Oral glucose tolerance test (OGTT)
Measures how well your body clears a set dose of sugar over two hours - a sensitive test for prediabetes and diabetes.
TypeBlood test
HowFasting blood test, then a sugary drink, then more blood tests over 2 hours.
How oftenWhen other results are unclear, or in pregnancy.
BeforeFast 8–12 hours; eat normally in the days before. Stay seated during the test.
WhoPeople with borderline HbA1c or glucose, or in pregnancy screening.
Watching your body handle sugar in real time
Fasting glucose and HbA1c show averages. A glucose tolerance test gives you a sugary drink and measures how quickly your body clears it - catching problems the averages can miss.
Fasting glucose
“What’s my baseline?”
One reading before eating.
Snapshot
HbA1c
“What’s my 3-month average?”
Convenient, but affected by anemia and some conditions.
Average
Glucose tolerance
“How do I handle a sugar load?”
Shows the response - standard in pregnancy and when other tests disagree.
Response
Is it right for you?
Worth considering if…
- Your HbA1c and glucose disagree or are borderline.
- You’re pregnant (gestational diabetes screening).
- Your provider suspects early diabetes that other tests missed.
A better option if…
- You want a quick first check - HbA1c or fasting glucose is simpler.
- You want everyday patterns - a CGM shows those.
How it’s measured
Standard 2-hour OGTT
75 g glucose drink; blood at 0 and 2 hours.
With insulin
Some labs add insulin levels to show how hard your pancreas works.
Pregnancy versions
Different doses and timings are used in pregnancy.
The full picture
What is it?
A test that measures blood sugar before and after drinking a set amount of glucose.
What type of test is it?
A blood test.
What does it measure?
How high your glucose rises and how fast it comes back down.
Why might someone consider it?
It can pick up problems that fasting glucose and HbA1c miss.
Who is it most relevant for?
People with borderline results and pregnant people.
How is it performed?
Fasting blood draw, a sweet drink, then another draw after 2 hours.
How often might it be considered?
Only when needed.
What can the result help you understand?
Whether your body handles sugar normally.
What are its limitations?
It takes 2+ hours, results can vary day to day, and it can cause nausea.
What should it be viewed with?
HbA1c, fasting glucose, fasting insulin, weight and family history.
Where to get it
Through your provider
Usually ordered when symptoms or results point to it.
Lab services
e.g. Quest Diagnostics, Labcorp - typically with a provider order.
Specialists
Your provider may refer you to a specialist to interpret it.
Names are examples only, not endorsements. Your provider can often order the same test - and help interpret it.
Connected to
Questions to ask your provider
- Do I need an OGTT or is HbA1c enough?
- Should insulin be measured too?
Ziva Health
One test is a snapshot. Ziva shows the whole story.
Ziva brings your lab results, wearables and daily readings together - and Isabella tells you what’s changing and what to ask your provider next.
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Being listed doesn’t mean everyone needs this test. Educational only — not medical advice. Results should be interpreted with a qualified clinician. ← Back to Know What to Test