The best way to pass a diabetes test is to follow the preparation instructions exactly and make sure nothing artificially inflates your blood sugar on test day. That means fasting for the right amount of time, staying hydrated, sleeping well, and managing stress. Some factors that raise your results have nothing to do with diabetes at all, and knowing about them ahead of time can prevent a false scare or an unnecessary retest.
It’s worth being direct: there’s no trick that will make a genuinely high blood sugar look normal, and you wouldn’t want one. But plenty of people get borderline or elevated results because of dehydration, poor sleep, medication side effects, or testing at the wrong time of day. Controlling those variables gives you the most accurate reading possible.
Know Which Test You’re Taking
Diabetes screening uses three main tests, and each one measures something different. The preparation rules depend on which one your doctor ordered.
- Fasting blood glucose measures your blood sugar after you haven’t eaten for 8 to 12 hours. A normal result is under 100 mg/dL. Between 100 and 125 mg/dL falls into the prediabetes range, and 126 mg/dL or higher indicates diabetes.
- A1C test measures your average blood sugar over the past three months by checking how much sugar has attached to the hemoglobin in your red blood cells. Normal is below 5.7%, prediabetes is 5.7% to 6.4%, and diabetes is 6.5% or higher. Because red blood cells regenerate roughly every three months, this test reflects a long window and can’t be influenced by what you did in the last few days.
- Oral glucose tolerance test (OGTT) requires you to drink a solution containing 75 grams of glucose, then have your blood drawn two hours later. This test shows how efficiently your body clears sugar from the bloodstream. A two-hour reading under 140 mg/dL is normal, 140 to 199 is prediabetes, and 200 or above is diabetes.
The A1C doesn’t require fasting. The other two do. If your doctor is running additional labs like cholesterol alongside an A1C, you may still need to fast for those.
Follow the Fasting Rules Precisely
For a fasting glucose test or OGTT, don’t eat or drink anything except water for 8 to 12 hours before the test. That means no coffee, no juice, no gum with sugar. Even a small amount of calories can trigger an insulin response and throw off your numbers.
Most people schedule fasting tests first thing in the morning so the fasting window overlaps with sleep. If your appointment is at 8 a.m., stop eating by midnight at the latest. Water is fine and actually encouraged throughout the fasting period.
Stay Well Hydrated
Dehydration concentrates glucose in your blood and can push your results higher than they should be. Research on people with type 2 diabetes found that just three days of restricted water intake significantly raised blood sugar readings during a glucose tolerance test. The dehydrated group had notably higher glucose at both the fasting measurement and the two-hour mark compared to when they were properly hydrated. The effect was driven by increased cortisol, a stress hormone that raises blood sugar on its own.
Drink water normally in the days leading up to your test, and have a glass or two the morning of. You don’t need to overhydrate, just don’t show up thirsty.
Watch Out for the Dawn Phenomenon
Your body naturally releases a wave of hormones between about 4 a.m. and 8 a.m., including cortisol, growth hormone, and glucagon. These hormones increase insulin resistance and push blood sugar up. This is called the dawn phenomenon, and it’s a normal part of human biology, but it can bump a fasting glucose reading a few points higher than it would be later in the morning.
If your test is scheduled very early, this may work against you. There’s not much you can do about it, but it’s useful to know. If you get a borderline fasting result, this could be part of the reason, and your doctor may want to confirm with a second test or an A1C.
Get Enough Sleep the Night Before
Sleep deprivation raises stress hormones, which in turn raise blood sugar. Even one night of poor sleep can temporarily reduce your body’s ability to respond to insulin. This won’t turn a normal result into a diabetic one, but if you’re on the border, it could push you into prediabetes range unnecessarily.
Aim for a normal night of sleep before your test. If you’re anxious about the appointment, try to keep your evening routine as calm and consistent as possible.
How Exercise Affects Your Results
A single session of exercise improves your body’s insulin sensitivity for up to 72 hours afterward. That means if you go for a brisk walk or do a workout the day before your test, your muscles will be more efficient at pulling sugar out of your bloodstream, and your glucose readings may come in lower.
This is a real physiological effect, not a gimmick. Researchers have noted that if a sedentary person exercises the day before a glucose tolerance test, the lingering improvement in insulin sensitivity could mask what would otherwise be an elevated reading. That’s something to be aware of in both directions. If you’re normally active, don’t stop exercising before the test, because your results should reflect your usual lifestyle. If you never exercise and suddenly do a hard workout the night before, you’re getting a reading that doesn’t represent your everyday reality.
The most honest approach: maintain your normal activity level in the days before testing. If you’ve been meaning to start walking regularly, starting a few months before the test and sticking with it will genuinely lower your blood sugar over time, not just for one day.
Medications That Raise Blood Sugar
Several common medications can push glucose levels up, sometimes enough to tip a borderline result into abnormal territory. The most well-known culprits are corticosteroids like prednisone, prednisolone, and dexamethasone. All forms of corticosteroids carry this risk at high doses, and even a joint injection can cause a blood sugar spike within 24 to 72 hours.
Other medications that can raise fasting glucose include thiazide diuretics (often prescribed for blood pressure), beta blockers like metoprolol and atenolol, certain antipsychotics, and statins. Beta blockers carry a 22% increased risk of new-onset diabetes diagnosis, partly because some types reduce blood flow to muscles and slow down glucose uptake.
If you’re taking any of these and have a diabetes test coming up, don’t stop your medication on your own. But do tell your doctor what you’re on so they can interpret the results in context. A slightly elevated reading in someone taking prednisone means something very different from the same number in someone on no medications.
Stress and Illness Can Spike Your Numbers
Acute stress triggers your body to release cortisol and adrenaline, both of which raise blood sugar as part of the fight-or-flight response. If you’re going through an unusually stressful period, dealing with an illness, or recovering from an injury, your glucose levels may be temporarily higher than your true baseline.
Being sick is a particularly strong trigger. Infections and injuries cause inflammation that increases insulin resistance. If you’ve been unwell in the days before your test, mention it to your doctor. They may suggest retesting once you’ve recovered to get a cleaner picture.
What You Can’t Change in a Few Days
The A1C test reflects three months of blood sugar history. No amount of fasting, exercising, or hydrating in the week before will meaningfully move that number. If your doctor has ordered an A1C, the result is going to show your average blood sugar over the past quarter, full stop.
That’s actually useful information. If your A1C is elevated, it’s telling you something real about how your body has been handling sugar. The fasting glucose and OGTT are more vulnerable to day-of variables, which is why doctors often use more than one test to confirm a diagnosis.
Longer-Term Preparation That Actually Works
If your test is weeks or months away and you want to genuinely improve your numbers, the evidence points to a few consistent changes. Regular physical activity improves insulin sensitivity not just in the hours after a workout but as an ongoing adaptation when you stick with it. Walking 30 minutes most days is enough to make a measurable difference.
Reducing refined carbohydrates and added sugar lowers the glucose load your body has to process after meals, which directly lowers both your fasting glucose and A1C over time. Losing even a modest amount of weight, around 5 to 7% of your body weight, significantly reduces the risk of progressing from prediabetes to diabetes.
These changes won’t help you pass a test tomorrow, but they’re the only things that will actually change what the test is measuring rather than just optimizing the conditions around it.