Glucose Tolerance Test (GTT, 100 Grams)
The 100g GTT is a diagnostic test for gestational diabetes. After an overnight fast, blood sugar is measured fasting and at 1, 2, and 3 hours after drinking 100 grams of glucose solution.
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What the Glucose Tolerance Test (GTT, 100 Grams) test tells you
This is the longer, confirmatory step in the classic two-stage pathway for gestational diabetes. If the shorter, non-fasting glucose challenge screen came back above the laboratory's screening level, this is the test that settles whether gestational diabetes is actually present. It is a timed procedure rather than a single blood draw, and it takes most of a morning, so it helps to plan the appointment with that in mind.
The sequence is fixed. You arrive having fasted overnight and a first blood sample is taken before anything is drunk, establishing your starting point. You then drink the measured 100-gram glucose solution, and further samples are taken at set intervals over the following three hours — at one hour, at two hours and at three hours. You stay at the facility throughout, without eating, drinking anything but the water you are permitted, smoking or walking about, because all of those change how quickly glucose leaves the blood and would make the readings impossible to compare.
What this pattern of samples reveals is something a single measurement cannot: not just where your blood sugar starts, but how high it climbs after a large load and how promptly it comes back down. That curve is what distinguishes a pancreas comfortably keeping pace with the insulin resistance of pregnancy from one that is not. Importantly, the diagnosis rests on more than one of the timed readings sitting above the laboratory's limits, rather than on any single value, which is one reason the whole sequence has to be completed. Where gestational diabetes is confirmed, it is treated with diet, blood sugar monitoring and sometimes medication, and that treatment substantially reduces the risks to both mother and baby — which is the entire reason the pathway exists.
Performed after a positive GCT screening to confirm or rule out gestational diabetes.
The screening test only raises a question. This is the test that answers it, so that treatment is started only where it is genuinely needed.
Timed samples show how high blood sugar climbs and how quickly it returns, which a single measurement cannot reveal.
Identifying gestational diabetes allows diet, monitoring and treatment to begin in time to lower the risks for mother and baby.
Many women who screen positive do not have gestational diabetes, and this test is what spares them a treatment plan they do not need.
Reasons your doctor may request the Glucose Tolerance Test (GTT, 100 Grams) test
Your doctor may order this test for any of the reasons below. Some are routine checks, others follow specific symptoms or an earlier result.
Confirming gestational diabetes
A glucose challenge screening result above the laboratory's screening level during pregnancy.
Strong clinical suspicion of gestational diabetes even where screening was borderline.
A previous pregnancy
Gestational diabetes in a previous pregnancy, where a confirmatory test is planned directly.
A previous unusually large baby or other features that raise concern about glucose handling in pregnancy.
Sugar found in the urine
Sugar repeatedly found in the urine during antenatal checks.
Pick a morning slot online or on WhatsApp — come fasted per the prep note below.
A DHA-licensed nurse collects your sample at home or in the office — free home collection.
A physician-reviewed, easy-to-read report lands securely by WhatsApp and email.
A timed test of blood sugar after a 100g glucose load.
Glucose Tolerance Test (GTT, 100 Grams)
A timed test of blood sugar after a 100g glucose load.
Blood sugar is measured at several time points (fasting and after the glucose drink). Each value is interpreted against its own target. See your detailed report.
This test is reported descriptively rather than on a numeric scale — each finding below explains what your report may say.
This information is for general education only and is not medical advice. Reference ranges can vary by laboratory, age, sex, and individual factors. Always consult your physician or doctor to interpret your results.
What a higher result can point to
- Gestational diabetes, in which the pancreas cannot fully overcome the insulin resistance created by pregnancy hormones.
- Type 2 diabetes that was present before the pregnancy but had not been diagnosed.
- Steroid treatment given during pregnancy, which raises blood sugar while it is being taken.
- Restricting carbohydrate in the days before the test, which paradoxically worsens the body's handling of the glucose load.
What a lower result can point to
- An exaggerated or delayed insulin response, which drives the level down in the later hours of the test.
- Previous stomach or weight-loss surgery, which speeds absorption of the sugar load and then its clearance.
- Glucose-lowering medicine taken before the test rather than after it.
These are possibilities, not diagnoses. A single value outside the reference range is interpreted alongside your symptoms, history and other tests — your doctor decides what it means for you.
What this test cannot tell you
- The test only works if the whole sequence is completed; leaving early, eating or being sick partway through means it usually has to be repeated on another day.
- It is demanding, requiring an overnight fast and several hours at the facility with repeated blood samples, which some women find difficult.
- It describes glucose handling at one point in pregnancy, so a result within the expected range does not guarantee blood sugar will remain so as the pregnancy advances.
- Illness, steroid treatment and carbohydrate restriction beforehand can all shift the readings, so context matters when your doctor interprets them.
Risks of the blood draw
- Mild bruising or brief soreness where the needle went in.
- Occasional lightheadedness, which settles after a few minutes of rest.
- Bleeding or infection at the site, which is rare with sterile single-use equipment.
- 1Fasting overnight is required; only plain water should be taken before the first sample.
- 2Several blood samples are taken at set intervals over three hours and you must stay at the facility throughout.
- 3Eat your normal diet, including your usual carbohydrate, in the days beforehand.
- 4The diagnosis depends on the pattern across the timed samples, not on any single reading.
- 5A confirmed diagnosis is manageable, and treatment is what protects both mother and baby.
Frequently Asked Questions
Everything you need to know about the Glucose Tolerance Test (GTT, 100 Grams) test. Can't find what you're looking for?
Talk to our team→Because the useful information is in the shape of the response. Timed samples show how high blood sugar rises after the drink and how promptly it falls again. A single value cannot distinguish a pancreas that is keeping pace from one that is struggling.
Food adds more glucose, smoking and activity change how fast muscles take glucose out of the blood, and either would make your readings incomparable with the standard the test is judged against. Sitting quietly is part of the procedure, not just convenience.
No. Restricting carbohydrate in the days beforehand actually makes the body less efficient at handling the glucose load, which can push the readings higher. Eating your normal diet is the way to get an accurate result.
Your doctor will discuss a plan, which usually starts with dietary changes and home blood sugar monitoring, with medication added if needed. Most pregnancies affected by gestational diabetes proceed well once blood sugar is managed, and the condition commonly resolves after delivery.
The 100g GTT is a diagnostic test for gestational diabetes. After an overnight fast, blood sugar is measured fasting and at 1, 2, and 3 hours after drinking 100 grams of glucose solution.
Performed after a positive GCT screening to confirm or rule out gestational diabetes.
Yes. We recommend fasting for 10-12 hours before your Oral Glucose Tolerance (100g) test; plain water is fine. Overnight fasting (8–14 hours) is required. A high-carbohydrate diet for 3 days before the test is recommended.
The Oral Glucose Tolerance (100g) test uses a plasma (naf) sample, collected quickly by our DHA-licensed phlebotomist with minimal discomfort.
Results for the Oral Glucose Tolerance (100g) test are typically ready within 1 day. You will receive a secure digital report, and your Smart Report highlights anything outside the normal range.
The Oral Glucose Tolerance (100g) test is AED 120, which includes free home sample collection and a physician-reviewed report. You can also build a custom panel and pay only for the markers you choose.
Yes. A DHA-licensed phlebotomist can collect your sample at home or the office anywhere in Dubai at no extra cost, 7 days a week. See how it works.
It is commonly chosen by adults at metabolic risk. If you are not sure it is right for you, our care team is happy to advise.
Add the Oral Glucose Tolerance (100g) test to your cart and complete the short booking wizard, choosing home collection or a lab visit. Guest checkout lets you book without creating an account.
Yes. It is processed at our EIAC-accredited laboratory (ISO 15189:2022) under DHA license 0046381 and verified by board-certified pathologists.
Every report includes reference ranges and plain-language notes. If you have questions, our care team can arrange a clinician review — just get in touch.
Absolutely. Add it to a curated health package or bundle it with any of our 160+ biomarkers, often from a single sample in one visit.