eGFR overestimates kidney function in patients with poor glycemic control

Poor glycemic control causes overestimations in calculations of estimated glomerular filtration rate (eGFR), according to a recent study that developed a formula to correct the problem.

The study included 40 patients with diabetes and 40 patients without diabetes, all of whom had their GFR evaluated by inulin clearance. Their eGFRs were also calculated using serum creatinine and serum cystatin C and both measures together. Researchers found that patients with and without diabetes did not significantly differ in their inulin clearance, but they did have significant differences on all 3 of the eGFR results. The diabetic patients had significantly higher eGFRs than the nondiabetic patients. Results were published early online by Diabetes Care on Oct. 15.

After analyzing various factors, the researchers found that patients with higher hemoglobin A1c (HbA1c) and glycated albumin levels had greater inaccuracy in their eGFRs. They then developed equations to use these factors to correct the overestimations. Testing showed that their new equations (which used measurements of creatinine or cystatin C and HbA1c or glycated albumin) improved eGFR calculation for all patients, but especially those with diabetes. The formula to correct eGFR using HbA1c and creatinine (the measures most commonly available in clinical practice) is eGFR (based on creatinine) divided by (0.428 + 0.085 × HbA1c).

This new formula is a clinically useful and feasible way to more accurately calculate the eGFR of patients with diabetes and kidney disease, the study authors concluded. Overestimations of renal function using the current formulas could delay needed treatment for diabetic patients, especially those with poor glycemic control, they added. The authors noted that the study was limited by its small size and use of a single center, so the results should be confirmed in larger studies. Future research should also construct formulas like this one for different races, the authors recommended.