From the Guidelines
Dexcom GMI% (Glucose Management Indicator) does correlate with HbA1c (Hemoglobin A1c), as evidenced by the strong correlation (r = 0.92) found in the ADAG study 1. The correlation between Dexcom GMI% and HbA1c is based on the principle that both measurements reflect average glucose levels, albeit through different methods.
- HbA1c measures the glycation of hemoglobin in red blood cells over a period of 2-3 months.
- GMI, on the other hand, calculates an estimate based on direct glucose readings from continuous glucose monitoring (CGM) data over a shorter timeframe, typically 14 days. Key points to consider include:
- The American Diabetes Association (ADA) and the American Association for Clinical Chemistry have determined that the correlation is strong enough to justify reporting both the HbA1c result and the estimated average glucose (eAG) result when a clinician orders the HbA1c test 1.
- The mean plasma glucose numbers are based on a large number of readings, 2,700 per HbA1c measurement, in the ADAG trial, which assessed the correlation between HbA1c and frequent blood glucose monitoring and CGM in 507 adults 1. Individual variations may exist, and some patients may have a larger difference between their GMI and actual HbA1c due to factors like red blood cell lifespan, hemoglobin variants, or other physiological differences. However, for practical purposes, patients using Dexcom CGM can use their GMI as a reasonable approximation of their HbA1c between laboratory tests, though the laboratory HbA1c remains the gold standard for long-term glucose control assessment in clinical settings.
From the Research
Correlation Between Dexcom GMI and HbA1c
- The correlation between Dexcom GMI and HbA1c has been studied in several research papers 2, 3, 4, 5.
- A study published in 2024 found a moderate correlation between GMI and HbA1c (r = 0.68) in patients with type 2 diabetes treated by hemodialysis 2.
- Another study published in 2023 also found a moderate correlation between GMI and HbA1c (r = 0.68-0.71) in adults with type 2 diabetes 3.
- However, the same study found substantial variability in GMI at any given value of HbA1c, with a root mean squared error of 0.66-0.69 percentage points 3.
- A real-world analysis published in 2021 found significant discordance between laboratory-measured HbA1c and CGM-estimated HbA1c (eA1C), with 50% of patients having a difference of ≥0.5% and 22% having a difference of ≥1% 4.
- A retrospective observational cohort study published in 2024 found that the measured HbA1c was 0.34% higher than the CGM-derived GMI in patients with type 1 and type 2 diabetes mellitus 5.
Factors Affecting the Correlation
- Advanced chronic kidney disease has been found to increase the discordance between HbA1c and GMI 4.
- Anemia, polycythemia, cirrhosis of the liver, and metabolic dysfunction associated with steatohepatitis (MASH) can also affect the measured HbA1c and should be excluded when comparing HbA1c and GMI 5.
- The use of different CGM devices, such as Dexcom G6 and Freestyle Libre 3, may also affect the correlation between GMI and HbA1c 5.