What is a Glucose tolerance test?
A lab test called the glucose tolerance test measures how quickly your body transports sugar from the blood to tissues like muscle and fat. The exam is frequently used to identify diabetes.
The tests used to screen for diabetes during pregnancy are same, but they are performed differently.
Why is the test done?
The sugar that the body utilizes as fuel is called glucose. Untreated diabetic patients have elevated blood glucose levels.
The following first tests are frequently used to identify diabetes in adults who are not pregnant:
- If the fasting blood glucose level is more than 126 mg/dL (7 mmol/L) on two independent tests, diabetes is diagnosed.
- Diabetes is identified if the hemoglobin A1c test result is 6.5% or above.
Diabetes can also be identified via glucose tolerance testing. When a person's fasting blood glucose level is high but not high enough (over 125 mg/dL or 7 mmol/L) to fulfill the diagnosis for diabetes, the OGTT is used to screen for or diagnose diabetes.
An early indication of diabetes than an abnormal fasting glucose is aberrant glucose tolerance, which occurs when blood sugar levels rise excessively following a glucose challenge.
How the test is administered
The oral glucose tolerance test is the most used type of glucose tolerance evaluation (OGTT).
Blood will be sampled before the test starts.
The next step will need you to consume a liquid containing a specific level of glucose (usually 75 grams). After the solution, your blood will be drawn again every 30 to 60 minutes.
The exam might last up to three hours.
The intravenous (IV) glucose tolerance test is a comparable examination (IGTT). Diabetes is seldom and hardly ever diagnosed using this method. In one variation of the IGTT, you receive a 3-minute glucose injection into a vein.
How to prepare for the exam
Following are the points to remember before the test:
- Make sure you eat normally for some days before the test.
- At least eight hours before the test, refrain from eating or drinking anything. You cannot eat while taking the exam.
- If any of the medications you take have the potential to alter the outcome of the test, ask your doctor.
The Experience of the Test
The glucose solution is equivalent to a highly sweet drink when consumed.
It is extremely rare for this test to have serious negative effects. After consuming the glucose, some patients experience nausea, dizziness, lightheadedness, or even fainting symptoms during the blood test. If you have a history of these symptoms following blood tests or other medical procedures, let your healthcare professional know.
Is there any risk associated with the test?
No, there is no risk or danger of having a blood test. One might feel bruising or discomfort when the needle goes inside but it will disappear soon.
Understanding the results
Normal blood values for a 75-gram OGTT used to check for type 2 diabetes in those who are not pregnant:
Fasting - 60 to 100 mg/dL (3.3 to 5.5 mmol/L)
1 hour - Less than 200 mg/dL (11.1 mmol/L)
2 hours - This value is used to make the diagnosis of diabetes.
- Less than 140 mg/dL (7.8 mmol/L) is normal.
- Between 141 mg/dL and 200 mg/dL (7.8 to 11.1 mmol/L) is considered impaired glucose tolerance.
- Above 200 mg/dl (11.1mmol/L) is diagnostic of diabetes.
The mentioned levels serve as standard benchmarks for these tests' outcomes. Different laboratories may have somewhat different normal value ranges. Several laboratories test various samples or use various metrics. Ask your physician what your particular test findings signify.
In pregnancy normal results
- GTT Fasting: ≥92 mg/dL (5.1 mmol/L),
- One hour: ≥180 mg/dL (10 mmol/L),
- Two hour: ≥153 mg/dL (8.5 mmol/L)
If your blood glucose level is greater than usual, you may have diabetes or pre-diabetes:
- Impaired glucose tolerance refers to a 2-hour result between 140 and 200 mg/dL (7.8 and 11.1 mmol/L). You are now more likely to eventually get diabetes or you are pre-diabetic.
- Diagnosing diabetes requires a blood glucose level of 200 mg/dL (11.1 mmol/L) or greater.
Your blood glucose level may increase if your body experiences significant stress, such as that brought on by trauma, stroke, heart attack, or surgery. Your blood glucose level can be lowered by vigorous exercise.
Your blood sugar level can be increased or decreased by several medications. Inform your physician of any medications you are taking before the test.