Estimating glomerular filtration rate: Performance of the CKD-EPI equation over time in patients with type 2 diabetes

Aims: To assess the performance of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation at baseline and longitudinally in people with type 2 diabetes.

Methods: Adults with type 2 diabetes attending Austin Health, Melbourne, with ≤ 3 prospective GFR measurements were included in this retrospective study. Plasma disappearance rate of DTPA (diethylene-triamine-penta-acetic acid) was used to calculate measured GFR (mGFR) and compared to estimated GFR (EGFR). The agreement between mGFR and EGFR was estimated using Intraclass Correlation Coefficient (ICC). 

Results: 152 patients had a median of 4 (IQR: 3, 5) mGFR measurements over a period of 11 years (IQR: 9, 12). The difference between mGFR and EGFR increased proportionally to the magnitude of the GFR, increasing by 0.2 ml/min/1.73 m² for every 1 ml/min/1.73 m² increase in mGFR, indicative of proportional bias. At lower mGFR levels, EGFR overestimated mGFR, and at higher mGFR levels, EGFR underestimated mGFR. There was a significant association between LDL cholesterol, triglycerides, HbA1c, diastolic blood pressure and the difference between mGFR and EGFR.

Conclusions: The CKD-EPI formula underestimates mGFR and the rate of decline of mGFR in patients with type 2 diabetes with an mGFR greater than 60 ml/min/1.73 m². The association between LDL cholesterol, triglycerides, HbA1c, diastolic blood pressure and the difference between mGFR and EGFR warrants further study.