For people without diabetes, the normal range for the hemoglobin A1c test is between 4% and 5.6%. Hemoglobin A1c levels between 5.7% and 6.4% indicate increased risk of diabetes, and levels of 6.5% or higher indicate diabetes.

HbA1c is a term commonly used in relation to diabetes. This guide explains what HbA1c is, how it

differs from blood glucose levels and how it's used fordiagnosing diabetes.

What is HbA1c?The term HbA1c refers to glycated haemoglobin. It develops when haemoglobin, a protein within red

blood cells that carries oxygen throughout your body, joins with glucose in the blood, becoming

'glycated'.

By measuring glycated haemoglobin (HbA1c), clinicians are able to get an overall picture of what our

average blood sugar levels have been over a period of weeks/months.

For people with diabetes this is important as the higher the HbA1c, the greater the risk of developing

diabetes-related complications. 

HbA1c is also referred to as haemoglobin A1c or simply A1c.

1. If you had a fasting blood glucose test: A level of 100 to 125 mg/dL means you have impaired fasting glucose, a type of prediabetes. This increases your risk of developing type 2 diabetes. A level of 126 mg/dL and higher usually means you have diabetes.

A blood glucose test measures the amount of a sugar called glucose in a sample of your blood.

Glucose is a major source of energy for most cells of the body, including brain cells. Carbohydrates

are found in fruit, cereal, bread, pasta, and rice. They are quickly turned into glucose in your body.

This raises your blood glucose level.

Hormones made in the body help control blood glucose levels.

If your blood glucose measures 126 mg/dL or higher, your doctor will order a second test. If a second

test done on a different day also measures 126 mg/dL or higher, you have diabetes, and you don't need

any further tests to diagnose it.

If your blood glucose measures 100 mg/dL to 125 mg/dL, your doctor will recommend another blood

test. You have higher-than-normal blood glucose levels, but the levels are not high enough to be

diagnosed as having diabetes.  Your doctor will confirm all abnormal tests with a second test before

diagnosing diabetes.

Screening and Diagnosis

The following tests may be used for screening and diagnosis of type 1, type 2 or prediabetes. (Gestational diabetes

testing is different—see below.) If the initial screening result from one of the tests is abnormal, the test is repeated on

another day. The repeat result must also be abnormal to confirm a diagnosis of diabetes.

Fasting glucose (fasting blood glucose, FBG) – this test measures the level of glucose in the blood after fasting

for at least 8 hours.

2-hour glucose tolerance test (GTT) – for this test, the person has a fasting glucose test done (see above), then

drinks a 75-gram glucose drink. Another blood sample is drawn 2 hours after the glucose drink. This protocol

"challenges" the person's body to process the glucose. Normally, the blood glucose level rises after the drink

and stimulates the pancreas to release insulin into the bloodstream. Insulin allows the glucose to be taken up by

cells. As time passes, the blood glucose level is expected to decrease again. When a person is unable to

produce enough insulin, or if the body's cells are resistant to its effects (insulin resistance), then less glucose is

transported from the blood into cells and the blood glucose level remains high.

A different test called hemoglobin A1c may be used as an alternative to glucose testing for screening and

diagnosis. (For more, see the article on A1c.).

What Abnormal Results MeanIf you had a fasting blood glucose test:

A level of 100 to 125 mg/dL means you have impaired fasting glucose, a type of

prediabetes. This increases your risk of developing type 2 diabetes.

A level of 126 mg/dL and higher usually means you have diabetes.

If you had a random blood glucose test:

A level of 200 mg/dL or higher often means you have diabetes.

Your health care provider will order a fasting blood glucose, HbA1c test, or glucose

tolerance test, depending on your random blood glucose test result.

In someone who has diabetes, an abnormal result on the random blood glucose

test may mean that the diabetes is not well controlled. 

A 2-hour post-prandial blood sugar (glucose) test measures the blood sugar exactly 2

hours after the start of a meal. Blood sugar tests may be used to check for diabetes and

to see how treatment for diabetes is working.

Diabetes may be diagnosed if the 2-hour post-prandial blood sugar level is higher than

normal for a person's age. This is true especially if the test on two different days gives

the same results and the person has symptoms of diabetes.

This is a blood test to check for diabetes. If you have diabetes, your body doesn't make enough insulin to keep your blood sugar in check. This means your blood sugar levels are too high, and over time this can lead to serious health problems including nerve and eye damage.

This test is done to see how your body responds to sugar and starch after you eat a meal. As you digest the food in your stomach, blood glucose, or blood sugar, levels rise sharply. In response, your pancreas releases insulin to help move these sugars from the blood into the cells of muscles and other tissues to be used for fuel. Within two hours of eating, your insulin and blood glucose levels should return to normal. If your blood glucose levels remain high, you may have diabetes. 

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Test results vary by age and are usually measured in milligrams per deciliter (mg/dL). Normal results for the two-hour postprandial test based on age are:

Newborn to 50 years: less than 140 mg/dL 50 to 60 years: less than 150 mg/dL 60 years and older: less than 160 mg/dL

A normal result for the one-hour glucose screen for gestational diabetes is less than 140 mg/dL.

If your blood glucose level is still high two hours after you've eaten, or if it is high one hour after a gestational diabetes glucose tolerance test, it could be a sign that you have an insulin-related problem.  

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. A blood sample is taken before you eat, to provide a baseline, and then again two hours after you've eaten.

If you are having the glucose test for gestational diabetes, you will first be given a sugary drink. 

1. T3 tests, which check for levels of triiodothyronine, are usually ordered if T4 tests and TSH tests suggest hyperthyroidism. The T3 test may also be ordered if you are

showing signs of an overactive thyroid gland. The normal range for the T3 is 100-200 nanograms of hormone per deciliter of blood.Jul 18, 2012

2. Blood tests to measure TSH, T4, T3 and Free T4 are readily available and widely used.

Tests to evaluate thyroid function include the following:

3. TSH TESTS

The best way to initially test thyroid function is to measure the TSH level in a blood sample.

A high TSH level indicates that the thyroid gland is failing because of a problem that is

directly affecting the thyroid (primary hypothyroidism). The opposite situation, in which the

TSH level is low, usually indicates that the person has an overactive thyroid that is producing

too much thyroid hormone (hyperthyroidism). Occasionally, a low TSH may result from an

abnormality in the pituitary gland, which prevents it from making enough TSH to stimulate the

thyroid (secondary hypothyroidism). In most healthy individuals, a normal TSH value means

that the thyroid is functioning normally.

 

 

When thyroid hormone levels in the blood are low, the pituitary releases more TSH.  When thyroid hormone levels are high, the pituitary decreases TSH production.

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Why do health care providers perform thyroid tests?Health care providers perform thyroid tests to assess how well the thyroid is working.  The tests are also used to diagnose and help find the cause of thyroid disorders such as hyperthyroidism and hypothyroidism:

Hyperthyroidism is a disorder caused by too much thyroid hormone in the bloodstream, which increases the speed of bodily functions and leads to weight loss, sweating, rapid heart rate, and high blood pressure, among other symptoms.

Hypothyroidism is a disorder that occurs when the thyroid doesn’t make enough thyroid hormone for the body’s needs.  Without enough thyroid hormone, many of the body’s functions slow down.  People may have symptoms such as fatigue, weight gain, and cold intolerance.

Read more about thyroid disorders in Hyperthyroidism and Hypothyroidism at www.endocrine.niddk.nih.govExternal NIDDK Link.

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What blood tests do health care providers use to check a person’s thyroid function?A health care provider may order several blood tests to check thyroid function, including the following:

TSH test T4 tests T3 test thyroid-stimulating immunoglobulin (TSI) test antithyroid antibody test, also called the thyroid peroxidase antibody test (TPOab)

A blood test involves drawing blood at a health care provider’s office or a commercial facility and sending the sample to a lab for analysis.  Blood tests assess thyroid function by measuring TSH and thyroid hormone levels, and by detecting certain autoantibodies present in autoimmune thyroid disease.  Autoantibodies are molecules produced by a person’s body that mistakenly attack the body’s own tissues.

Many complex factors affect thyroid function and hormone levels. Health care providers take a patient’s full medical history into account when interpreting thyroid function tests.

TSH Test

A health care provider usually performs the TSH blood test first to check how well the thyroid is working.  The TSH test measures the amount of TSH a person’s pituitary is secreting.  The TSH test is the most accurate test for diagnosing both hyperthyroidism and hypothyroidism.  Generally, a below-normal level of TSH suggests hyperthyroidism.  An abnormally high TSH level suggests hypothyroidism.

The TSH test detects even tiny amounts of TSH in the blood. Normally, the pituitary boosts TSH production when thyroid hormone levels in the blood are low.  The thyroid responds by making more hormone.  Then, when the body has enough thyroid hormone circulating in the blood, TSH output drops.  The cycle repeats continuously to maintain a healthy level of thyroid hormone in the body. In people whose thyroid produces too much thyroid hormone, the pituitary shuts down TSH production, leading to low or even undetectable TSH levels in the blood.

In people whose thyroid is not functioning normally and produces too little thyroid hormone, the thyroid cannot respond normally to TSH by producing thyroid hormone.  As a result, the pituitary keeps making TSH, trying to get the thyroid to respond.

If results of the TSH test are abnormal, a person will need one or more additional tests to help find the cause of the problem.

T4 Tests

The thyroid primarily secretes T4 and only a small amount of T3. T4 exists in two forms:

T4 that is bound to proteins in the blood and is kept in reserve until needed a small amount of unbound or “free” T4 (FT4), which is the active form of the hormone and is

available to enter body tissues when needed

A high level of total T4—bound and FT4 together—or FT4 suggests hyperthyroidism, and a low level of total T4 or FT4suggests hypothyroidism.

Both pregnancy and taking oral contraceptives increase levels of binding protein in the blood.  In either of these cases, although a woman may have a high total T4 level, she may not have hyperthyroidism.  Severe illness or the use of corticosteroids—a class of medications that treat asthma, arthritis, and skin conditions, among other health problems—can decrease binding protein levels. Therefore, in these cases, the total T4 level may be low, yet the person does not have hypothyroidism.

T3 Test

If a health care provider suspects hyperthyroidism in a person who has a normal FT4 level, a T3 test can be useful to confirm the condition.  In some cases of hyperthyroidism, FT4 is normal yet free T3 (FT3) is elevated, so measuring both T4and T3 can be useful if a health care provider suspects hyperthyroidism.  The T3 test is not useful in diagnosing hypothyroidism because levels are not reduced until the hypothyroidism is severe.

TSI Test

Thyroid-stimulating immunoglobulin is an autoantibody present in Graves’ disease. TSI mimics TSH by stimulating the thyroid cells, causing the thyroid to secrete extra hormone.  The TSI test detects TSI circulating in the blood and is usually measured

in people with Graves’ disease when the diagnosis is obscure during pregnancy to find out if a person is in remission, or no longer has hyperthyroidism and its symptoms

Antithyroid Antibody Test

Antithyroid antibodies are markers in the blood that are extremely helpful in diagnosing Hashimoto’s disease.  Two principal types of antithyroid antibodies are

anti-TG antibodies, which attack a protein in the thyroid called thyroglobulin anti-thyroperoxidase, or anti-TPO, antibodies, which attack an enzyme in thyroid cells called

thyroperoxidase

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What do thyroid test results tell health care providers?Health care providers look at thyroid test results in people with hyperthyroidism or hypothyroidism to find the underlying cause of their thyroid disorder.  The following tables illustrate what test results may show based on the type of thyroid problem.

Table 1. Typical thyroid function test results:Hyperthyroidism

Cause

Test

TSH T3/T4 TSIRadioactive Iodine          Uptake Test

Graves' disease ↓ ↑ + ↑

Thyroiditis (with hyperthyroidism) ↓ ↑ - ↓

Thyroid nodules (hot, or toxic) ↓ ↑ - ↑ or Normal

Key:   ↑  = Above Normal     ↓  = Below Normal     +  = Positive     −  = Negative

Table 2. Typical thyroid function test results:Hypothyroidism

Cause

Test

TSH T3/T4 Antithyroid Antibody

Hashimoto’s disease (thyroiditis, early stage) ↑ ↓ or Normal +

Hashimoto’s disease (thyroiditis, later stage) ↑ ↓ +

Pituitary abnormality ↓ ↓ -

Key:   ↑  = Above Normal     ↓  = Below Normal     +  = Positive     − = Negative

A blood draw, also known as venipuncture, is an outpatient procedure performed at a lab or a doctor’s office. When you arrive for the test, you will be asked to sit in a comfortable chair or lie down on a cot or gurney. If you are wearing long sleeves, you will be asked to roll one sleeve up or to remove your arm from the sleeve.

A technician (or nurse) will tie a band of rubber tightly around your upper arm to make the veins swell with blood. Once the technician has found an appropriate vein, he or she will insert a needle under the skin and into the vein. You may feel a sharp prick when the needle punctures the skin. The technician will collect blood in test tubes and send it to a laboratory for analysis.

When the technician has gathered the amount of blood needed for the test or tests, he or she will withdraw the needle and place pressure on the puncture wound

until the bleeding stops. The technician will then place a small bandage over the wound.