Understanding the GTT Test at Home: Preparation, Process, and Results
Time to read 13 min
Time to read 13 min
Table of contents
A glucose tolerance test helps to determine diabetes and other ailments related to high blood sugar. A GTT is performed to confirm whether your body can store and utilise glucose, and the glucose tolerance test results provide insight into this process. This test is most commonly used to diagnose diabetes. However, the other diabetes diagnostic tests, such as an A1C test and other uses of a GTT, are also effective.
A glucose tolerance test can be suggested by your healthcare provider to confirm the presence of the following conditions, including risk factors for diabetes:
Diabetes (normally prediabetes, Type 2 diabetes or gestational diabetes).
Insulin resistance.
Reactive hypoglycemia (lowered blood sugar level).
Acromegaly.
Unusual carbohydrate metabolic disorders.
It is also worth mentioning that these conditions could be diagnosed with the help of other tests. Your provider can prescribe a combination of more than one diagnostic test.
A glucose challenge test is a regular screening test that is performed on a pregnant woman to determine gestational diabetes and assess the response to the oral glucose load. In case the findings are abnormal, your provider may prescribe an oral glucose tolerance test alongside a three-hour OGTT to confirm or eliminate the condition officially.
The Glucose Tolerance Test (GTT) checks the efficiency of your body to process glucose. It is usually employed in the diagnosis of diabetes, prediabetes, pregnancy, and gestational diabetes using a glucose solution. The test procedures are the following;
The GTT test involves a rigorous fasting phase of 8-10 hours, where you should avoid any foods, caloric beverages. The only item you can take is plain water. During this period, smoking, caffeine intake and intense physical activity should be avoided because they would change the level of glucose.
Once you get to the lab or when you are ready to take the GTT test, the technician will take your fasting blood glucose sample. This reading will give you an idea of your glucose level.
Once the baseline sample is performed, you will be requested to consume a glucose solution with a fixed quantity of sugar in it. Usually, 75g of normal glucose is recommended, and 100g is recommended for pregnant women. India and WHO commonly use a 75-g, 2-hour OGTT for pregnancy. The beverage has to be drunk in a duration of approximately five minutes. This glucose charge provokes an increase in blood sugar, which allows clinicians to observe the efficiency of your body in its effect.
The blood samples are taken at defined intervals after taking the glucose drink to check how your body responds to glucose and assess your glucose tolerance. In most cases, the common collection times are 1 hour, 2 hours and occasionally 3 hours after the consumption of the solution. You can’t consume anything except a small amount of water. Also, don't perform any physical activity, as this will disrupt the outcome.
Time spent in the test differs depending on the protocol. On average, a normal GTT takes approximately 2 hours, whereas the pregnancy-specific OGTT (which in some instances carries an extra 3-hour reading) may take 3-4 hours. The test has intervals between blood pulls.
You should have a normal diet in the days before the test and avoid eating or drinking anything except water. Avoid alcohol for at least 24 hours before the test. Notify the healthcare provider in case you are sick, stressed, or taking medications which can affect glucose levels as part of your medical care.
When pregnant women are administered the GTT test procedure, they are likely to feel nauseated by the glucose drink, and they must prepare to sleep during and after taking the test.
The GTT test can be performed in the comfort of the home. Many labs provide the home collection service. MyDiagnostics is one of the best labs that provides accurate reports. They send a certified phlebotomist to your doorstep to collect blood samples to test the blood glucose level.
The glucose drink is brought by providers. This is the most convenient choice for people who do not want to go out of the house while fasting or those who want to experience the testing more comfortably.
Time Point |
Event |
Purpose |
0 Hour (Fasting) |
Baseline blood sample |
Measures fasting glucose |
Glucose Drink |
Consume 75g/100g glucose |
Creates a glucose load |
1 Hour |
First post-glucose sample |
Measures initial glucose spike |
2 Hours |
Second sample |
Checks glucose clearance |
3 Hours (if applicable) |
Third sample (mainly for pregnancy OGTT) |
Evaluates late glucose processing |
The Glucose Tolerance Test (GTT) measures how effectively your body handles a glucose load over time, and thus, the glucose tolerance test measures your metabolic response. Glucose levels, including plasma glucose, are checked at fasting, 1 hour, and 2 hours (and sometimes 3 hours in pregnancy).
The Glucose Tolerance Test (GTT) measures the glucose processing of the body following a standardized increase in sugar load. During the fasting stage (0 hours), a normal blood glucose level is under 100mg/dL. Measurements between 100-125mg/dL are impaired fasting glucose, and above 126mg/dL is a diabetic range.
An ordinary response is below 180 mg/dL one hour after intake of the glucose drink. These test results indicate that anything between 180-199 mg/dL is an impairment, and 200 mg/dL and above is diabetes. These levels are recommended in non-pregnant adults. The instance of 2-hour reading is the most sensitive: anything under 140mg/dL is normal, 140-199 mg/dL indicates abnormal glucose tolerance, and 200mg/dL and above is diabetes.
Normal: < 100 mg/dL
Abnormal fasting glucose: 100-125mg/dl.
Diabetic range: ≥ 126 mg/dL
Normal: < 180 mg/dL
Impaired: 180–199 mg/dL
Diabetic range: ≥ 200 mg/dL
Normal: < 140 mg/dL
Impaired Glucose Tolerance (IGT): 140-199mg/dl.
Diabetic range: ≥ 200 mg/dL
Normal GTT outcomes include the clearance capacity of glucose in the bloodstream. All the values remain within the normal range at the levels of fasting, 1 hour and 2 hours. Once glucose levels exceed the normal range, the condition is known as impaired glucose tolerance or prediabetes.
It is a lack of sensitivity to insulin and a high probability of developing diabetes in the future. The values that hit or exceed the diabetic cutoffs during any of the time points are indicative that the body fails to successfully handle glucose. Consequently, it leads to diabetes, and should be followed by additional medical testing and treatment.
The gold standard of diagnosing glucose metabolism disorders is enjoyed by the blood GTT. Normal GTT blood samples indicate that fasting glucose is lower than 100mg/dL, the 1-hour peak is less than 180mg/dL, and the 2-hour is less than 140mg/dL.
These values indicate normal insulin studies and normal glucose consumption. Any level that exceeds these levels assists clinicians in gaining knowledge on impaired glucose tolerance or diabetes, depending on the test results obtained.
The urine GTT is no longer in widespread use. However, it can be done as a supplementary test. In a healthy state, glucose is not supposed to be found in the urine at any time since, under normal conditions as the kidneys can reabsorb the glucose effectively.
The presence of glucose in the urine, or glycosuria, could be an indication of elevated blood glucose levels or low renal threshold, which requires diabetes care. The abnormal GTT result in the urine should always be compared with the blood tests and blood sugar level to come up with a precise diagnosis.
GTT Interpretation Table
Time After Glucose Intake |
Normal (mg/dL) |
Impaired (mg/dL) |
Diabetic (mg/dL) |
Fasting |
< 100 |
100–125 |
≥ 126 |
1 hour |
< 180 |
180–199 |
≥ 200 |
2 hour |
< 140 |
140–199 |
≥ 200 |
In normal physiological conditions kidneys reabsorb almost all the filtered glucose. For a typical urine GTT:
Normal urine glucose: No or < 15 mg/dl.
The traces can sometimes be present, but they are to be small and temporary.
Unstable or substantial persistence of glucose at either fasting or following glucose intake indicates that there is glycosuria.
In a healthy body, the glucose levels in the urine should not contain any glucose. The presence of glucose in the urine during the test normally shows that the blood sugar levels have exceeded the kidneys.
The urine glucose tolerance test (urine GTT) is not used widely compared to the blood GTT. It is a secondary test and not a diagnostic aid. Although the GTT in the blood measures the specific amount of glucose present in the blood, at fasting levels and during the timed levels. The urine GTT measures the presence of glucose that has overflowed into the urine after the patient has ingested glucose.
Since kidneys usually stop glucose from entering the urine, the urine GTT is less accurate and may be affected by the changes in the kidneys instead of the blood glucose itself. Hence, the urine GTT is not applied to the diagnosis of diabetes; however, it can be used to suggest glycosuria (glucose in urine) when the excretion is combined with the blood glucose levels.
High GTT outcomes may be caused by several reasons, and may require further tests for accurate diagnosis to achieve a normal result.
Insulin resistance, a disease state in which our body cells become less sensitive to insulin, and thus glucose remains high in the blood.
Gestational diabetes mellitus (GDM) is a condition, which the body fails to maintain normal levels of blood glucose following meals.
Stress, acute illness or some medicines, acute stress, infection or some drugs (such as steroids) may temporarily elevate blood sugar levels and give GTT results.
Lifestyle factors, malnutrition (rich in refined carbs/sugars), lack of physical exercise or obesity can predispose to abnormal GTT reactions.
A high (abnormal) GTT does not necessarily imply the presence of diabetes. Sometimes it is the beginning of glucose intolerance (prediabetes) or a temporary malfunction (stress, illness). However, by detecting glucose intolerance early, you can control it before it brings severe complications. Early lifestyle modifications or therapy can significantly decrease the health risks in the long run.
Prevalence of Prediabetes and Gestational Diabetes in India (2024-2025) is a study that focuses on population trends in this specific area.
Recent statistics on a national survey indicate that approximately 15.3% of Indians are estimated to have prediabetes or dysglycemia.
One more research estimates that approximately 11.4 per cent of India's grown-ups have diabetes.
In terms of pregnancy glucose intolerance, a meta-analysis has estimated the prevalence of gestational diabetes (or GDM) in India to be about 13% (95% CI: 9-16 % ) in expectant mothers.
A standard Glucose Tolerance Test (GTT) in most cities of India costs approximately ₹ 300 to ₹ 800. Other more inclusive GTT packages cost somewhat ₹ 800 to ₹1000+, depending on the laboratory and sample count. Price can be higher in the case of pregnancy-related GTTs. It depends upon which lab and services you choose.
Why does the cost vary?
The price is determined by some factors like city (metro vs smaller city), type of lab (government, small lab, large chain), quantity of blood-draw samples, and other types of services (such as processing, reporting, doctor consultation) offered.
The Fasting Blood Sugar (FBS) test is used to check the level of glucose in your blood after an overnight fast. It is a fast and easy screening device that can identify high levels of fasting blood sugar.
Conversely, the Glucose Tolerance Test (GTT) evaluates your body's response to a glucose load over time. The GTT looks at how your body handles sugar by testing the blood glucose at different intervals.
The FBS test measures the blood glucose only under the fasting condition, providing a picture of the glucose level at baseline.
The GTT measures the blood glucose at fasting and at defined intervals following intake of a glucose drink. The usual intervals are usually 1 hour, 2 hours and occasionally 3 hours. This helps in detecting abnormalities that can’t be observed with fasting glucose.
FBS is capable of detecting high fasting glucose and can be applied in the routine screening of diabetes.
GTT, on the other hand, is more sensitive when it comes to identifying early glucose intolerance, insulin resistance and gestational diabetes.
The FBS test is fast; only one blood sample is required with 8-10 hours of fasting.
The GTT is extended and requires 2-3 hours and includes the fasting process, intake of glucose solution, and several timed blood samples.
The Glucose Tolerance Test (GTT) are pretty useful in measuring the glucose metabolism of the body. It offers a quick evaluation of the fasting glucose and is more extensive in the evaluation of the overall way the body processes sugar over time. Hence, it is necessary in the detection of prediabetes, early insulin resistance, and gestational diabetes.
Below 100mg/dL is considered normal in a fasting GTT test. A level below 140mg/dL is considered normal after 2 hours of consuming glucose. A reading of 140-199mg/dL would be prediabetes, and 200mg/dL or more would be diabetes.
Yes, one can perform a GTT test at home with the help of the home sample collection service offered by a certified lab. A phlebotomist comes and takes fasting and post-glucose blood samples and forwards them to the lab. Nevertheless, the test cannot be self-administered.
GTT ranges vary during pregnancy, particularly during the 24 to 28 weeks screening period. Fasting glucose must be less than 92mg/dL. One-hour reading must not exceed 180mg/dL, and the 2-hour reading must not exceed 153mg/dL. In case one or more of the values exceed the limit, it could signify gestational diabetes that needs additional evaluation and care.
The GTT urine test is an approach that involves the collection of the urine samples at predetermined time points following the intake of the solution containing glucose. To start with, urine is inspected by means of fasting. The patient then takes the glucose drink, and samples of urine are taken every 30 to 60 minutes up to 2-3 hours. The lab checks the quantity of glucose excretion to determine kidney processing of glucose and sugar tolerance.
Having high GTT values, that is, glucose tolerance is impaired, prediabetes, diabetes, or gestational diabetes (in pregnancy). High values imply that your body is not utilizing glucose. The doctor can recommend lifestyle changes, nutrition, medications or further tests to assess the condition for better disease control. Early intervention assists in avoiding prolonged complications of the heart, nerve damage or kidney problems associated with growth hormone.
GTT could be suggested every 1-3 years to patients with a high risk of diabetes. It is normally experienced by pregnant women at a time between 24- 28 weeks. In known prediabetics, the test can be done more often with regard to the symptoms, weight gain, or the recommendation of the doctor.
In the case of a GTT test, one should fast for 8-10 hours before the test, just taking water. Normal meals should be taken in the three days before testing to ensure the accuracy of your fasting blood sugar level. Do not smoke, take alcohol, or indulge in heavy exercise for 24 hours.
Yes, GTT is different. A fasting glucose test measures the glucose concentration in your system following a period of fasting. HbA1c attests to average blood sugar levels in 3 months. The GTT measures the performance of your body in terms of sugar over time by assessing fasting and post-glucose levels. GTT identifies early abnormalities that are not all-inclusive in the fasting sugar or HbA1c.
**Medical Disclaimer: The following information is for educational purposes only. No information provided on this website, including text, graphics, and images, is intended as a substitute for professional medical advice. Please consult with your doctor about specific medical advice about your condition(s).
