Glycated hemoglobin is formed when hemoglobin is exposed to glucose in the blood, that is, whenever the body processes sugar, which renders the HbA1c suitable for testing diabetes.
Despite some limitations, HbA1c tests are very reliable.
How HbA1c is measured
Glycated hemoglobin is measured to identify the average plasma glucose, or your average blood sugar levels, over longer periods of up to 12 weeks.
Therefore, the results of an HbA1c test can show whether a person suffers from diabetes (both type 1 and type 2), although it is particularly useful at detecting diabetes mellitus (type 2), when coupled with a fasting blood glucose test.
Type 1 diabetes is better confirmed with random plasma glucose tests, with the HbA1c acting as diagnosis support.
Blood glucose test; image source: healthtap.com
Test results show no diabetes when scores are below 6.0% (the normal HbA1c), prediabetes when they are between 6.0% and 6.4%, whereas (type 2) diabetics will have an HbA1c of 6.5% and above.
People within the 6.0–6.4% range should discuss with their doctor about the changes they can bring into their lives to reduce the risk of developing diabetes further on.
The HbA1c can be measured with a simple blood test either taken from a finger or from the arm (more often). For children, a single drop of blood is enough, while in the case of pregnant women susceptible of gestational diabetes, the HbA1c test is replaced with an oral glucose tolerance test; that is because pregnancy can render HbA1c readings inaccurate.
HbA1c versus plasma glucose tests
HbA1c is different from blood glucose, in that an HbA1c reading shows how high your average blood sugar levels have been over the past 2 or 3 months, whereas a glucose test only shows what your current glucose levels are at the moment of the test. Moreover, while HbA1c values are measured in mmol/mol, blood glucose levels are measured in mmol/l.
Keeping diabetes under control with HbA1c
The HbA1c test shows whether or not you have diabetes or prediabetes, and in case you do have it, how well you are able to control it. This is important because the higher the HbA1c (i.e., the amount of sugar in your blood), the greater the risk of diabetes complications.
Note that this is not a one-off test, but the frequency of the HbA1c reading depends on various factors. More specifically, people with type 2 diabetes should have it done at least once per year; others can do it more often, for example, when they take new medication.
Generally, people with diabetes should strive to get their HbA1c to 6.5%, or 48 mmol/mol, but this varies with each individual; the HbA1c target depends on a person’s lifestyle, and also on the likelihood of developing hypos, both regular and severe.
However, HbA1c can be lowered to improve patients’ health. In fact, studies have shown that people with diabetes have a 50% greater chance of living within 5 years of discovery merely by cutting their HbA1c levels by less than 1%.
Broken down, a 1% improvement (or 11 mmol/mol) means a 25% reduction in the risk of micro vascular complications like diabetic kidney disease, retinopathy (eye disease), and neuropathy (a nerve disorder).
Moreover, if people with type 2 diabetes lower their HbA1c by 1%, it can diminish their risk of heart failure by 16%, of cataracts by 19%, and of peripheral vascular disease-caused amputation or death by as much as 43%.
Limitations of HbA1c testing
Apart from pregnancy, other circumstances that can affect the HbA1c test include illnesses (these can cause blood glucose levels to rise temporarily), anaemia (replaced with a fructosamine test because of insufficient hemoglobin to carry out an HbA1c reading), as well as hemoglobin variants.