Glucose tolerance test: what’s a normal result?
Below 7.8 at two hours is normal, pregnant or not. But you get two results. The one taken before the drink can flag a problem by itself, and in pregnancy its line is 5.6.
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What are normal glucose tolerance test results?
Two hours after the sugar drink, below 7.8 mmol/L is normal. An NHS lab calls it non-diabetic, using World Health Organization lines.
Think of the test as a timed clear-up. Everyone gets the same dose of sugar.
The 2-hour number shows how much is still in your blood. The more still there, the more trouble your body is having handling sugar.
- Below 7.8 mmol/LNon-diabetic.
- 7.8 to just under 11.1 mmol/LImpaired glucose tolerance.
- 11.1 mmol/L or aboveDiabetes range.
Source: NHS pathology (WHO criteria)
From 7.8 up to 11.1 is impaired glucose tolerance. Your body is having problems handling sugar, but you’re not in the diabetes range. At 11.1 or more, you are.
No symptoms? One result in the diabetes range isn’t enough. The lab needs a second one on another day.
In the middle band? Ask your care team how eating better and exercise can help prevent type 2 diabetes. More in our prediabetes guide.
Why does the fasting result matter?
The test takes two blood samples. One is before the drink, after a night without food. That’s your fasting result.
It has its own lines, so it can flag a problem even when your 2-hour number is fine. Fasting 6.1 to 6.9 is impaired fasting glucose: higher than it should be, but not in the diabetes range.
| Result | Not pregnant | Pregnant |
|---|---|---|
| Fasting, before the drink | 6.1 to 6.9: impaired fasting glucose. 7 or more: diabetes range. | 5.6 or above: gestational diabetes. |
| 2 hours after the drink | Below 7.8: non-diabetic. 7.8 up to 11.1: impaired glucose tolerance. 11.1 or more: diabetes range. | 7.8 or above: gestational diabetes. |
Sources: NHS pathology; Diabetes UK; NICE NG3
Gestational diabetes is high blood sugar that starts in pregnancy.
Pregnant? NICE needs only one of the two: fasting 5.6 or above, or 2-hour 7.8 or above. So a fasting 5.7 with a 2-hour 6.5 still counts as gestational diabetes.
Diagnosed? NICE says you should be offered a review at a joint diabetes and pregnancy clinic within 1 week.
Who needs a glucose tolerance test?
Outside pregnancy, most people don’t. A fasting or random sugar test, or an HbA1c, can usually settle it. HbA1c is a blood test of your average sugar over the last 2 to 3 months.
A lab may use a GTT after a fasting result of 6.1 to 6.9. See our fasting glucose guide.
In pregnancy, you should be offered one at 24 to 28 weeks if you have one or more of these:
- you’re over 40
- your BMI is above 30
- you had a baby who weighed 4.5kg (10lb) or more at birth
- you had gestational diabetes before
- a parent, brother or sister has diabetes
- you’re of south Asian, Black, African-Caribbean or Middle Eastern origin, even if you were born in the UK
- you’ve had a gastric bypass or other weight-loss surgery
Had gestational diabetes before? You’ll be offered a test soon after your booking appointment. If it’s normal, you get another at 24 to 28 weeks.
Gestational diabetes does not usually cause symptoms. Most cases are found by this test.
Pregnant with one of these and not offered a test? Ask your midwife.
What happens during a GTT blood test?
Your morning at the clinic
- 1
Fasting blood test
In the morning, after a night without food.
- 2
Sugar drink
You drink it over about five minutes.
- 3
Two hours’ rest
Sit quietly. No walking about and no smoking.
- 4
Second blood test
Two hours after the drink. Results usually take a few days.
Sources: NHS; NHS pathology; Diabetes UK
The NHS says it takes about 2 hours. Bring a book or something to watch.
The drink can make you feel sick, and now and then people vomit. Tell the staff if you feel unwell.
Once it’s done, the lab advises you eat and drink before you leave. Pack a snack.
How do I prepare for a glucose tolerance test?
Before your glucose tolerance test
- Eat your normal diet, carbs included, for at least 3 days before. Cutting carbs can change the result.
- Stop eating the night before, for as long as your letter says.
- Drink only water while you fast, unless your letter allows black tea or coffee.
- Don’t smoke during the test.
- Tell the clinic if you take water tablets, beta-blockers (a heart and blood pressure medicine), steroids or the epilepsy medicine phenytoin.
- Pack a snack and a drink for after the second blood test.
Sources: NHS; NHS pathology
Fasting times differ. The NHS pregnancy page says 8 to 10 hours. One NHS lab asks for 10 to 16.
Those medicines can weaken the test. Never stop or change a prescribed medicine without your prescriber.
So can weeks of very little activity, being stuck in bed for days, a recent operation or illness, and fear of needles. Mention any of these when you book. More tips in how to prepare for a blood test.
When to speak to a GP
Not everyone with type 2 diabetes has symptoms. Book an appointment if:
- You feel very tired, pee more than usual, feel thirsty all the time or lose weight without trying.
- You think you may have type 2 diabetes, or you’re at higher risk of it.
- You’re pregnant, have a risk factor for gestational diabetes, and haven’t been offered a GTT.
- You had gestational diabetes, your sugar went back to normal after the birth, and you haven’t had a fasting sugar test 6 to 13 weeks after. NICE says a GTT isn’t routinely needed then.
- You had a result in the diabetes range without symptoms, and no repeat test was arranged.
Call 999 or go to A&E if you think your blood sugar is high and you feel sick, are being sick or have stomach pain. The same goes if you’re breathing faster or your heart is beating faster than usual.
Also call if you feel drowsy, confused or can’t concentrate. The same goes for breath that smells fruity like pear drops, or high ketones in your blood or pee. Don’t drive yourself.
See also blood sugar after eating and diabetes blood tests.