Diagnosis of Diabetes

Diabetes diagnosis is typically confirmed by a doctor using a blood glucose test. However, early suspicion of a possible diabetes diagnosis may arise from either its symptoms, the symptoms of its complications (e.g. leg rashes), or by a screening test.

Diagnostic Tests for Diabetes: The main diagnostic tests for diabetes include:

  • Urine glucose test. This is a test for sugar (glucose) in the urine. Normal urine does not contain glucose. High blood sugars from diabetes will cause sugar to unexpectedly appear in the urine. A positive result for sugar in the urine is a strong indicator that you have diabetes, but itís usually confirmed by a blood sugar test as well. A negative result for sugar in the urine doesnít necessarily mean that you donít have diabetes, although you probably donít have the most severe high blood sugars yet, and your doctor may still ask for a blood glucose test to fully check for diabetes. You could also still have pre-diabetes even if a urine sugar test is negative.
  • Blood glucose test (venous blood). This is the main confirmation test for diabetes. It is a full blood test, with blood drawn from a vein; it is not a finger-prick blood drop test. Your blood sugar level gives a good indication as to whether you have pre-diabetes, diabetes, or you donít have diabetes. There are also subtypes of blood glucose test, such as fasting blood glucose test versus a random blood glucose test. A fasting blood glucose test is a better test for diabetes than a random test.
  • Blood glucose finger-prick tests. These finger-prick blood tests of a blood drop for glucose levels are reasonably accurate. Your doctor might do a finger-prick test in their office, or you might also do a finger-prick test at a diabetes screening day. Depending on the level of glucose in the blood drop, it can be a strong indicator of whether you have diabetes, pre-diabetes, or no diabetes. Your doctor will usually order a full blood glucose test to confirm the results seen in a finger-prick test.

Other Blood Sugar Tests. Some of the other tests commonly used for diabetics, but not really for initial diagnosis, include:

  • HbA1c blood test. This is a form of blood glucose level test that gives a kind of average of your blood sugar levels over the last few weeks or months. Although newly diagnosed diabetics will often have a high value, this test is not really used for diagnosis of diabetes. It is mainly used for tracking long-term blood sugar control as part of managing diabetes.
  • Fructosamine test: This is another form of average blood glucose test. However, it gives an indication of blood sugar levels over a shorter period than HbA1c tests.

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Back to: « Diabetes

Diagnosis of Diabetes

If you think you might have prediabetes or diabetes, your doctor can help you decide what to do. A blood test called the A1C test can check your average blood glucose level to see if you have prediabetes.

Nathan says that people over 45 should be screened for diabetes, as should other people at increased risk.

Source: NIH News in Health (NIH)1

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How do health care providers diagnose diabetes?

The most common test for diagnosing any kind of diabetes is a one-step approach called the oral glucose tolerance test. Prior to the test, you canít eat or drink anything (except water) for between 4 and 8 hours. A health provider tests your initial sugar level and then gives you a sugar drink. Then your sugar level is checked every 30 to 60 minutes for up to 3 hours.1,2

Risk for type 1 diabetes

Health care providers can use a test to check for certain blood markers that can predict how likely it is that someone will develop type 1 diabetes. These blood markers signal that the immune system is attacking the beta cells of the pancreas. Having two or more of these markers, called antibodies, is associated with higher risk of developing type 1 diabetes over the next 10 years.3

Testing for gestational diabetes

Health care providers will consider a womanís risk factors and current health before testing for gestational diabetes. If a woman is at high risk for gestational diabetes, her health care provider will test her as soon as she knows she is pregnant. If a woman is at low risk for gestational diabetes, her health care provider might not test her at all, or will test her between 24 weeks and 28 weeks of pregnancy. For more information about testing for gestational diabetes, see the NICHDís Am I at risk for gestational diabetes? brochure.

Source: NICHD (NIH)2

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Diabetes mellitus is diagnosed, according to the WHO, by the classic symptoms of polyuria, polydipsia and unexplained weight loss, and/or a hyperglycaemia H 11.1 mmol/l (200 mg/dl) in a random sample or fasting (no caloric intake for 8 hrs), plasma glucose 7.0 mmol/l (126 mg/dl) and/or postprandial value 11.1 mmol/l (200 mg/dl) (2 hrs plasma glucose level during an oral glucose tolerance test). This test should be performed as described by the WHO, using a glucose load containing the equivalent of 75 h anhydrous glucose dissolved in water).

In the absence of unequivocal hyperglycaemia with acute metabolic decompensation, these criteria should be confirmed by repeat testing on a different day (EUDIP Definition).

Source: EC (EU)3

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Can blood glucose tests still be used for diagnosing type 2 diabetes and prediabetes?

Yes. The standard blood glucose tests used for diagnosing type 2 diabetes and prediabetes-the fasting plasma glucose (FPG) test and the OGTTóare still recommended. The random plasma glucose test, also called the casual glucose test, may be used for diagnosing diabetes when symptoms of diabetes are present. In some cases, the A1C test is used to help health care providers confirm the results of a blood glucose test.

Source: NIDDK (NIH)4

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Diabetes Tests & Diagnosis

Your health care professional can diagnose diabetes, prediabetes, and gestational diabetes through blood tests. The blood tests show if your blood glucose, also called blood sugar, is too high.

Do not try to diagnose yourself if you think you might have diabetes. Testing equipment that you can buy over the counter, such as a blood glucose meter, cannot diagnose diabetes.

Source: NIDDK (NIH)5

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Know when to check for ketones

Your doctor may want you to check your urine for ketones if you have symptoms of diabetic ketoacidosis . When ketone levels get too high, you can develop this life-threatening condition.

Source: NIDDK (NIH)6

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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

Source: MedLinePlus (NIH)7

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It's important for diabetes to be diagnosed early so treatment can be started as soon as possible.

If you experience the symptoms of diabetes, visit your GP as soon as possible. They'll ask about your symptoms and may request blood and urine tests.

Your urine sample will be tested for glucose. Urine doesn't normally contain glucose, but glucose can pass from the kidneys into your urine if you have diabetes.

If your urine contains glucose, a specialised blood test known as glycated haemoglobin (HbA1c) can be used to determine whether you have diabetes.

Source: NHS Choices UK8

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Glycated haemoglobin (HbA1c) test

The glycated haemoglobin (HbA1c) test can be used to diagnose diabetes. It can also be used to show how well diabetes is being controlled.

The HbA1c test gives your average blood glucose level over the previous two to three months. The results can indicate whether the measures you're taking to control your diabetes are working, by meeting agreed personal targets.

If you've been diagnosed with diabetes, it's recommended that you have your HbA1c measured at least twice a year. However, you may need to have your HbA1c measured more frequently if:

  • you've recently been diagnosed with diabetes
  • your blood glucose remains too high
  • your treatment plan has been changed

The HbA1c test can be carried out at any time of day and doesn't require any special preparation, such as fasting. However, it's less reliable in certain situations, such as during pregnancy.

The advantages associated with the HbA1c test make it the preferred method of assessing how well blood glucose levels are being controlled in a person with diabetes.

HbA1c is also increasingly being used as a diagnostic test for type 2 diabetes, and as a screening test for people at high risk of diabetes.

Source: NHS Choices UK9

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Type 1 diabetes in children

The majority of children who develop diabetes will have type 1 diabetes.

You'll need to manage your child's condition as part of your daily life, but you'll be introduced to a specialist diabetes care team who can help you to come to terms with any challenges.

Read about diabetes and your child.

Source: NHS Choices UK10

Tests for Diabetes

What tests are used to diagnose diabetes and prediabetes?

Health care professionals most often use the fasting plasma glucose (FPG) test or the A1C test to diagnose diabetes. In some cases, they may use a random plasma glucose (RPG) test.

Fasting plasma glucose (FPG) test

The FPG blood test measures your blood glucose level at a single point in time. For the most reliable results, it is best to have this test in the morning, after you fast for at least 8 hours. Fasting means having nothing to eat or drink except sips of water.

A1C test

The A1C test is a blood test that provides your average levels of blood glucose over the past 3 months. Other names for the A1C test are hemoglobin A1C, HbA1C, glycated hemoglobin, and glycosylated hemoglobin test. You can eat and drink before this test. When it comes to using the A1C to diagnose diabetes, your doctor will consider factors such as your age and whether you have anemia or another problem with your blood.1 The A1C test is not accurate in people with anemia.

Your health care professional will report your A1C test result as a percentage, such as an A1C of 7 percent. The higher the percentage, the higher your average blood glucose levels.

People with diabetes also use information from the A1C test to help manage their diabetes.

Random plasma glucose (RPG) test

Sometimes health care professionals use the RPG test to diagnose diabetes when diabetes symptoms are present and they do not want to wait until you have fasted. You do not need to fast overnight for the RPG test. You may have this blood test at any time.

Source: NIDDK (NIH)11

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What test numbers tell me if I have diabetes or prediabetes?

Each test to detect diabetes and prediabetes uses a different measurement. Usually, the same test method needs to be repeated on a second day to diagnose diabetes. Your doctor may also use a second test method to confirm that you have diabetes.

The following table helps you understand what your test numbers mean if you are not pregnant.

Diagnosis -- A1C (percent) -- Fasting plasma glucose (FPG)[a] -- Oral glucose tolerance test (OGTT)[ab] Random plasma glucose test (RPG)[a]

Normal -- below 5.7 -- 99 or below -- 139 or below

Prediabetes-- 5.7 to 6.4 -- 100 to 125 -- 140 to 199

Diabetes -- 6.5 or above -- 126 or above -- 200 or above -- 200 or above

[a]Glucose values are in milligrams per deciliter, or mg/dL.

[b] At 2 hours after drinking 75 grams of glucose. To diagnose gestational diabetes, health care professionals give more glucose to drink and use different numbers as cutoffs.

Source: Adapted from American Diabetes Association. Classification and diagnosis of diabetes. Diabetes Care. 2016;39(1):S14-S20, tables 2.1, 2.3.

Source: NIDDK (NIH)12

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Which tests help my health care professional know what kind of diabetes I have?

Even though the tests described here can confirm that you have diabetes, they canít identify what type you have. Sometimes health care professionals are unsure if diabetes is type 1 or type 2. A rare type of diabetes that can occur in babies, called monogenic diabetes, can also be mistaken for type 1 diabetes. Treatment depends on the type of diabetes, so knowing which type you have is important.

To find out if your diabetes is type 1, your health care professional may look for certain autoantibodies. Autoantibodies are antibodies that mistakenly attack your healthy tissues and cells. The presence of one or more of several types of autoantibodies specific to diabetes is common in type 1 diabetes, but not in type 2 or monogenic diabetes. A health care professional will have to draw your blood for this test.

If you had diabetes while you were pregnant, you should get tested 6 to 12 weeks after your baby is born to see if you have type 2 diabetes.

Source: NIDDK (NIH)13

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Tests for Diabetes

Doctors use several blood tests to help diagnose diabetes:

  • Random plasma glucose testógiven at any time during the day
  • A1C testógiven at any time during the day; shows your glucose level for the past 3 months
  • Fasting plasma glucose testótaken after you have gone without food for at least 8 hours
  • Oral glucose tolerance testótaken after fasting overnight and then again 2 hours after having a sugary drink

Your doctor may want you to be tested for diabetes twice before making a diagnosis.

Source: NIA (NIH)14

Tests for Diabetes

A1C Test: A new fact sheet from NIH describes a blood test called A1C, which can diagnose type 2 diabetes and even prediabetes. Prediabetes raises your risk for developing type 2 diabetes.

You donít need to fast before taking the A1C test, so itís more convenient than other glucose tests often used to diagnose diabetes. The A1C test can also help patients with type 1 and type 2 diabetes to monitor their blood sugar (glucose) levels.

The new fact sheet covers a wide range of details about the A1C test, including how the test works, other blood tests for type 2 diabetes and prediabetes, the accuracy of blood tests and more.

The A1C Test and Diabetes fact sheet is available at www.diabetes.niddk.nih.gov/dm/pubs/A1CTest. Or contact NIHís National Diabetes Information Clearinghouse at 1-800-860-8747or email: ndic info.niddk.nih.gov.

Source: NIH News in Health (NIH)15

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Glucose tolerance test: Glucose tolerance tests are used when the results of the fasting blood glucose are borderline. They are also used to diagnose diabetes in pregnancy (gestational diabetes).

Source: Queensland Health16

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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

Source: MedLinePlus (NIH)17

Screening Tests for Diabetes

The preferred diagnostic screening test for type 2 diabetes is a blood sugar test called the fasting plasma glucose test, in which a blood sample is taken to assess blood sugar levels. In a fasting blood sugar test, a test result of 80 to 110 is considered normal, while results between 110 and 125 suggest a person is at risk of developing diabetes in the future. Levels higher than 125 indicate the presence of diabetes and the test must be repeated at a later date to confirm the diagnosis. Another test that measures blood sugar levels is the haemoglobin A1c (HbA1c) test. This test can indicate blood sugar levels over a period of time, while the typical blood sugar test measures blood sugar levels only at a specific point in time. The HbA1c test measures how much glucose in your blood stream has become bound to haemoglobin. Since blood cells last for about 90 days, the test can indicate how much glucose has been in the blood stream for the past one to three months. People who do not have diabetes should have HbA1c levels of about 3 percent to 6.5 percent. Anyone with diabetes should aim for HbA1c levels of about 8 percent.

Source: EC (EU)18

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Why should a person be tested for diabetes?

Testing is especially important because early in the disease diabetes has no symptoms. Although no test is perfect, the A1C and blood glucose tests are the best tools available to diagnose diabetesóa serious and lifelong disease.

Testing enables health care providers to find and treat diabetes before complications occur and to find and treat prediabetes, which can delay or prevent type 2 diabetes from developing.

Source: NIDDK (NIH)19

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Who should be tested for diabetes?

Anyone who has symptoms of diabetes should be tested for the disease. Some people will not have any symptoms but may have risk factors for diabetes and need to be tested. Testing allows health care professionals to find diabetes sooner and work with their patients to manage diabetes and prevent complications.

Testing also allows health care professionals to find prediabetes. Making lifestyle changes to lose a modest amount of weight if you are overweight may help you delay or prevent type 2 diabetes.

Blood tests help health care professionals diagnose diabetes and prediabetes.

Type 1 diabetes

Most often, testing for type 1 diabetes occurs in people with diabetes symptoms. Doctors usually diagnose type 1 diabetes in children and young adults. Because type 1 diabetes can run in families, a study called TrialNet offers free testing to family members of people with the disease, even if they donít have symptoms.

Type 2 diabetes

Experts recommend routine testing for type 2 diabetes if you

  • are age 45 or older
  • are between the ages of 19 and 44, are overweight or obese, and have one or more other diabetes risk factors
  • are a woman who had gestational diabetes1

Medicare covers the cost of diabetes tests for people with certain risk factors for diabetes. If you have Medicare, find out if you qualify for coverage . If you have different insurance, ask your insurance company if it covers diabetes tests.

Though type 2 diabetes most often develops in adults, children also can develop type 2 diabetes. Experts recommend testing children between the ages of 10 and 18 who are overweight or obese and have at least two other risk factors for developing diabetes.1

  • low birthweight
  • a mother who had diabetes while pregnant with them
  • any risk factor mentioned in Risk Factors for Type 2 Diabetes

Gestational diabetes

All pregnant women who do not have a prior diabetes diagnosis should be tested for gestational diabetes. If you are pregnant, you will take a glucose challenge test between 24 and 28 weeks of pregnancy.1

Source: NIDDK (NIH)20

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Do I need to be tested for diabetes?

Maybe. You should be tested for diabetes if you are between 40 and 70 years old and are overweight or obese. Your doctor may recommend testing earlier than age 40 if you also have other†risk factors for diabetes. Also, talk to your doctor about diabetes testing if you have†signs or symptoms†of diabetes. Your doctor will use a blood test to see if you have diabetes.

If the testing shows that your blood sugar levels are high, you can begin making healthy changes to your eating habits and getting more physical activity to help prevent diabetes.

Source: OWH (DHHS)21

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  1. Source: NIH News in Health (NIH): newsinhealth.nih.gov/ issue/ nov2014/ feature1
  2. Source: NICHD (NIH): nichd.nih.gov/ health/ topics/ diabetes/ conditioninfo/ pages/ diagnosed.aspx
  3. Source: EC (EU): ec.europa.eu/ health/ major_chronic_diseases/ diseases/ diabetes_en
  4. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ diabetes/ overview/ tests-diagnosis/ a1c-test
  5. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ diabetes/ overview/ tests-diagnosis
  6. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ diabetes/ overview/ managing-diabetes
  7. Source: MedLinePlus (NIH): medlineplus.gov/ a1c.html
  8. Source: NHS Choices UK: nhs.uk/ conditions/ type-1-diabetes/ diagnosis/ 
  9. ibid.
  10. ibid.
  11. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ diabetes/ overview/ tests-diagnosis
  12. ibid.
  13. ibid.
  14. Source: NIA (NIH): nia.nih.gov/ health/ diabetes-older-people
  15. Source: NIH News in Health (NIH): newsinhealth.nih.gov/ issue/ apr2012/ capsule2
  16. Source: Queensland Health: conditions.health.qld.gov.au/ HealthCondition/ condition/ 19/ 77/ 334/ glucose-tolerance-test
  17. Source: MedLinePlus (NIH): medlineplus.gov/ a1c.html
  18. Source: EC (EU): ec.europa.eu/ health/ major_chronic_diseases/ diseases/ diabetes_en
  19. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ diabetes/ overview/ tests-diagnosis/ a1c-test
  20. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ diabetes/ overview/ tests-diagnosis
  21. Source: OWH (DHHS): womenshealth.gov/ a-z-topics/ diabetes

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.