Effects of Tirzepatide Versus Insulin Glargine on Cystatin C–Based Kidney Function: A SURPASS-4 Post Hoc Analysis

OBJECTIVE: Tirzepatide reduces HbA(1c) and body weight, and creatinine-based estimated glomerular filtration rate (eGFR) decline. Unlike creatine-derived eGFR (eGFR-creatinine), cystatin C–derived eGFR (eGFR-cystatin C) is unaffected by muscle mass changes. We assessed effects of tirzepatide on eGFR-creatinine and eGFR-cystatin C. RESEARCH DESIGN AND METHODS: Our primary outcome was eGFR change from baseline at 52 weeks with pooled tirzepatide (5, 10, and 15 mg) and titrated insulin glargine in adults with type 2 diabetes and high cardiovascular risk (SURPASS-4). RESULTS: Least squares mean (SE) eGFR-creatinine (mL/min/1.73 m(2)) changes from baseline with tirzepatide and insulin glargine were −2.5 (0.38) and −3.9 (0.38) (between-group difference, 1.4 [95% CI 0.3–2.4]) and −3.5 (0.37) and −5.3 (0.37) (between-group difference, 1.8 [95% CI 0.8–2.8]) for eGFR-cystatin C. Baseline, 1-year, and 1-year change from baseline values significantly correlated between eGFR-cystatin C and eGFR-creatinine. Measures of eGFR changes did not correlate with body weight changes. CONCLUSIONS: Tirzepatide slows the eGFR decline rate, supporting a kidney-protective effect.