while others continued under the care of endocrinologists alone (no referral group). The referral group, compared to the no referral group, had low baseline eGFR (73 [IQR, 59–87] vs 88 [76–98] ml/min/1.73m2) and high uACR (38 [12–199] vs 14 [8–39] mg/g). The averaged treatment effect of referral to nephrologists displayed an improvement in the eGFR slope, with an increase of 5.8 (95% CI, 4.8–6.8) ml/min/1.73m2/year. The referral group exhibited higher usage of antihypertensive agents and hypoglycemic agents other than metformin (e.g., DPP-4i and SGLT2i) than the no referral group. Kidney biopsies were more frequently performed in the referral group than in the no referral group (3.8% vs 0.05%), and 50% of patients who received biopsies were diagnosed with other diseases, with or without diabetic nephropathy. Conclusion: Referral to nephrologists reduces the progression of kidney dysfunction in patients with type 2 diabetes, supporting the need for appropriate referral to nephrologists in type 2 diabetic patients.The event study plot of the nephrology referral on average treatment effect.