Glycosylated hemoglobin (HbA)1c) has long served as a key indicator for diabetes management. However, with the increasing availability and adoption of continuous glucose monitors (CGMs), clinicians now have access to a large number of additional data points. A thorough understanding of CGM metrics is required to assist clinicians in making medical management decisions.
Key metrics derived from CGM, such as time in range (TIR) and glucose management index (GMI), provide important data for assessing glucose metabolism. Different from HbA1cprovides an estimated average blood sugar level. TIR highlights the time you are in the normal blood sugar range. Similarly, GMI estimates her approximate HbA.1c In a shorter period of time than traditional HbA1c Under test. However, it is important to note that GMI and HbA:1c Although they can be used together, these are separate measures that must be interpreted carefully.
1. Why is CGM data important in primary care?
Most outpatient visits for patients with type 2 diabetes occur in primary care.1 Pilla et al. analyzed data from two surveys: the National Ambulatory Care Survey and the National Hospital Ambulatory Care Survey. Data for these surveys included information from office-based physician visits and hospital-based (emergency and outpatient) visits. The authors found that from 2009 to 2015, the annual average number of visits for people with diabetes was 61.4 million, with the majority coming to primary care clinics (32 million), followed by specialty clinics (11.1 million), and hospitals. We found that it was occurring in outpatient and emergency clinic settings. Department (12.1 million).1
The American Diabetes Association describes CGM as an important technology.2 However, adaptation in clinical practice has been slow. Battelino et al reported that the success rate of his CGM use in clinical practice was low and, as a result, he also had a low rate of use of CGM data.3 Additionally, disparities exist in CGM usage. Although CGMs are covered by most private insurance plans and Medicare, access to these devices is not always equitable. The American Diabetes Association noted that while people of color on Medicaid are less likely to use CGMs, young people are prescribed CGMs more frequently and Black Americans have the least access to CGMs. .2
Bergenstal et al write that a smooth transition from estimated HbA:1c GMI Interpretation includes instructions on how to interpret and use the GMI effectively in clinical practice.Four Dr. Martens discussed that improving the control of blood glucose levels in patients with diabetes managed in primary care requires the expertise of primary care clinicians in interpreting CGM data.Five Clinical inertia is a barrier to CGM use.6
2. What is time in range?
Time of arrival (TIR) is another useful metric that is different from both HbA.1c and GMI. TIR typically refers to the percentage of days a patient’s blood sugar levels are between 70 and 180 mg/dL (euglycemic). Measuring is important because complications can occur if glucose values are consistently outside of these parameters. TIR goals vary according to different patient profiles (Table 1).3,8 Diabetic complications are correlated with less time spent within the euglycemic target range. According to a study by Goldenberg et al., there is an inverse relationship between TIR and HbA.1c (The higher the TIR, the lower the HbA)1c) Results in a sample of patients with type 2 diabetes using basal insulin.7
3. Complications associated with decreased TIR
Beck et al. sought to validate TIR as an outcome measure for diabetes. The authors used data from the Diabetes Control and Complications Trial (DCCT) to investigate the association of TIR with diabetic complications such as retinopathy and microalbuminuria.9 Specifically, data were collected from fingerstick samples from 1440 patients at seven different times of the day (i.e., before and after meals and at bedtime). The progression of retinopathy was evaluated after 6 months and microalbuminuria was evaluated annually. In this study, the average TIF for the 7-point profile was found to be 41 ± 16%. The risk of developing retinopathy or microalbuminuria increased significantly with lower TIR. For every 10 percentage points, the adjusted hazard rate for developing retinopathy increased by 64% (95% CI, 51% to 78%) and developing microalbuminuria increased by 40% (95% CI, 25% to 56%). ) increased. Decrease in TIR (P <0.001 each). The authors concluded that low TIR is strongly associated with the risk of microvascular complications such as microalbuminuria and retinopathy and should be accepted as an endpoint in clinical trials.9
“
In addition to time in range, clinicians must also consider time above target (hyperglycemia) and time below target (hypoglycemia) when deciding on treatment.
In addition to retinopathy and microalbuminuria, TIR is associated with both microvascular and macrovascular complications in diabetes, including peripheral neuropathy, markers of cardiovascular disease, cardiovascular autonomic neuropathy, and albuminuria. Associated with common further complications.Ten The score is a logical indicator of glucose estimates related to complications of type 2 diabetes. However, Saboo et al. questioned whether TIR should be the only aggregate measure of type 2 diabetes for management. The authors also highlight the role of training programs in using TIR as a complementary clinical indicator to HbA.1c In decision making.Ten
The study by Lu et al. included samples from 6225 adult patients with type 2 diabetes from January 2005 to December 2015.11Time in range was estimated from CGM data. Participants were divided into four groups according to TIR>85%, TIR 71%~85%, TIR 51%~70%, and TIR≤50%. Cox proportional hazards regression models were used to assess the association between different TIR ranges and the risk of all-cause and cardiovascular mortality. The authors found an inverse association between TIR and risk of all-cause and cardiovascular mortality in patients with type 2 diabetes (Table 2). The authors concluded that TIR is supported as a valid marker of long-term outcome.11
Four. What is a blood sugar control index?
GMI is calculated almost exclusively from CGM data and uses the same scale as HbA.1c However, this is based on short-term average glucose values rather than long-term glucose exposure.11 Gomez-Peralta et al discussed that three main indicators are used to assess diabetes: mean blood glucose level, estimated HbA.1c (eHbA1c), GMI.12 eHbA1c is the average amount of glycosylation in red blood cells and is influenced by parameters such as glycosylation rate, average red blood cell production rate and half-life, hemoglobinopathies, age, and drugs.12 Measurement of HbA1c This can be affected by the timing of sample extraction and the machinery used.13 HbA1c GMI reflects two to three months’ worth of data, whereas GMI can reflect estimated blood sugar levels in just two weeks.2
Although GMI and eHbA1c are based on average glucose, the two are calculated differently. The calculation for GMI is GMI (%) = 3.31 + 0.02392 x. [mean glucose in mg/dL]. The calculation for eHbA1c is: eHbA1c (%) = 3.38 x. [mean glucose in mg/dL].13 Gomez-Peralta et al emphasized that eHbA1c does not have a 1:1 match with HbA.1cGMI is considered equivalent to eHbA1c.12
5. Is GMI the same as HbA?1c?
GMI is expected to be different from HbA1c. Both measurements can be interpreted relative to each other.For example, if HbA1c If it is higher than the GMI, this may mean that the individual is a hyperglycinator.12 For HbA1c If it is lower than the GMI, this may mean the person is a low glycator. Therefore, if diabetes management decisions are made based solely on her HbA,1cwhich may increase the patient’s risk of developing hypoglycemia.13 Clinicians should not aim for HbA that is too low.1cto prevent spending excessive time in a hypoglycemic state.13 Bergensthal added that this difference could be due to red blood cells having a longer life span than normal, or due to biological or genetic variations.3
Another important difference is that HbA1c GMI reflects the level of glycosylation of red blood cells, whereas GMI is based on glucose data from CGM taken from interstitial fluid.
6. How to compare GMI and HbA1c?
As mentioned above, GMI is a useful metric to approximate HbA.1cespecially if you need a 10-14 day summary.14 However, it is different from HbA.1c And it’s not exactly the same as eHbA1c. This metric measures average blood sugar levels from continuous blood glucose meter data and provides an estimate of average blood sugar levels with results available in 2 weeks, compared to 2-3 months for HbA. To do.1c.
Fang et al. conducted a prospective cohort study of 144 adults with type 2 diabetes and sleep apnea who were not taking insulin.15 Participants wore two sensors (Dexcom G4 and Abbott Libre Pro).The authors found that HbA1c and GMI had only a moderate positive correlation ( r =0.68 to 0.71), with 36% to 43% of participants having an absolute difference between HbA.1c and GMI of 0.5 percentage point or more, and 9–18% of participants had an absolute difference of more than 1 percentage point.15 Wybrańczyk et al. discussed other factors that may influence GMI, including ethnicity and racial genotype, adipose tissue, blood sugar fluctuations, age, pregnancy, and chronic kidney disease (which causes impaired waste removal). We are discussing.16
What does this mean for your practice?
When using available CGM data to determine diabetes treatment, decisions can be based on multiple goals.For example, if HbA1c is 6.9% and the TIR is 50%, the patient can increase the TIR to more than 70%. Additionally, clinicians may consider counseling patients that increasing TIR may reduce microvascular and macrovascular complications.The clinician and patient team should aim to discuss her HbA1cDepending on the , GMI, and TIR levels, regular follow-up visits will be conducted to achieve the goals.
TIR is a useful additional metric to consider when assessing proper control of blood sugar levels, with the goal of spending more time on TIR. However, it is important to note that TIR is not the gold standard and goals vary depending on the patient’s age and pregnancy status. For older patients, especially those using insulin, hypoglycemia is a greater threat.16 Therefore, patient profile and risk factors should be considered when setting goals.
In addition to TIR, clinicians should also consider time above target (hyperglycemia) and time below target (hypoglycemia) when deciding on treatment. Time spent above, during, and below the goal is an important focus. If both the clinician and patient are aware of problem times, the clinician and patient can emphasize lifestyle changes to increase her TIR.Overall, the combination of TIR and HbA1c Provides critical information to clinicians and patients. This broader perspective creates an opportunity to discuss improvement strategies regarding lifestyle changes. Clinicians skilled in interpreting CGM data will be better equipped to address the devastating complications of this ubiquitous disease.
