HbA1c is an indicator of long-term glucose levels. It has been recommended for diagnosing diabetes by the American Diabetes Association, along with other tests. Increased HbA1c can also reveal prediabetes, a health condition that’s not quite diabetes yet. Ideally, you want to keep your HbA1c low and stable. Read on to find out why you could check your values and whether they are in the normal range.
What is HbA1c?
Glycated hemoglobin (HbA1c) is an important indicator for long-term glucose levels and has been recommended for use in the diagnosis of diabetes mellitus (DM) by the American Diabetes Association (ADA) and World Health Organization (WHO) .
HbA1c is created when glucose binds to hemoglobin, which is found in red blood cells .
How High Blood Sugar Creates HbA1c
Red blood cells are exposed to glucose in the blood. The higher the blood glucose level gets the more HbA1c forms throughout the lifespan of a red blood cell .
The lifespan of a red blood cell varies from person to person but averages out to approximately 117 days in men and 106 days in women. Therefore, the HbA1c is an index of average blood sugar levels over the preceding 2 to 3 months. Of this 2 – 3 month period, the immediately preceding 30 days contribute 50% to HbA1c .
Normal adult hemoglobin consists predominantly of HbA1, of which HbA1c comprises approximately 5% .
However, HbA1c does not always correlate with blood glucose levels. It is possible to have high blood glucose but low HbA1c due to the presence of hemoglobin variants, inflammation, or other factors that increase red blood cell turn over.
If your Red Blood Cells live longer than 90 days or your RBCs are smaller (as measured by MCV in a blood test), then your HbA1C will be artificially higher.
A healthcare profession will take a blood sample from your arm, which will be sent to the lab to measure your HbA1c levels. Finger prick tests can use a single drop of blood to get a reading, which is often more convenient for children or people who have difficulty giving larger blood samples.
Your doctor will usually order this test as part of a routine health checkup or if you are at risk of diabetes. If you have diabetes, he or she will order the test to monitor your health status or the influence of medication changes. Some studies even suggest that doctors order and re-order this test more often than is needed in most cases .
You don’t need to prepare for the test in any particular way or fast, unless you are also testing your fasting blood glucose at the same time. Check with your health care provider to make sure you come prepared.
How Often Should Test HbA1c?
Diabetic patients with stable blood glucose levels should test HbA1c twice a year .
Quarterly monitoring might be indicated in patients with newly diagnosed or pregnancy-associated diabetes, rapidly changing HbA1c levels, treatment changes, insulin use, or history of hypoglycemia (low blood sugar) .
Testing HbA1c five or more times per year is redundant because HbA1c is a measure of average blood sugar over three months .
Advantages of HbA1C Over Other Blood Glucose Tests
- The HbA1c test can be taken at any time and does not require fasting .
- It is unaffected by physical activity or stress prior to testing .
- As a marker of longer-term blood sugar levels, it is unaffected by short-term hormonal surges .
- As a test, HbA1c has a low variability, both when measured in a single individual, and among people .
- HbA1c is more stable than glucose at 37°C .
- Symptomatic patients can be tested immediately at the same visit, saving costs .
HbA1c can be measured in percent or mmol/mol (mili-mols per mol).
Measuring HbA1c percentages are considered to be the “old way” and most labs nowadays report its values as mmol/mol.
If you need to convert between the two, the Austalian Diabetes Society recommends the following formula :
Old (%) = 0,0915 New (mmol/mol) + 2,15%
New (mmol/mol) = 10,93 Old (%) – 23,5 mmol/mol
As an example, using this formula, 5% HbA1c equals 31 mmol/mol (54.7-23.5).
HbA1c Normal Range
In Healthy People
In healthy people, HbA1c values range between 4.0% and 5.6% .
Screening for Prediabetes
People with HbA1c values of 5.7 – 6.4% (39 – 46 mmol/mol) be considered high risks for diabetes .
In 2015, the American Diabetic Association (ADA) suggested that an HbA1c of 5.7 – 6.4% (39 – 46 mmol/mol) was reasonable for the diagnosis of pre-diabetes and that patients with HbA1c > 6.0% (>42 mmol/mol) should be considered to be at very high risk for developing diabetes .
Values ≥ 6.5% may indicate diabetes .
However, HbA1c as a single measurement is not adequate to diagnose diabetes . In one study HbA1c resulted in a significantly lower diabetes detection (3.6%) compared with diabetes defined by a 2-hour post-meal blood glucose test (9.2%) .
What Causes Normal HbA1c Levels to Vary?
1) Seasonal changes
HbA1c levels were reported to be higher in colder (January-March) than in warmer (July-September) months .
This variation amounts to about 0.3% (3.3 mmol/mol). These differences may be due to differences in exercise, carbohydrate intake, and the number of illness events between summer and winter months .
2) Ethnic differences
HbA1c levels are often reported to be different depending on race, ethnicity, and ancestry.
African-Caribbean and South Asian subjects were reported to have HbA1c levels 0.27 – 0.4% higher compared to those with European ancestry, despite lower fasting blood glucose in oral glucose tolerance tests [8, 16].
In South Africa, Black African patients with diabetes were more likely to reach the HbA1c target (<7%) and less likely to have eye, kidney, or cardiovascular diabetic complications .
3) Genetic Variants of Hemoglobin
HbA1c results can be inaccurate in persons with elevated amounts of hemoglobin variants. These variants (Hemoglobin S, C, E, and F) are more prevalent in non-Caucasians .
Hemoglobin S is found in approximately one in 12 African Americans, one in 100 Hispanics and other races .
Hemoglobin C is found in approximately one in 50 African Americans .
Hemoglobin E is associated with Asian descents, particularly southeast coastal Asia, with up to 30% in some areas .
Hemoglobin F is the normal hemoglobin typically found in a fetus and in low concentration in adults. In some genetic diseases like Hereditary Persistence of Fetal Hemoglobin, Sickle Beta Thalassemia, and some other diseases, hemoglobin F can be elevated .
4) Gender Differences
Men have to undergo greater metabolic deterioration and put on more visceral fat to develop HbA1c-defined diabetes than do women .
Patients aged over 70 have a 0.47% higher HbA1c compared to those under 30 .
One study argues against the increase of HbA1c with age though .
6) Recent Blood Donation
HbA1c decreases after donating blood. Therefore, HbA1c levels are likely to be underestimated after blood donation in patients with diabetes mellitus .
This is as a result of lower hemoglobin after giving blood and doesn’t mean that your blood sugar levels are lower.
HbA1c levels fluctuate very slightly during pregnancy. HbA1c levels decrease during the second trimester of a normal non-diabetic pregnancy and rise during the third trimester .
An HbA1c of 5.9 – 6.7% (41 – 49 mmol/mol) identifies a higher-risk group of women with gestational diabetes .
HbA1c>5.9% (41 mmol/mol) is associated with increased risk of large infants, cesarean section and high blood pressure .
One study showed that women with HbA1c over 5.9% showed a 3-fold higher rate of large infants and high blood pressure (preeclampsia) .
Another study showed that not obtaining HbA1c within the normal range before delivery was associated with a 6 fold increased risk of infants with low blood sugar levels (hypoglycemia) .
HbA1c is a good predictor of congenital malformations. The rate of congenital malformations among those who had HbA1c in a diabetic range, pre-diabetic range or normal range was 27.8%, 9.8% and 3.0%, respectively .
Post-partum Weight Loss in Diabetic Women
Pre-pregnancy BMI and weight retention after delivery were positively associated with HbA1c levels during the first year after delivery in women with Type 1 diabetes. Interventions to modify the behaviors associated with these bodyweight factors before pregnancy and after delivery may help women with Type 1 diabetes maintain good blood sugar and HbA1c levels after pregnancy .
Other Blood Markers Linked with HbA1c to Check
Conversely, in patients with type 1 diabetes, an association between elevated blood adiponectin concentration and high HbA1c has been reported .
More studies are needed to clarify the relationship between adiponectin and HbA1c.
2) Thyroid Hormone
Also, the thyroid hormone increases the production of new red blood cells, another condition that results in lower HbA1c .
Irregular HbA1c Levels?
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HbA1c is a measure of your average blood glucose levels over the past 3 months. The test is simple, quick, and you don’t need to prepare for it. Doctors usually order the HbA1c test to check for or monitor prediabetes or diabetes.
Healthy people should keep their levels in the normal range, which is 4-5.6%. Slightly higher levels point to prediabetes, while high levels (above 6.5%) indicate diabetes. However, your doctor can’t diagnose diabetes without also running a glucose test.
If you have diabetes, keep your HbA1c levels stable and as low as possible. You won’t need to check them more than twice a year.
HbA1c may slightly vary depending on the season (higher in warm months), a person’s ethnicity, gender, and genetic makeup. Levels should remain stable in a healthy pregnancy, while high HbA1c can cause problems for both the mother and baby.