Glucose Tolerance Test & Blood Glucose Testing
Diabetes screening tests provide doctors with a strong indication of whether you have diabetes.
There are a number of different screening tests which may be chosen to diagnose diabetes depending on which type of diabetes is suspected.
In most cases you will have two tests on separate days to confirm diabetes. However, a repeat test may not be needed if the result is very high.
Random plasma glucose test
A random plasma glucose test can be carried out simply and will often be used in the diagnosis of type 1 diabetes.
If the doctor is testing for type 1 diabetes, a test for ketones in the blood or urine may also be performed.
A random plasma glucose test involves taking a sample of blood at any time of day and measuring the concentration of glucose in the sample.
A reading of 200 mg/dL or more for a random blood or urine test will confirm a diagnosis of diabetes.
Oral glucose tolerance test
An oral glucose tolerance test (OGTT) can be used to diagnose type 1 diabetes, type 2 diabetes, prediabetes and gestational diabetes.
This test involves taking a drink containing 75g of glucose and having blood glucose levels monitored before having the drink of glucose and 2 hours afterwards.
|Time of test||Normal||Impaired glucose tolerance (IGT)||Diabetes|
|2 hours after start of test||Under 140 mg/dL||140 to 199 mg/dL||200 mg/dL or over|
An A1c test is largely used to measure long-term diabetes control but can also show whether people with prediabetes are progressing towards having type 2 diabetes.
An A1c test measures the level of glycated hemoglobin in the blood, which gives a good indication of how high your blood glucose levels have been on average over the past 2 to 3 months.
The test involves having a sample of blood taken, usually from your arm, which is then analyzed to give the A1c result.
The American Diabetes Association advises the following A1c boundaries to determine diabetes and glucose intolerance:
|Normal||Impaired glucose regulation (IGR)||Diabetes|
|Under 5.7%||5.7 to 6.4%||6.5% or above|
Fasting plasma glucose (FPG) test
Fasting plasma glucose tests are commonly used to test for type 2 diabetes or Impaired Fasting Glucose (IFG), a form of prediabetes.
A fasting plasma glucose test involves taking a blood sample, usually from your arm, which is then tested for the glucose level.
You will need to fast, by not having anything to eat or drink except water, for at least 8 hours before the test.
|Normal||Impaired fasting glucose (IFG)||Diabetes|
|Under 100 mg/dL||100 to 125 mg/dL||126 mg/dL or over|
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Last reviewed: January 21, 2015 at 10:39
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