Endocrine Abstracts

Objective: To compare FreeStyle Libre Glucose management indicator (GMI) with HbA1c and fructosamine and assess factors related to the difference.

Methods: Persons with type 1 diabetes on FreeStyle Libre from a single diabetes centre whose sensor was active >70% of the time were included. Baseline characteristics, latest HbA1c, fructosamine, full blood count, total protein and albumin were collected from medical records. Ambulatory glucose profile data for 28-, 60- and 90-days period ending at the date of last available HbA1c and 14- and 21-days period ending at the date of last available fructosamine were collected from LibreView.

Results: A total 412 (54.1% females, age 43±15 years) type 1 diabetics were included. Median (IQR) HbA1c, GMI and fructosamine were 63 (54-73) mmol/mol, 58 (52-65) mmol/mol and 376 (338-419) mmol/l respectively. HbA1c correlated (P < 0.001) with 28-day (ρ = 0.827), 60-day (ρ = 0.838) and 90-day (ρ = 0.828) GMI. HbA1c correlated with 60-day GMI (P < 0.001) in Caucasian (ρ = 0.825, n = 248), Asian (ρ = 0.924, n = 25) and Black (ρ = 0.846, n = 13) ethnic groups. HbA1c was 3 (IQR -1 to 7) mmol/mol higher than 60-day GMI (P < 0.001, n = 304). The difference between GMI and HbA1c was ≤10% in 66% and ≤20% in 94% of patients. The difference did not differ across ethnicities (P = 0.379) but correlated (P < 0.01) positively with HbA1c and age, and negatively with time in target. Fructosamine (n = 103) correlated (P < 0.001) with 14-day (ρ = 0.449) and 21-day (ρ = 0.500) GMI and the correlation did not differ when fructosamine was corrected for albumin (ρ = 0.431 and ρ = 0.462 respectively; P < 0.001) or total protein (ρ = 0.469 and ρ = 0.500 respectively; P < 0.001).

Conclusions: Despite being lower than HbA1c, the 60-day GMI was within ±10% of HbA1c in 66% of patients. The correlation of HbA1c with corresponding GMI was stronger compared to that of fructosamine. GMI may be a good tool to identify patients with a glycation gap.