The A1C test is a blood test that provides your average levels of blood glucose over the past 3 months. Learn how the A1C test works, how it is used to diagnose and monitor type 2 diabetes and prediabetes, when it doesn’t work, and how A1C relates to estimated average glucose (eAG).
Hemoglobin A1C
Image by AdamStanislav
What Is A1C?
What is Diabetes
Video by Centers for Disease Control and Prevention (CDC)/YouTube
What is Diabetes
Video by Centers for Disease Control and Prevention (CDC)/YouTube
A1C
A1C is a blood test for type 2 diabetes and prediabetes. It measures your average blood glucose, or blood sugar, level over the past 3 months. Doctors may use the A1C alone or in combination with other diabetes tests to make a diagnosis. They also use the A1C to see how well you are managing your diabetes. This test is different from the blood sugar checks that people with diabetes do every day.
Your A1C test result is given in percentages. The higher the percentage, the higher your blood sugar levels have been:
A normal A1C level is below 5.7 percent
Prediabetes is between 5.7 to 6.4 percent. Having prediabetes is a risk factor for getting type 2 diabetes. People with prediabetes may need retests every year.
Type 2 diabetes is above 6.5 percent
If you have diabetes, you should have the A1C test at least twice a year. The A1C goal for many people with diabetes is below 7. It may be different for you. Ask what your goal should be. If your A1C result is too high, you may need to change your diabetes care plan.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Additional Materials (22)
Hemoglobin A1C Molecule
Hemoglobin is a protein found inside red blood cells that carries oxygen from the lungs to cells throughout the body. Hemoglobin also binds with glucose. Diabetics have too much glucose in the bloodstream and this extra glucose binds (or glycates) with hemoglobin. Glycated hemoglobin usually stays glycated for the life of the red blood cell (about 3 months). Therefore, the percentage of hemoglobin that is glycated (measured as A1C) reflects glucose levels that have affected red blood cells up to 3 months in the past.
Image by TheVisualMD
Preventing or Delaying the Onset of Type 2 Diabetes
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Preventing Pre-Diabetes
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Hemoglobin A1c & Diabetes
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Dr. Sarah Hallberg: What's the cause of insulin resistance?
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Interpreting A1C: Principles of the A1C Assay
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What Is An A1C?
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Understanding Your A1C (Conditions A-Z)
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A1C Levels
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Is Your A1C AOK?
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A1c - What You Need To Know
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Diabetes & Gum Disease are Connected!
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Teen Diabetes Type 1& 2
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Guide to type 1 diabetes - English
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Hemoglobin A1C Molecule
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Interpreting A1C: Principles of the A1C Assay
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Understanding Your A1C (Conditions A-Z)
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The 411 On Your A1c
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Is Your A1C AOK?
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A1c - What You Need To Know
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Type 1 diabetes breakthrough is 'significant step forward'
The Telegraph/YouTube
What Is the A1C Test?
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Hemoglobin A1c
Video by TheVisualMD
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Hemoglobin A1c
The hemoglobin A1c test measures the percentage of hemoglobin bound to blood sugar (glucose); the test is used to diagnose type 1 and type 2 diabetes. Because the test results reflect average blood sugar levels over a period of 2-3 months (rather than daily fluctuations), the hemoglobin A1C test is also used to gauge how well patients are managing their diabetes over time.
Video by TheVisualMD
What Is the A1C Test?
The A1C test is a blood test that provides information about your average levels of blood glucose, also called blood sugar, over the past 3 months. The A1C test can be used to diagnose type 2 diabetes and prediabetes. The A1C test is also the primary test used for diabetes management.
The A1C test is sometimes called the hemoglobin A1C, HbA1c, glycated hemoglobin, or glycohemoglobin test. Hemoglobin is the part of a red blood cell that carries oxygen to the cells. Glucose attaches to or binds with hemoglobin in your blood cells, and the A1C test is based on this attachment of glucose to hemoglobin.
The higher the glucose level in your bloodstream, the more glucose will attach to the hemoglobin. The A1C test measures the amount of hemoglobin with attached glucose and reflects your average blood glucose levels over the past 3 months.
The A1C test result is reported as a percentage. The higher the percentage, the higher your blood glucose levels have been. A normal A1C level is below 5.7 percent.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Hemoglobin A1C Test
Hemoglobin A1C Test
Also called: A1C test, HbA1c, Glycohemoglobin, Glycated hemoglobin, Glycosylated hemoglobin
A hemoglobin A1C test is a blood test that measures the amount of glucose (sugar) attached to hemoglobin. An A1C test can show your average glucose level for the past three months. Doctors may use the A1C alone or in combination with other diabetes tests to make a diagnosis. They also use the A1C to see how well you are managing your diabetes.
Hemoglobin A1C Test
Also called: A1C test, HbA1c, Glycohemoglobin, Glycated hemoglobin, Glycosylated hemoglobin
A hemoglobin A1C test is a blood test that measures the amount of glucose (sugar) attached to hemoglobin. An A1C test can show your average glucose level for the past three months. Doctors may use the A1C alone or in combination with other diabetes tests to make a diagnosis. They also use the A1C to see how well you are managing your diabetes.
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A hemoglobin A1C (HbA1C) test is a blood test that shows what your average blood sugar (glucose) level was over the past two to three months.
Glucose is a type of sugar in your blood that comes from the foods you eat. Your cells use glucose for energy. A hormone called insulin helps glucose get into your cells. If you have diabetes your body doesn't make enough insulin, or your cells don't use it well. As a result, glucose can't get into your cells, so your blood sugar levels increase.
Glucose in your blood sticks to hemoglobin, a protein in your red blood cells. As your blood glucose levels increase, more of your hemoglobin will be coated with glucose. An A1C test measures the percentage of your red blood cells that have glucose-coated hemoglobin.
An A1C test can show your average glucose level for the past three months because:
Glucose sticks to hemoglobin for as long as the red blood cells are alive.
Red blood cells live about three months.
High A1C levels are a sign of high blood glucose from diabetes. Diabetes can cause serious health problems, including heart disease, kidney disease, and nerve damage. But with treatment and lifestyle changes, you can control your blood glucose levels.
An A1C test may be used to screen for or diagnose:
Type 2 diabetes. With type 2 diabetes your blood glucose gets too high because your body doesn't make enough insulin to move blood sugar from your bloodstream into your cells, or because your cells stop responding to insulin.
Prediabetes. Prediabetes means that your blood glucose levels are higher than normal, but not high enough to diagnosed as diabetes. Lifestyle changes, such as healthy eating and exercise, may help delay or prevent prediabetes from becoming type 2 diabetes.
If you have diabetes or prediabetes, an A1C test can help monitor your condition and check how well you've been able to control your blood sugar levels.
The Centers for Disease Control (CDC) recommends A1C testing for diabetes and prediabetes if:
You are over age 45.
If your results are normal, you should repeat the test every 3 years.
If your results show you have prediabetes, you will usually need to be tested every 1 to 2 years. Ask your provider how often to get tested and what you can do to reduce your risk of developing diabetes.
If your results show you have diabetes, you should get an A1C test at least twice a year to monitor your condition and treatment.
You are under 45 and are more likely to develop diabetes because you:
Have prediabetes.
Are overweight or have obesity.
Have a parent or sibling with type 2 diabetes.
Have high blood pressure or high cholesterol levels.
Have heart disease or have had a stroke.
Are physically active less than 3 times a week.
Have had gestational diabetes (diabetes during pregnancy) or given birth to a baby over 9 pounds.
Are African American, Hispanic or Latino, American Indian, or an Alaska Native person. Some Pacific Islander and Asian American people also have a higher risk of developing diabetes.
Have polycystic ovarian syndrome (PCOS).
You may also need an A1C test if you have symptoms of diabetes, such as:
Feeling very thirsty
Urinating (peeing) a lot
Losing weight without trying
Feeling very hungry
Blurred vision
Numb or tingling hands or feet
Fatigue
Dry skin
Sores that heal slowly
Having more infections than usual
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
You don't need any special preparations for an A1C test.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
A1C results tell you what percentage of your hemoglobin is coated with glucose. The percent ranges are just a guide to what is normal. What's normal for you depends on your health, age, and other factors. Ask your provider what A1C percentage is healthy for you.
To diagnose diabetes or prediabetes, the percentages commonly used are:
Normal: A1C below 5.7%
Prediabetes: A1C between 5.7% and 6.4%
Diabetes: A1C of 6.5% or higher
Providers often use more than one test to diagnose diabetes. So, if your test result was higher than normal, you may have another A1C test or a different type of diabetes test, usually either a fasting blood glucose test or an oral glucose tolerance test (OGTT).
If your A1C test was done to monitor your diabetes, talk with your provider about what your test results mean.
The A1C test is not used to diagnose gestational diabetes or type 1 diabetes.
Also, if you have a condition that affects your red blood cells, such as anemia or another type of blood disorder, an A1C test may not be accurate for diagnosing diabetes. Kidney failure and liver disease can also affect A1C results. In these cases, your provider may recommend different tests to diagnose diabetes and prediabetes.
Hemoglobin A1C (HbA1c) Test: MedlinePlus Medical Test [accessed on Oct 05, 2022]
https://diabetesed.net/wp-content/uploads/2017/12/2018-ADA-Standards-of-Care.pdf [accessed on Apr 19, 2019]
https://labtestsonline.org/tests/hemoglobin-a1c [accessed on Apr 19, 2019]
https://www.niddk.nih.gov/health-information/diabetes/overview/tests-diagnosis/a1c-test [accessed on Apr 19, 2019]
Normal reference ranges can vary depending on the laboratory and the method used for testing. You must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."
Additional Materials (24)
Hemoglobin A1C molecule
Hemoglobin is a protein found inside red blood cells that carries oxygen from the lungs to cells throughout the body. Hemoglobin also binds with glucose. Diabetics have too much glucose in the bloodstream and this extra glucose binds (or glycates) with hemoglobin. Glycated hemoglobin usually stays glycated for the life of the red blood cell (about 3 months). Therefore, the percentage of hemoglobin that is glycated (measured as A1C) reflects glucose levels that have affected red blood cells up to 3 months in the past.
Image by TheVisualMD
Hemoglobin A1C: Red Blood Cells
Red blood cells use the iron-rich protein hemoglobin to carry oxygen from the lungs to cells throughout the body and return carbon dioxide to the lungs. The percentage of hemoglobin bound to blood glucose (hemoglobin A1C) is used to diagnose diabetes.
Image by TheVisualMD
Testing and Diagnosing Diabetes
Several tests are used to diagnose prediabetes and diabetes. In June 2009, the ADA, the European Association for the Study of Diabetes, and the International Diabetes Federation made a joint recommendation that type 2 diabetes testing include the glycated hemoglobin (A1C) test. This test measures average blood glucose level during the past 2-3 months by measuring the percentage of glucose attached to hemoglobin, the oxygen-carrying protein pigment in red blood cells.
Image by TheVisualMD
HemoglobinA1C molecule
The A1C test is a common blood test used to diagnose type 1 and type 2 diabetes and then to gauge how well you're managing your diabetes. The A1C test goes by many other names, including glycated hemoglobin, glycosylated hemoglobin, hemoglobin A1C and HbA1c. The A1C test result reflects your average blood sugar level for the past two to three months. Specifically, the A1C test measures what percentage of your hemoglobin, a protein in red blood cells that carries oxygen, is coated with sugar (glycated). The higher your A1C level, the poorer your blood sugar control. And if you have previously diagnosed diabetes, the higher the A1C level, the higher your risk of diabetes complications.
Image by TheVisualMD
α,β-hemoglobin/haptoglobin hexamer complex
A model of α,β-hemoglobin/haptoglobin hexamer complex. There are 2 α,β-hemoglobin dimers depicted: one space filling model (yellow/orange), and one ribbon model (purple/blue). Each is bound by a haptoglobin molecule (both haptoglobin molecules are shown in pink, with one as a space filling model and one as a ribbon model).
Image by Ayacop
Hemoglobin, Carbon Monoxide
Hemoglobin is an iron-containing protein that enables red blood cells to deliver oxygen from the lungs to cells throughout the body. But the same binding site on the hemoglobin molecule has an even stronger affinity for carbon monoxide, which is why we are so susceptible to poisoning by this deadly gas; carbon monoxide grabs all the binding sites and starves the body's tissues of oxygen
Image by TheVisualMD
This browser does not support the video element.
Hemoglobin A1c
The hemoglobin A1c test measures the percentage of hemoglobin bound to blood sugar (glucose); the test is used to diagnose type 1 and type 2 diabetes. Because the test results reflect average blood sugar levels over a period of 2-3 months (rather than daily fluctuations), the hemoglobin A1C test is also used to gauge how well patients are managing their diabetes over time.
Video by TheVisualMD
Understanding Your A1C (Conditions A-Z)
Video by Healthguru/YouTube
Haemoglobin
Video by Wellcome Trust/YouTube
A1c - What You Need To Know
Video by Rehealthify/YouTube
This browser does not support the video element.
Type 2 Diabetes Testing
An estimated 79 million Americans, just over 25 percent of the population aged 20 years or older, have prediabetes. Prediabetes is a state where blood sugars may be a little bit elevated, but are not yet elevated to a dangerous range. It is typically asymptomatic, and if undiagnosed and untreated, prediabetes may lead to a potentially life-threatening condition called type 2 diabetes. Complications of type 2 diabetes include blindness, heart attack, and stroke. Prediabetes is readily detectable through simple blood testing with a goal of detecting abnormal glucose levels. Two common and complementary tests include fasting blood sugar and hemoglobin A1C (HbA1c) tests. With early detection and diagnosis, appropriate and immediate action can be made by the patient to reduce complications and to ensure a long and healthy life.
Video by TheVisualMD
Diagnosis of Type 2 Diabetes
Video by Animated Diabetes Patient/YouTube
Hemoglobin A1c & Diabetes
Video by DiabeTV/YouTube
Diabetic HbA1c - Everything You Need To Know - Dr. Nabil Ebraheim
Video by nabil ebraheim/YouTube
What Is An A1C?
Video by dLife/YouTube
A1C Levels
Video by Khan Academy/YouTube
This browser does not support the video element.
Type 1 Diabetes Diagnosis & Treatment
Type 1 diabetes can be diagnosed with blood tests that measure how much sugar is in your blood. They include: hemoglobin A1C, fasting blood glucose, and oral glucose tolerance. Type 1 diabetes is usually diagnosed in childhood or adolescence. About 5% of adults with diabetes have type 1 diabetes. Early diagnosis is crucial for early treatment. Type 1 diabetics need to take insulin, either through a pump or injections. Regular exercise as well as a diet low in refined carbohydrates will also help control blood sugar levels. By maintaining appropriate blood sugar levels, type 1 diabetics can lead normal lives free of serious complications.
Video by TheVisualMD
The 411 On Your A1c
Video by Lee Health/YouTube
Is Your A1C AOK?
Video by Lee Health/YouTube
What if the root cause of type 2 diabetes is found in the gut rather than the pancreas?
Video by TEDMED/YouTube
Lactate Threshold Test
Video by Mount Sinai Health System/YouTube
How HbA1c testing detects glucose in your body for diabetes type 2
Video by Pathology Tests Explained/YouTube
A Critical Balance
Key Players
The Fuel Supply Chain
Diabetes Symptoms
Overweight
Diabetes and Large Vessel Disease
Diabetes and Small Vessel Disease
Nerve Damage
Testing and Diagnosis
Keep It Down
Health in Action
Put Out the Fire
Calming Diabetes
Keeping Tabs on Glucose
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Diabetes in the US
Interactive by TheVisualMD
Hemoglobin A1C molecule
TheVisualMD
Hemoglobin A1C: Red Blood Cells
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Testing and Diagnosing Diabetes
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HemoglobinA1C molecule
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α,β-hemoglobin/haptoglobin hexamer complex
Ayacop
Hemoglobin, Carbon Monoxide
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0:27
Hemoglobin A1c
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Understanding Your A1C (Conditions A-Z)
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Haemoglobin
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A1c - What You Need To Know
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Type 2 Diabetes Testing
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Diagnosis of Type 2 Diabetes
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Hemoglobin A1c & Diabetes
DiabeTV/YouTube
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Diabetic HbA1c - Everything You Need To Know - Dr. Nabil Ebraheim
nabil ebraheim/YouTube
3:03
What Is An A1C?
dLife/YouTube
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A1C Levels
Khan Academy/YouTube
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Type 1 Diabetes Diagnosis & Treatment
TheVisualMD
1:56
The 411 On Your A1c
Lee Health/YouTube
1:41
Is Your A1C AOK?
Lee Health/YouTube
3:21
What if the root cause of type 2 diabetes is found in the gut rather than the pancreas?
TEDMED/YouTube
1:06
Lactate Threshold Test
Mount Sinai Health System/YouTube
2:28
How HbA1c testing detects glucose in your body for diabetes type 2
Pathology Tests Explained/YouTube
Diabetes in the US
TheVisualMD
Why Should I Get the A1C Test?
Blood Sugar Gone Awry
Image by TheVisualMD
Blood Sugar Gone Awry
We are made entirely of cells, and the cells of the body depend on sugar in the blood, derived from carbohydrates, for food and energy. Allowing for the innumerable differences among individuals, the threshold for a normal blood-sugar (glucose) level in healthy people is 100 mg/dL; that is, 100 milligrams of glucose per deciliter of blood. Lower-than-normal levels characterize hypoglycemia and higher than normal levels hyperglycemia. Hypoglycemia, indicated around 70 mg/dL and lower, can be traced to three causes. The body may be using up the available blood sugar (glucose), or the glucose ingested may be released into the blood stream too slowly. It's also possible that too much insulin is being released. Hyperglycemia is the hallmark of prediabetes (between 100 and 125 mg/dL) and diabetes (126 mg/dL and higher). It is caused by either too little insulin being released by the pancreas or the body`s inability to use insulin properly.
Image by TheVisualMD
Why Should a Person Get the A1C Test?
Testing can help health care professionals
find prediabetes and counsel you about lifestyle changes to help you delay or prevent type 2 diabetes
find type 2 diabetes
work with you to monitor the disease and help make treatment decisions to prevent complications
If you have risk factors for prediabetes or diabetes, talk with your doctor about whether you should be tested.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
How Is It Used to Diagnose Diabetes?
A1C
Image by AdamStanislav
A1C
Image by AdamStanislav
How Is the A1C Test Used to Diagnose Type 2 Diabetes and Prediabetes?
Health care professionals can use the A1C test alone or in combination with other diabetes tests to diagnose type 2 diabetes and prediabetes. You don’t have to fast before having your blood drawn for an A1C test, which means that blood can be drawn for the test at any time of the day.
If you don’t have symptoms but the A1C test shows you have diabetes or prediabetes, you should have a repeat test on a different day using the A1C test or one of the other diabetes tests to confirm the diagnosis.
A1C results and what the numbers mean
*Any test used to diagnose diabetes requires confirmation with a second measurement, unless there are clear symptoms of diabetes.
Diagnosis*
A1C Level
Normal
below 5.7 percent
Prediabetes
5.7 to 6.4 percent
Diabetes
6.5 percent or above
When using the A1C test for diagnosis, your doctor will send your blood sample taken from a vein to a lab that uses an NGSP-certified method. The NGSP, formerly called the National Glycohemoglobin Standardization Program, certifies that makers of A1C tests provide results that are consistent and comparable with those used in the Diabetes Control and Complications Trial.
Blood samples analyzed in a doctor’s office or clinic, known as point-of-care tests, should not be used for diagnosis.
The A1C test should not be used to diagnose type 1 diabetes, gestational diabetes, or cystic fibrosis-related diabetes. The A1C test may give false results in people with certain conditions.
Having prediabetes is a risk factor for developing type 2 diabetes. Within the prediabetes A1C range of 5.7 to 6.4 percent, the higher the A1C, the greater the risk of diabetes.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Additional Materials (3)
A1C test for diabetes C prediabetes
Video by NIH Clinical Center/YouTube
Hemoglobin A1c & Diabetes
Video by DiabeTV/YouTube
A1C Levels
Video by Khan Academy/YouTube
2:26
A1C test for diabetes C prediabetes
NIH Clinical Center/YouTube
1:43
Hemoglobin A1c & Diabetes
DiabeTV/YouTube
6:09
A1C Levels
Khan Academy/YouTube
Is It Used in Pregnancy?
Pregnant Woman With Diabetes Concerns
Image by TheVisualMD
Pregnant Woman With Diabetes Concerns
Pregnant Woman With Diabetes Concerns.jpg
Image by TheVisualMD
Is the A1C Test Used During Pregnancy?
Health care professionals may use the A1C test early in pregnancy to see if a woman with risk factors had undiagnosed diabetes before becoming pregnant. Since the A1C test reflects your average blood glucose levels over the past 3 months, testing early in pregnancy may include values reflecting time before you were pregnant. The glucose challenge test or the oral glucose tolerance test (OGTT) are used to check for gestational diabetes, usually between 24 and 28 weeks of pregnancy. If you had gestational diabetes, you should be tested for diabetes no later than 12 weeks after your baby is born. If your blood glucose is still high, you may have type 2 diabetes. Even if your blood glucose is normal, you still have a greater chance of developing type 2 diabetes in the future and should get tested every 3 years.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Can Other Blood Glucose Tests Be Used?
Blood Glucose and Baselining Your Health
Image by TheVisualMD
Blood Glucose and Baselining Your Health
Our bodies and brains run on glucose, a simple sugar produced by the digestion of carbohydrates. The body's ability to use glucose depends on the hormone insulin, which is produced by the pancreas. Blood sugar levels naturally rise after meals, but insulin from a healthy pancreas keeps these levels within a narrow range. In diabetes, however, this balance is disrupted because either the body loses its ability to respond to insulin or the pancreas loses its ability to produce insulin. Too much or too little glucose in the bloodstream can damage blood vessels in the kidneys and eyes, as well as nerve cells; acute disruptions of the insulin/glucose balance can be life threatening. Blood and urine tests can determine whether someone is diabetic or pre-diabetic. Diabetes is looming as a major public health concern; an estimated 25 million people in the U.S. have diabetes, with more than a quarter of them undiagnosed.
Image by TheVisualMD
Can Other Blood Glucose Tests Be Used to Diagnose Type 2 Diabetes and Prediabetes?
Yes. Health care professionals also use the fasting plasma glucose (FPG) test and the OGTT to diagnose type 2 diabetes and prediabetes. For these blood glucose tests used to diagnose diabetes, you must fast at least 8 hours before you have your blood drawn. If you have symptoms of diabetes, your doctor may use the random plasma glucose test, which doesn’t require fasting. In some cases, health care professionals use the A1C test to help confirm the results of another blood glucose test.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Can the A1C Test Result in a Different Diagnosis?
A1C blood test
Image by jaytaix/Pixabay
A1C blood test
Image by jaytaix/Pixabay
Can the A1C Test Result in a Different Diagnosis Than the Blood Glucose Tests?
Yes. In some people, a blood glucose test may show diabetes when an A1C test does not. The reverse can also occur—an A1C test may indicate diabetes even though a blood glucose test does not. Because of these differences in test results, health care professionals repeat tests before making a diagnosis.
People with differing test results may be in an early stage of the disease, when blood glucose levels have not risen high enough to show up on every test. In this case, health care professionals may choose to follow the person closely and repeat the test in several months.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Why Do Diabetes Blood Test Results Vary?
Glucose Control
Image by TheVisualMD
Glucose Control
Many people with type 2 diabetes find that losing weight, eating the right foods, and increasing their level of activity are enough to keep their blood glucose levels under control. But if lifestyle changes don`t have the effect of normalizing blood glucose levels, then medications may be prescribed. Medications to treat or prevent specific complications may also be given. If both lifestyle changes and oral glucose-lowering medications prove ineffective, then insulin may be prescribed as well.
Image by TheVisualMD
Why Do Diabetes Blood Test Results Vary?
Lab test results can vary from day to day and from test to test. This can be a result of the following factors:
Blood glucose levels move up and down
Your results can vary because of natural changes in your blood glucose level. For example, your blood glucose level moves up and down when you eat or exercise. Sickness and stress also can affect your blood glucose test results. A1C tests are less likely to be affected by short-term changes than FPG or OGTT tests.
The following chart shows how multiple blood glucose measurements over 4 days compare with an A1C measurement.
Blood Glucose Measurements Compared with A1C Measurements over 4 Days
Blood glucose (mg/dL) measurements were taken four times per day (fasting or pre-breakfast, pre-lunch, pre-dinner, and bedtime).
The straight black line shows an A1C measurement of 7.0 percent. The blue line shows an example of how blood glucose test results might look from self-monitoring four times a day over a 4-day period.
A1C tests can be affected by changes in red blood cells or hemoglobin
Conditions that change the life span of red blood cells, such as recent blood loss, sickle cell disease, erythropoietin treatment, hemodialysis, or transfusion, can change A1C levels.
A falsely high A1C result can occur in people who are very low in iron; for example, those with iron-deficiency anemia. Other causes of false A1C results include kidney failure or liver disease.
If you’re of African, Mediterranean, or Southeast Asian descent or have family members with sickle cell anemia or a thalassemia, an A1C test can be unreliable for diagnosing or monitoring diabetes and prediabetes. People in these groups may have a different type of hemoglobin, known as a hemoglobin variant, which can interfere with some A1C tests. Most people with a hemoglobin variant have no symptoms and may not know that they carry this type of hemoglobin. Health care professionals may suspect interference—a falsely high or low result—when your A1C and blood glucose test results don’t match.
Not all A1C tests are unreliable for people with a hemoglobin variant. People with false results from one type of A1C test may need a different type of A1C test to measure their average blood glucose level. The NGSP provides information for health care professionals about which A1C tests are appropriate to use for specific hemoglobin variants.
Read about diabetes blood tests for people of African, Mediterranean, or Southeast Asian descent. The NIDDK has information for health care providers on Sickle Cell Trait & Other Hemoglobinopathies & Diabetes.
Small changes in temperature, equipment, or sample handling
Even when the same blood sample is repeatedly measured in the same lab, the results may vary because of small changes in temperature, equipment, or sample handling. These factors tend to affect glucose measurements—fasting and OGTT—more than the A1C test.
Health care professionals understand these variations and repeat lab tests for confirmation. Diabetes develops over time, so even with variations in test results, health care professionals can tell when overall blood glucose levels are becoming too high.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
How Precise Is the Test?
Diabetic tests
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Diabetic tests
Image by jaytaix/Pixabay
How Precise Is the A1C Test?
When repeated, the A1C test result can be slightly higher or lower than the first measurement. This means, for example, an A1C reported as 6.8 percent on one test could be reported in a range from 6.4 to 7.2 percent on a repeat test from the same blood sample. In the past, this range was larger but new, stricter quality-control standards mean more precise A1C test results.
Health care professionals can visit www.ngsp.org to find information about the precision of the A1C test used by their lab.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
How Is It Used After Diagnosis of Diabetes?
Testing and Diagnosis
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Testing and Diagnosis
The American Diabetes Association (ADA) recommends testing for anyone who is overweight or obese and who has one or more additional risk factors, whether or not they have symptoms. (See “Risk Factors.”) With or without risk factors and symptoms, all adults should be tested for prediabetes or diabetes starting at age 45. If the results are normal, the tests should be repeated every 3 years, but those with risk factors may need to be tested more frequently. People with prediabetes should have their blood glucose levels checked again in 1-2 years.
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How Is the A1C Test Used After Diagnosis of Diabetes?
Your health care professional may use the A1C test to set your treatment goals, modify therapy, and monitor your diabetes management.
Experts recommend that people with diabetes have an A1C test at least twice a year. Health care professionals may check your A1C more often if you aren’t meeting your treatment goals.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
What A1C Goal Should I Have?
Manage Diabetes
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Manage Diabetes
Along with lifestyle changes, regular monitoring of blood glucose levels is necessary.
Blood Pressure Reading: Photo Copyright 2006, Lemuel Cantos
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What A1C Goal Should I Have?
People will have different A1C targets, depending on their diabetes history and their general health. You should discuss your A1C target with your health care professional. Studies have shown that some people with diabetes can reduce the risk of diabetes complications by keeping A1C levels below 7 percent.
Managing blood glucose early in the course of diabetes may provide benefits for many years to come. However, an A1C level that is safe for one person may not be safe for another. For example, keeping an A1C level below 7 percent may not be safe if it leads to problems with hypoglycemia, also called low blood glucose.
Less strict blood glucose control, or an A1C between 7 and 8 percent—or even higher in some circumstances—may be appropriate in people who have
limited life expectancy
long-standing diabetes and trouble reaching a lower goal
severe hypoglycemia or inability to sense hypoglycemia (also called hypoglycemia unawareness)
advanced diabetes complications such as chronic kidney disease, nerve problems, or cardiovascular disease
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
How Does A1C Relate to eAG?
Healthy Capillary Blood Vessel
Cross-section of Healthy Capillary Blood Vessel with Normal Glucose and Insulin Levels
Cross-Section of Damaged Capillary Blood Vessel with Very High Glucose and Insulin Levels
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Healthy Capillary Blood Vessel and and Damaged Capillary Blood Vessel Caused by High Levels of Blood Glucose
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Healthy Capillary Blood Vessel
Cross-section of Healthy Capillary Blood Vessel with Normal Glucose and Insulin Levels
Cross-Section of Damaged Capillary Blood Vessel with Very High Glucose and Insulin Levels
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2
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Healthy Capillary Blood Vessel and and Damaged Capillary Blood Vessel Caused by High Levels of Blood Glucose
1) Healthy Capillary Blood Vessel - This image depicts a healthy capillary. Capillaries are the smallest blood vessels in your body. They can be so thin in diameter that blood cells have to bend in order to pass through. Capillaries are where the transfer of nutrients from the blood to cells, and the transfer of waste from cells to blood, takes place. In a healthy body, the blood vessels are smooth and elastic.
2) Cross-Section of Healthy Capillary Blood Vessel with Normal Glucose and Insulin Levels - This image depicts a healthy capillary. The body's cells depend on sugar in the blood, which is derived from carbohydrates, for food and energy. Allowing for the innumerable differences among individuals, the threshold for a normal blood sugar (glucose, pink) level in healthy people is 100 mg/dL; that is, 100 milligrams of glucose per deciliter of blood. Lower-than-normal levels characterize hypoglycemia and higher-than-normal levels characterize hyperglycemia. Without insulin (yellow), glucose is not able to enter cells to be used as fuel. Because of this, healthy insulin levels are a key factor in keeping blood glucose levels normal.
3) Cross-Section of Damaged Capillary Blood Vessel with Very High Glucose and Insulin Levels - This image depicts an unhealthy, damaged capillary with very high levels of insulin and glucose. Higher than normal levels of blood glucose lead to hyperglycemia. Hyperglycemia is the hallmark of prediabetes (between 100 and 125 mg/dL) and diabetes (126 mg/dL and higher). It is caused by either too little insulin being released by the pancreas or the body's inability to use insulin properly. Hyperglycemia leads to microangiopathy, marked by endothelial cell apoptosis (programmed cell death), accumulation of AGEs (advanced glycation end products), and thickening of the basement membrane, which can lead to the development of lesions, vasoconstriction, and altered vessel function
Interactive by TheVisualMD
How Does A1C Relate to Estimated Average Glucose?
Estimated average glucose (eAG) is calculated from your A1C. Some laboratories report eAG with A1C test results. The eAG number helps you relate your A1C to daily glucose monitoring levels. The eAG calculation converts the A1C percentage to the same units used by home glucose meters—milligrams per deciliter (mg/dL).
The eAG number will not match daily glucose readings because it’s a long-term average—rather than your blood glucose level at a single time, as is measured with a home glucose meter.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Will A1C Show Short-Term Changes?
What is insulin resistance?
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What is insulin resistance?
Insulin resistance is a condition in which the body produces insulin but does not use it effectively. When people have insulin resistance, glucose builds up in the blood instead of being absorbed by the cells, leading to type 2 diabetes or prediabetes.
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Will the A1C Test Show Short-Term Changes in Blood Glucose Levels?
Large changes in your blood glucose levels over the past month will show up in your A1C test result, but the A1C test doesn’t show sudden, temporary increases or decreases in blood glucose levels. Even though A1C results represent a long-term average, blood glucose levels within the past 30 days have a greater effect on the A1C reading than those in previous months.
Source: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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A1C and Diabetes
The A1C test is a blood test that provides your average levels of blood glucose over the past 3 months. Learn how the A1C test works, how it is used to diagnose and monitor type 2 diabetes and prediabetes, when it doesn’t work, and how A1C relates to estimated average glucose (eAG).