Estimating Glomerular Filtration Rate by Serum Creatinine, Cystatin C, and β2-Microglobulin in Older Adults: Results from the Canadian Study of Longevity in Type 1 Diabetes

Introduction Glomerular filtration rate (GFR) is routinely used for clinical assessment of kidney function. However, the accuracy of estimating equations in older adults is uncertain. Methods In 66 adults with ≥50 years type 1 diabetes (T1D) duration and 73 nondiabetic controls from age/sex-matched subgroups (65 ± 8 years old and 77[55%] were women) we evaluated the performance of estimated GFR (eGFR) by creatinine (Modification of Diet and Renal Disease [MDRD], Chronic Kidney Disease–Epidemiology [CKD-EPI] cr ), cystatin C (CKD-EPI cys , CKD-EPI cr-cys ), and β 2 -microglobulin (β2M) compared with measured GFR by inulin clearance (mGFR). Performance was evaluated using metrics of bias (mean difference), precision (SD), and accuracy (proportion of eGFR that differed by u003e20% of mGFR). Results Mean mGFR was 104 ± 18 ml/min per 1.73 m 2 (range: 70–154 ml/min per 1.73 m 2 ) and was not different between T1D and controls (103 ± 17 vs. 105 ± 19 ml/min per 1.73 m 2 , P = 0.39). All equations significantly underestimated mGFR (bias: −15 to −30 ml/min per 1.73 m 2 , P 2 ( P = 0.61). Bias was greatest in cystatin C–based equations. Precision was lowest for β2M (SD: 43.5 ml/min per 1.73 m 2 , P cysC (69.1%, P 2 ). Results were similar between T1D and controls except that β2M had lower performance in T1D. Conclusion Better estimates of GFR in older adults are needed for research and clinical practice, as this subgroup of the population has an amplified risk for the development of chronic kidney disease (CKD) that requires accurate GFR estimation methods.