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Diabetes

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Tests

The goals of diabetes testing are to screen for high blood glucose levels (hyperglycemia), to detect and diagnose diabetes and prediabetes, to monitor and control glucose levels over time, and to detect and monitor complications.

Tests may be used:

  • When someone has signs and symptoms suggesting diabetes
  • When a person has risk factors or a condition that is associated with diabetes
  • When a person presents to the emergency room with an acute condition
  • On a regular basis, to monitor diabetes and glucose control

Screening for diabetes that occurs during pregnancy (gestational diabetes) is different than testing the general population. See the section on Gestational Diabetes for more on this.

According to the American Diabetes Association, a few different tests may be used for screening and diagnosis of diabetes or prediabetes and each test has advantages, disadvantages, and limitations. If the initial screening result from one of the tests listed below is abnormal, the test is repeated on another day. The repeat result must be abnormal to confirm a diagnosis of diabetes. Tests include:

  • Fasting glucose (fasting blood glucose, FBG) – this test measures the level of glucose in the blood after an 8-12 hour fast.
Fasting Glucose Level Indication
From 70 to 99 mg/dL (3.9 to 5.5 mmol/L) Normal fasting glucose
From 100 to 125 mg/dL (5.6 to 6.9 mmol/L) Prediabetes (impaired fasting glucose)
126 mg/dL (7.0 mmol/L) and above on more than one testing occasion Diabetes
  • A1c (also called hemoglobin A1c or glycohemoglobin) – this test evaluates the average amount of glucose in the blood over the last 2 to 3 months. For the A1c test, people don't have to fast for 8 hours or endure multiple blood samples being taken over several hours, but the test is not recommended for everyone. It should not be used for diabetes diagnosis in pregnant women, people who have had recent severe bleeding or blood transfusions, those with chronic kidney or liver disease, or people with blood disorders such as iron-deficiency anemia, vitamin B12 anemia, and hemoglobin variants. Also, only A1c tests that have been referenced to an accepted laboratory method (standardized) should be used for diagnostic or screening purposes. Currently, point-of-care tests, such as those that may be used at a doctor’s office or a patient’s bedside, are too variable for use in diagnosis but can be used to monitor treatment (lifestyle and drug therapies).
A1c Level Indication
Less than 5.7% (39 mmol/mol) Normal
5.7% to 6.4% (39-46 mmol/mol) Prediabetes
6.5% (47 mmol/mol) or higher Diabetes
  • 2-hour glucose tolerance test (OGTT) – this test involves drawing a fasting blood test, followed by having a person drink a 75-gram glucose drink and then drawing another sample two hours after consuming the glucose.
Glucose Level 2 Hours After 75-gram Drink Indication
Less than 140 mg/dL (7.8 mmol/L) Normal glucose tolerance
From 140 to 199 mg/dL (7.8 to 11.1 mmol/L) Prediabetes (impaired glucose tolerance)
Equal to or greater than 200 mg/dL (11.1 mmol/L) on more than one testing occasion Diabetes
  • Sometimes a blood sample may be drawn and glucose measured when a person has not been fasting, for example, as part of a comprehensive metabolic panel (CMP). A result of 200 mg/dL (11.1 mmol/L) or higher indicates diabetes. An abnormal result may be followed up with additional testing.

For screening only:

  • Sometimes urine samples are tested for glucose, protein, and ketones, often as part of a urinalysis, during a routine physical examination. If glucose and/or protein or ketones are present in the urine sample, the person has a problem that needs to be addressed. Additional testing is usually done to identify the cause of the abnormal urine result.

Tests for monitoring:

  • Glucose – type 1 diabetics must monitor their own blood glucose levels, often several times a day, to determine how far above or below normal their glucose is and, based on their healthcare provider's instructions, what modifications they should make to their medications. This is usually done by placing a drop of blood (obtained by pricking the skin with a small lancet device), onto a glucose strip and then inserting the strip into a glucose meter, a small machine that provides a digital readout of the blood glucose level. Some type 2 diabetics and pregnant women diagnosed with gestational diabetes may also need to monitor their blood glucose in this way.
  • A1c and estimated average glucose (eAG) – this is a test and a calculation that are ordered several times a year to monitor diabetics and sometimes people with prediabetes. A1c is a measure of the average amount of glucose present in the blood over the last 2 to 3 months and helps a health practitioner to determine how well a treatment plan is working to control someone's blood glucose levels over time.

Several other laboratory tests may be used to evaluate glucose control, organ function, and to detect emerging complications. These may include:

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