Early Worsening of Diabetic Nephropathy in Type 2 Diabetes After Rapid Improvement in Chronic Severe Hyperglycemia. Diabetes Care 2021;44:e55–e56

We thank Dr. Larroumet and her colleagues for their interest in our article (1), in which we described severe, permanent loss of renal function in four people with type 2 diabetes after rapid correction of chronic severe hyperglycemia. In a larger group of people with type 2 diabetes whose glycemic control had improved substantially, Larroumet et al. (2) found no evidence that renal function was adversely affected. However, important differences between their cohort and ours can probably explain the different outcomes. First, the rate, magnitude of reduction, and nadir value in A1C differed. In their cohort, the reduction in A1C took place “during the year preceding admission” and was required to be only >27 mmol/mol for the patient to be classified as a “rapid decliner,” and the mean nadir value reached was 77 mmol/mol. In our cohort, the reduction in A1C occurred within 6 months, at which time the mean reduction in A1C was 73 mmol/ mol and the mean A1C was 48 mmol/ mol. Thus, in our cohort the fall in A1C was more rapid and more profound, and the nadir A1C was lower. A further difference was that the baseline renal function in their cohort (mean estimated glomerular filtration rate [eGFR] 85 mL/min/1.73 m, at an average age of 63 years) was substantially better than in the subjects we describe (mean eGFR 71 mL/min/1.73 m, at an average age of 53 years). We agree that the phenomenon we observed was exceptional and suspect it was linked both to relatively impaired renal function at baseline as well as the rapid and profound reduction in A1C.