What Does HbA1c Measure? Prediabetes Levels and When It Fails
Glycated hemoglobin (HbA1c) sums up what your blood sugar has been like over the past two to three months. Here we explain what it measures, which figures mark prediabetes and diabetes, and in which situations the result is not reliable.
What glycated hemoglobin measures
Inside red blood cells, glucose binds to hemoglobin without the help of any enzyme. Once attached, it doesn't come off. It's the same chemistry that browns the crust of bread: the Maillard reaction.
A red blood cell lives for about 120 days. That is why this test reflects two to three months of glucose. The most recent month accounts for roughly half of the result.
The difference from fasting glucose is clear. Fasting glucose is a snapshot of one specific moment. HbA1c is the whole film. That long memory is its main advantage, but it can also be its weak spot.
Reference ranges: normal, prediabetes and diabetes
According to the American Diabetes Association, a result below 5.7% is normal. Between 5.7% and 6.4% is considered prediabetes. From 6.5% upward, it is classed as diabetes.
The WHO has accepted the 6.5% threshold since 2011. If there are no symptoms, the diagnosis is confirmed with a second test.
Some lab reports show two-digit figures. In that case the unit is millimoles per mole: 39 is equivalent to 5.7% and 48 is equivalent to 6.5%.
Why the prediabetes cutoff isn't the same everywhere
The 5.7% threshold is not universal. An international expert committee, in 2009, and the British health service set it at 6%. With a result of 5.8%, you would be told you have prediabetes in the United States, but not in the United Kingdom.
In Spain, both criteria are used, depending on which guideline each doctor follows. There is no switch that flips at an exact number. Risk rises gradually, and the cutoff is a matter of consensus.
Risk factors and how to reduce your risk
Risk increases with abdominal fat, a sedentary lifestyle, too little sleep and drinking sugary beverages every day.
In 2002, the Diabetes Prevention Program trial measured how much it can be slowed. Losing 7% of body weight and getting 150 minutes of activity a week, such as brisk walking, reduced new cases of diabetes by 58%. Metformin, the drug it was compared with, reduced them by 31%.
For a person weighing 80 kilos, that 7% is about five and a half kilos. The 150 minutes amount to half an hour, five days a week.
When the result can be misleading
The test assumes that red blood cells live for about 120 days. If they live for less time, the figure is distorted. After bleeding or during pregnancy there are many young red blood cells, with little sugar built up, and the result can come out misleadingly low. A recent transfusion also skews it.
Iron-deficiency anemia has the opposite effect: there are more old red blood cells, and the figure can come out higher. In addition, some genetic variants of hemoglobin confuse certain laboratory analyzers. In these cases, the doctor turns to other tests.
Symptoms that warrant an appointment
Don't wait for your next blood test if you are constantly thirsty, urinate a lot, lose weight without trying, have blurred vision or find that wounds are slow to heal. If so, make an appointment with your doctor.
Frequently asked questions
Do you need to fast before an HbA1c test?
This value reflects roughly ninety days, so a large meal the night before barely changes it.
If my fasting glucose is normal, can I rule out prediabetes?
No. Some people have normal fasting glucose but an HbA1c in the prediabetes range, often because their blood sugar spikes after meals.
What does a result of 48 mmol/mol mean?
It is equivalent to 6.5%, the threshold from which diabetes is diagnosed. A value of 39 mmol/mol is equivalent to 5.7%.
What situations can skew HbA1c results?
Bleeding, pregnancy or a recent transfusion can lower it; iron-deficiency anemia can raise it. Some genetic variants of hemoglobin also affect certain measuring devices.
Informative article written with the help of AI tools from the verified script of the video. The video is in Spanish.