November 12, 2024
Continuous Glucose Monitoring (CGM)
CGM provides detailed information about glucose variability and time spent in target ranges, which A1C alone does not capture. The preferred number of days of CGM has been determined as a minimum of 14 days of data with 70% sensor wear to generate an accurate report.
Key Terms:
GMI (Glucose Management Indicator) – An estimate of blood glucose control as reflected by what A1c level might be expected based on the patient’s average glucose.
TIR (Time In Range) - How often patients are able to stay within the goalposts of their ideal range (70-180mg/dL).
TIHypo (Time In Hypoglycemia) – How often patients are below 70mg/dL (Ideal < 4% of the time).
TIHyper (Time In Hyperglycemia) – How often patients are above 180mg/dL (Ideal < 25% of the time).
Glucose Variability (GV) – How much glucose varies from the mean or median glucose.
Time In Range greater than 70% has been shown in multiple analyses to correlate loosely with a hemoglobin A1C of about 7.0%. It also provides glucose data over a much shorter timeframe than hemoglobin A1C. This frees clinicians from the traditional hemoglobin A1C based 3-month cycle for visits, allows for more frequent changes to the diabetes regimen, and potentially reduces clinical inertia.
Using both A1C and GMI gives the information needed to maintain better control over blood sugar levels. While GMI can be helpful, it should complement, not replace, regular A1C testing and clinical judgment.
For purposes of gap closure, A1C should be completed at least twice yearly. GMI data is not currently able to upload to payers but has benefit in monitoring disease.