You passed your glucose test if your blood sugar came back below the cutoff your provider uses, which is typically 140 mg/dL for the one-hour screening and 140 mg/dL at the two-hour mark for a standard tolerance test. The tricky part is that not every clinic uses the same threshold, and results can take up to a day to appear. Here’s how to read your numbers and understand what they mean.
One-Hour Glucose Screening Cutoffs
Most people searching this question just drank the sugary glucose drink at their OB’s office and are waiting to find out what happened. This one-hour test, called the glucose challenge test, is a screening done during pregnancy (usually between weeks 24 and 28). You drink a 50-gram sugar solution, and your blood is drawn one hour later.
The most widely used passing threshold is below 140 mg/dL (7.8 mmol/L). If your result is under that number, you passed, and no further testing is needed. However, some clinics and labs set the bar lower at 130 mg/dL or 135 mg/dL. Your provider’s office can tell you which cutoff they use. If you’re checking results on a patient portal and see a number below 130, you can be confident you passed regardless of which standard your clinic follows.
A result between 140 and 189 mg/dL doesn’t mean you have gestational diabetes. It means you need a longer, more detailed follow-up test to find out. A result of 190 mg/dL or higher, on the other hand, is high enough to indicate gestational diabetes without further testing.
Three-Hour Follow-Up Test Thresholds
If your one-hour screening came back high, your provider will schedule a three-hour oral glucose tolerance test. For this one, you fast overnight (10 to 16 hours), then drink a stronger glucose solution. Your blood is drawn four times: once fasting, then at one hour, two hours, and three hours.
Under the most commonly used criteria (called Carpenter-Coustan), the cutoffs are:
- Fasting: 95 mg/dL
- 1 hour: 180 mg/dL
- 2 hours: 155 mg/dL
- 3 hours: 140 mg/dL
You need to meet or exceed at least two of those four values to be diagnosed with gestational diabetes. If only one value is elevated, or none are, you passed. Some providers use a slightly older set of thresholds that are a bit higher (105 fasting, 190 at one hour, 165 at two hours, 145 at three hours), but the two-out-of-four rule still applies. Ask your office which criteria they follow if your results are borderline.
If You’re Not Pregnant
Glucose tolerance tests aren’t only for pregnancy. A standard two-hour test is used to screen for type 2 diabetes and prediabetes in the general population. You fast, drink a 75-gram glucose solution, and have your blood drawn two hours later.
The CDC’s ranges for the two-hour result are straightforward: 140 mg/dL or below is normal, 140 to 199 mg/dL falls in the prediabetes range, and 200 mg/dL or above indicates diabetes. If your number is under 140, you passed.
When to Expect Your Results
Lab turnaround for glucose tests is typically within one day from when the lab receives your sample. Many results post to online patient portals the same evening or the next morning. If your provider’s office calls you, they usually reach out within a few business days, and in many practices, no call means normal results. If you haven’t heard anything after a week, it’s reasonable to call and ask.
When you see your results online, look for the number in mg/dL (the standard unit in the United States) alongside a reference range printed by the lab. If your value falls within that reference range, the result is normal. Labs outside the U.S. often report in mmol/L instead. To convert, multiply mmol/L by 18 to get mg/dL, or multiply mg/dL by 0.0555 to get mmol/L.
What Can Throw Off Your Results
A borderline or unexpectedly high result doesn’t always reflect your true blood sugar regulation. Several factors can temporarily impair glucose tolerance and push results higher than they’d normally be.
For accurate results, you should eat at least 150 grams of carbohydrates per day for the three days leading up to the test. That’s roughly the equivalent of eating your normal diet without cutting carbs. If you’ve been restricting carbohydrates or dieting in the days before, your body may respond more sluggishly to the glucose load, producing a falsely elevated reading. Vigorous or unusual exercise during those three days can also skew things.
Being sick matters too. Infections, injuries, and acute illness all raise blood sugar independently, so testing during a cold or stomach bug can produce misleading numbers. Certain medications, particularly steroids and some blood pressure pills, can also impair glucose tolerance. Physical inactivity and bed rest have the same effect, which is why the test is designed for people who are up and moving around in their daily lives, not hospitalized patients.
If you know any of these factors applied to you and your result came back borderline, mention it to your provider. A retest under better conditions may give a more accurate picture.
How You Felt During the Test Doesn’t Predict Results
Many people feel nauseous, jittery, or lightheaded after drinking the glucose solution, and they worry those symptoms mean their blood sugar spiked dangerously. In reality, dumping a concentrated sugar drink into an empty or near-empty stomach commonly causes nausea and a rapid energy surge regardless of whether you have a blood sugar problem. Feeling terrible during the test is not a sign you failed, and feeling fine is not a guarantee you passed. The only reliable indicator is the number on your lab report.
True high blood sugar symptoms, like extreme thirst, frequent urination, headaches, and blurred vision, develop when blood sugar stays elevated over longer periods. A brief spike during a one-hour test rarely produces those effects in a noticeable way.