What is glycated hemoglobin (HbA1c)?
Glycated hemoglobin, medically known as HbA1c or A1c, is a blood test that reflects the average glucose level over the past 2-3 months. It is considered the "gold standard" in assessing glycemic control and is essential for diabetes management.
But what exactly is it? Hemoglobin is a protein in red blood cells that carries oxygen throughout the body. When glucose circulates through the blood, some of it attaches to hemoglobin - a process called "glycation". The higher the blood glucose level, the more glucose attaches to hemoglobin.
Red blood cells live approximately 120 days (3 months). Therefore, measuring the percentage of glycated hemoglobin tells us what the average blood glucose was over this period. It's like a "report card" of your glycemic control from the last quarter.
Normal values of glycated hemoglobin
Interpreting HbA1c values is relatively straightforward:
Below 5.7% - normal. Glucose metabolism is functioning optimally.
5.7% - 6.4% - prediabetes. There is an increased risk of developing type 2 diabetes mellitus. Lifestyle modifications (diet, exercise) can prevent or delay progression.
6.5% or higher - diabetes. Diagnosis of diabetes mellitus if confirmed by two separate tests or by a test combined with clinical symptoms.
For people with already diagnosed diabetes, therapeutic targets recommended by international guidelines are:
Below 7% (53 mmol/mol) - general target recommended by the ADA (American Diabetes Association) for most adults with diabetes.
Below 6.5% (48 mmol/mol) - stricter target, recommended for young people, recently diagnosed, without complications and without significant risk of hypoglycemia.
Below 8% (64 mmol/mol) - more relaxed target, recommended for elderly people, with multiple comorbidities or with a history of severe hypoglycemia.
How HbA1c correlates with average blood glucose
A practical aspect that many patients appreciate is the correlation between HbA1c and estimated average glucose (eAG - estimated Average Glucose). This allows you to "translate" the HbA1c percentage into a blood glucose value that you understand from daily measurements:
HbA1c 6% corresponds to an average blood glucose of approximately 126 mg/dL. HbA1c 7% corresponds to 154 mg/dL. HbA1c 8% - 183 mg/dL. HbA1c 9% - 212 mg/dL. HbA1c 10% - 240 mg/dL.
Each percentage point of HbA1c represents a difference of approximately 29 mg/dL in average blood glucose. This correlation is useful, but should be viewed with caution - two patients with the same HbA1c may have very different glucose profiles.
Limitations of HbA1c - why it doesn't tell the whole story
Although glycated hemoglobin is a valuable indicator, it has important limitations that both patients and doctors need to know:
The paradox of the average
HbA1c is an average. And an average can hide dangerous extremes. A patient who oscillates between 40 mg/dL (severe hypoglycemia) and 300 mg/dL (marked hyperglycemia) may have the same HbA1c as a patient with stable blood glucose at 150 mg/dL. Both have the same "average", but their health status and risk of complications are dramatically different.
Conditions that falsify the result
Anemia, iron deficiency anemia, thalassemia, hemoglobinopathies, recent blood transfusions - all these conditions can significantly influence the HbA1c value, making it higher or lower than reality. In patients with these conditions, the doctor will use alternative tests (such as fructosamine or glycated albumin).
Does not reflect glucose variability
Glucose variability - large fluctuations in blood glucose throughout the day - is an independent risk factor for diabetes complications. HbA1c does not capture this variability. A patient with HbA1c of 7% and low variability is in a better situation than one with the same HbA1c but with extreme fluctuations.
How CGM helps improve HbA1c
This is where continuous glucose monitoring comes in. CGM sensors provide exactly the information that HbA1c cannot provide: detail, context, and variability.
Pattern visualization
With a CGM sensor, you see exactly what happens to your blood glucose after each meal, after exercise, during stress, at night. You identify patterns: "Ah, every time I eat pasta in the evening, I have a spike to 250 mg/dL for 3 hours." This awareness leads to concrete behavioral changes.
TIR - the indicator that complements HbA1c
CGM introduced a new, extremely useful indicator: TIR (Time in Range) - time spent in the optimal glucose range (70-180 mg/dL). International guidelines recommend a TIR of at least 70% for adults.
TIR correlates with HbA1c: a TIR of 70% corresponds approximately to an HbA1c of 7%. But TIR provides crucial additional information - it shows how much time you spend both above (hyperglycemia) and below (hypoglycemia) range.
GMI - estimated HbA1c from CGM data
CGM sensors automatically calculate GMI (Glucose Management Indicator) - an estimate of HbA1c based on the sensor's continuous data. The advantage is that GMI updates continuously (you don't have to wait 3 months for the next blood test) and can be calculated for any period (last week, month, 14 days).
How type 2 diabetes responds to CGM monitoring
A study published in JAMA demonstrated that people with type 2 diabetes who used CGM reduced HbA1c by 0.4% more than those who used only a glucometer, over a 6-month period. But beyond the numbers, patients reported a much better understanding of their own condition and increased motivation for lifestyle changes.
People with type 2 diabetes who see in real time how a 30-minute walk "flattens" the glucose spike after a meal become much more motivated to move. Those who see the difference between a small and a large portion of rice make better food choices not out of obligation, but out of conviction.
Practical strategies for reducing HbA1c with CGM help
1. Set reasonable alarms - don't set your hyperglycemia alarm at 140 mg/dL if your post-meal blood glucose frequently reaches 200. You'll be bombarded with alarms and ignore them. Start at 250 mg/dL and lower gradually as control improves.
2. Focus on a single objective - don't try to fix everything at once. This week, concentrate on post-breakfast blood glucose. Next week, on the nighttime one. A step-by-step approach is sustainable.
3. Use AGP reports - the Ambulatory Glucose Profile (AGP) report available in CGM apps shows a visual summary of blood glucose over 14 days. Bring it to each medical appointment - it's much more informative than a single HbA1c value.
4. Identify the "culprits" - foods that raise your blood glucose the most. With CGM, you identify them quickly and can choose alternatives. It's not about severe restrictions, but about informed choices.
5. Monitor the effect of exercise - see in real time how exercise lowers blood glucose. This positive feedback is extraordinarily motivating.
HbA1c and risk of complications - why every tenth matters
The DCCT/EDIC study (the largest and longest clinical study on type 1 diabetes) and the UKPDS study (the equivalent for type 2) clearly demonstrated: each 1% reduction in HbA1c brings significant benefits.
Reducing HbA1c by 1% is associated with: 37% reduction in the risk of microvascular complications (retinopathy, nephropathy, neuropathy), 21% reduction in diabetes-related deaths, 14% reduction in myocardial infarction and 43% reduction in amputations or deaths caused by peripheral vascular disease.
These figures are impressive and highlight why investing in a CGM sensor for continuous glucose monitoring may be one of the best decisions you make for your long-term health.
Common mistakes in interpreting HbA1c
In my practice, I observe several recurring mistakes related to the interpretation of glycated hemoglobin:
Exclusive focus on the number - a patient with HbA1c of 7.2% who "misses" the target of 7% is not a failure. The difference of 0.2% is minimal, and context matters more than the exact number. If it came from 9%, the progress is remarkable.
Comparing with other patients - each person has a unique metabolic profile. An HbA1c of 7.5% in a 75-year-old patient with multiple comorbidities is an excellent result. The same level in a 25-year-old recently diagnosed is a good result. The same level in a 25-year-old recently diagnosed may need optimization.
Ignoring variability - as I mentioned, a "good" HbA1c can hide dangerous fluctuations. That's why combining the HbA1c test with data from a CGM sensor provides the complete picture you need for informed decisions.
When HbA1c should be tested and how the test is done
The HbA1c test is done through a simple venous blood draw (fasting is not required - you can eat beforehand). It is recommended:
Every 3 months - for people with diabetes who have not reached their therapeutic target or who have recently changed treatment.
Every 6 months - for people with stable diabetes who have reached and maintain their HbA1c target.
Annually - for people with prediabetes, as screening.
The result is usually available within 24-48 hours of collection.
Monitoring HbA1c with modern CGM sensors
The variety of CGM sensors available on the Romanian market has increased significantly, making this technology accessible to more and more patients. Each model offers automated reports that include HbA1c estimation (GMI), time in optimal range (TIR) and detailed graphs of the glucose profile.
These reports, automatically generated by the sensor app, are valuable tools that you can present to your doctor at each appointment. They complement the laboratory HbA1c test with information that a single blood test cannot provide: variability, patterns and individual response to different foods, activities and medications.
