Assessment of equations estimating average glucose among patients with diabetic kidney disease before dialysis

Objective

Estimation of average glucose (AG) from hemoglobin A1c (HbA1c) helps guide diabetes management, and thus several AG-HbA1c equations have been constructed. However, it is not clear whether estimated AG calculated from existing AG-HbA1c equations could evaluate glycemic control in patients diabetic kidney disease (DKD) before dialysis. This study is aimed at evaluating the accuracy of estimated AG which is calculated from existing equations to assess glycemic control in DKD before dialysis. Additionally, we examined the relationship between AG and HbA1c in DKD before dialysis.

Methods

In this retrospective study, we collected data of 71 Chinese patients with DKD before dialysis who had a complete flash glucose monitoring (FGM) data during hospitalization in a single center between August 2018 and August 2021 by casually sampling. Measured AG was derived from the FGM system and compared to estimated AG derived from a frequently used AG-HbA1c equation (that developed in ADAG study), in addition to a formula established in CKD (that of ADAG-CKD equation). Performance of AG-HbA1c equations was evaluated by mean absolute difference (MAD)/mean absolute relative difference (MARD) and Bland–Altman test. Linear regression analysis was used to investigate the relationship of AG and HbA1c in DKD before dialysis.

Results

Among the 71 DKD before dialysis, 80% were type 2 diabetes. The mean age was 57 ± 13.8 years, and mean eGFR was 66.3 ± 32.3 mL.min/(1.73 m²). Mean HbA1c was 8.4 ± 2.2 (%), and measured AG was 150.2 ± 40.3 (mg/dL). Measured AG was significantly overestimated by equations ADAG and ADAG-CKD. Both ADAG and ADAG-CKD equations did not reflect the measured AG accurately (MAD 2.42 vs. 3.42 mmol/L; MARD 33.3% vs. 46.7%, respectively; p < 0.01). We examined the relationship between AG and HbA1c in DKD before dialysis as follows: AG (mmol/L) = 0.48 × HbA1c (%) + 4.36. In addition, using multiple regression analysis, HbA1c, diabetes type, body mass index (BMI), and CKD stage explained 42% of the variability in measured AG (r = 0.68, R² = 0.42, p < 0.01).

Conclusions

HbA1c-derived estimated AG from existing equations may not accurately reflect measured AG in patients with DKD before dialysis. Diabetes type, BMI, and CKD stage should be considered when translating HbA1c into AG value in DKD before dialysis. It is advisable to adjust the AG-HbA1c equations for target population.