The glucose test uses either 50 grams, 75 grams, or 100 grams of sugar, depending on which version your provider orders. Most people searching this question are pregnant and preparing for a gestational diabetes screening, which typically starts with a 50-gram drink. Here’s what each version involves and what to expect.
Sugar Amounts for Each Test Version
There are three standard glucose test doses, and each serves a different purpose:
- 50 grams: The initial screening for gestational diabetes. This is the one most pregnant people take first, usually between weeks 24 and 28. It’s a one-hour test, and you don’t need to fast beforehand.
- 75 grams: Used to diagnose type 2 diabetes and prediabetes in non-pregnant adults. This is a two-hour test that requires fasting for 8 to 14 hours. Some providers also use this as a single-step gestational diabetes screen instead of the two-step approach.
- 100 grams: The three-hour follow-up test for gestational diabetes. You only take this if your 50-gram screening comes back high. It also requires fasting for 8 to 14 hours.
For children, the dose is calculated by weight: 1.75 grams of glucose per kilogram of body weight, up to a maximum of 75 grams.
What’s Actually in the Drink
The glucose drink (often sold under the brand name Trutol) contains water, dextrose, citric acid, and flavoring. The sugar is 100% dextrose derived from corn, not high fructose corn syrup. It comes in flavors like lemon-lime, orange, and fruit punch, which are made from natural fruit oils and extracts. The texture is similar to a flat, very sweet soda.
To put the sugar content in perspective, 50 grams is roughly the amount in a 20-ounce bottle of cola. The 75-gram version is like drinking that same bottle plus another half. And the 100-gram drink packs the sugar equivalent of about two full bottles of soda into a much smaller, more concentrated serving, which is why many people find it intensely sweet. You’re typically asked to finish it within five minutes.
How the Two-Step Pregnancy Screening Works
The most common approach to gestational diabetes testing uses two steps. First, you drink the 50-gram glucose solution without any fasting. Your blood is drawn one hour later. If your blood sugar comes back above a certain threshold, that doesn’t mean you have gestational diabetes. It means you need the longer follow-up test.
For the second step, you fast overnight (8 to 14 hours), then drink the 100-gram solution. Blood is drawn before the drink and at one, two, and three hours afterward. Your provider checks all four values to determine whether gestational diabetes is present. This three-hour version is more definitive but also more demanding on your body, since you’re consuming a large sugar load on an empty stomach.
A less common alternative skips the initial 50-gram screen entirely and goes straight to a 75-gram, two-hour fasting test. This single-step method is used by some practices and gives a definitive result in one visit.
How the 75-Gram Test Diagnoses Diabetes
Outside of pregnancy, the standard oral glucose tolerance test uses 75 grams of sugar and lasts two hours. You fast overnight, get a baseline blood draw, drink the solution, then have blood drawn again at the two-hour mark. According to the American Diabetes Association, the results break down like this:
- Normal: Blood sugar below 140 mg/dL at two hours
- Prediabetes: 140 to 199 mg/dL at two hours
- Diabetes: 200 mg/dL or higher at two hours
This test measures how efficiently your body clears sugar from the bloodstream. A high reading means your cells aren’t responding well to insulin, the hormone that moves sugar out of your blood and into your tissues for energy.
What the Experience Feels Like
The drink itself is the hardest part for most people. It’s extremely sweet and syrupy, and you need to get it down quickly. Nausea is common, especially with the 75-gram and 100-gram versions taken on an empty stomach. Some people feel lightheaded, shaky, or sweaty during the waiting period, which is a normal response to a rapid spike and drop in blood sugar.
For the one-hour, 50-gram screening, you’ll spend about an hour sitting in the office or lab after drinking. For the three-hour test, expect to be there for the full three hours with multiple blood draws. Bringing something to read or watch can help pass the time. You’ll be able to eat and drink normally as soon as your final blood sample is taken.