You’re thirsty. Not just "I forgot my water bottle" thirsty, but a bone-deep, desert-dry parched feeling that won't go away no matter how many glasses of water you chug. Maybe you’re also running to the bathroom every twenty minutes. You might shrug it off as a salty dinner or too much coffee, but these are often the first quiet whispers of hyperglycemia. Knowing how to know if blood sugar is high isn't always about a dramatic medical emergency; it’s usually about spotting the subtle ways your body starts to glitch when there’s too much glucose floating around in your bloodstream.
It's tricky. Honestly, some people walk around with blood sugar levels in the 200s or 300s for months—even years—without realizing anything is actually wrong. They just think they’re getting older or working too hard.
The biological reality is pretty straightforward. When your insulin isn't working right, or you don't have enough of it, sugar stays in your blood instead of fueling your cells. Your kidneys then try to flush that excess sugar out through your urine, which drags water along with it. This is why the cycle of drinking and peeing is the classic "red flag" duo. But there is a lot more to the story than just thirst.
The Physical "Tells" of Hyperglycemia
If you want to understand the physical cues, you have to look at your skin and your energy. Ever notice a weird, dark, velvety patch on the back of your neck or in your armpits? Doctors call that acanthosis nigricans. It’s basically your skin reacting to high levels of insulin or glucose. It isn't dirt. It won't scrub off. It’s a metabolic billboard.
Then there’s the vision issue. High sugar can cause the lenses in your eyes to swell. This changes your ability to focus. If your vision feels "blurry" one day and fine the next, that’s a massive hint that your glucose is swinging wildly.
Fatigue is another one, but it’s a specific kind of tired. It’s that heavy, lead-in-your-veins exhaustion that hits right after a meal. While a "food coma" is common for everyone, the hyperglycemic version is more intense because your cells are literally starving for energy while the "fuel" (sugar) is stuck outside the door.
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Why Your Breath Might Smell Like Fruit
It sounds weird, right? Fruity breath. Like you've been eating Juicy Fruit gum or drinking cheap cider. This is a specific sign of something called DKA, or Diabetic Ketoacidosis.
When the body can't use sugar for energy, it starts burning fat at a terrifyingly fast rate. This process produces ketones. One of those ketones is acetone—the same stuff in nail polish remover. If you smell that on your breath, or if someone else mentions it, you aren't just "high"—you are moving into a medical danger zone. It’s often accompanied by nausea or stomach pain that people mistake for the flu. Don't make that mistake.
Using Technology: The Only Way to Be Certain
Look, you can guess based on symptoms all day, but if you really want to figure out how to know if blood sugar is high, you need data. Subjective feelings are notoriously unreliable. I've seen people feel "low" when they are actually at 250 mg/dL because their body has become so used to being at 400 mg/dL. Their internal thermostat is broken.
Finger-Stick Glucometers
The old-school way. Prick the finger, drop of blood, wait five seconds.
- Fasting: If you wake up and you're over 126 mg/dL, that’s technically the clinical cutoff for diabetes.
- Post-Meal: If you're over 180 mg/dL two hours after eating, your body is struggling to process that load.
Continuous Glucose Monitors (CGM)
This is the gold standard for 2026. Devices like the Dexcom G7 or the Abbott Freestyle Libre 3 give you a literal graph on your phone. You can see the exact moment that bowl of pasta sent you into the stratosphere. It removes the guesswork. You start to see patterns—like how stress at work can spike your sugar just as much as a donut can.
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The Psychological Side: "Sugar Grumpiness"
We talk a lot about the physical, but high blood sugar wreaks havoc on your brain. Brain fog is real. You might find yourself staring at an email for ten minutes, unable to string a sentence together.
Irritability is the other side of that coin. Ask the partner of anyone with undiagnosed Type 2 diabetes; they’ll tell you about the "snaps." When blood sugar is high, the brain is essentially inflamed and poorly fueled. You become impatient, short-tempered, and generally "over it." If you find yourself biting someone's head off for no reason, check your levels. It might not be your personality; it might be your pancreas.
Yeast Infections and Slow Healing
High sugar makes your blood a literal petri dish for bacteria and fungi. They love sugar. If you find yourself dealing with recurring yeast infections or "jock itch" that won't quit, your sugar is likely high.
Check your feet, too. If a small scratch from three weeks ago is still red and hasn't scabbed over properly, that's a sign of poor circulation and high glucose interfering with the body's natural repair mechanisms. This is how minor issues turn into "diabetic ulcers." It happens slowly, then all at once.
What Most People Get Wrong About "The Crash"
A lot of people think they have high blood sugar because they feel shaky and sweaty. Actually, those are usually signs of low blood sugar (hypoglycemia) or a "reactive" drop.
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High blood sugar usually feels "heavy" and "dry." Low blood sugar feels "frantic" and "wet" (sweaty). Understanding that distinction is huge. If you treat a "high" as if it were a "low" by eating more sugar, you’re throwing gasoline on a fire.
Immediate Actionable Steps
If you suspect your levels are elevated, don't panic, but do move.
- Hydrate immediately. Drink plain water. Avoid juices or sodas (obviously). Water helps the kidneys filter out the excess.
- Go for a walk. Muscle contraction is one of the few ways your body can move sugar out of the blood without needing extra insulin. A 20-minute brisk walk can drop your numbers significantly.
- Check your labels. You’d be shocked how many "healthy" green juices have 40 grams of sugar.
- Get an A1c test. This is a simple blood test at the doctor that shows your average sugar over the last three months. It’s the "cheat sheet" for your metabolic health.
Beyond the Basics
Sometimes, high sugar isn't about what you ate. It can be the "Dawn Phenomenon," where your liver dumps sugar into your system at 4:00 AM to help you wake up. Or it could be a side effect of a steroid medication like Prednisone.
If you're consistently seeing high numbers despite "eating right," it’s time to look at cortisol and stress. Chronic stress keeps you in a "fight or flight" mode, and your body stays flooded with glucose to give you the energy to "fight" a tiger that doesn't exist. Your body doesn't know the difference between a predator and a past-due mortgage.
Final Reality Check
The only definitive way to know your status is through clinical testing. If you are experiencing extreme thirst, frequent urination, and unexplained weight loss (where you’re eating more but getting thinner), go to an urgent care or your primary doctor immediately. These can be signs of Type 1 diabetes or severe Type 2, which require professional intervention to avoid a coma.
Next Steps for You:
- Buy an over-the-counter glucose meter at any pharmacy; they usually cost about $20.
- Test yourself first thing in the morning and again two hours after your largest meal.
- Keep a log for three days. If you see numbers consistently above 140 mg/dL, book an appointment with a healthcare provider to discuss a formal A1c test.
- Prioritize sleep, as even one night of poor rest can cause temporary insulin resistance the following day.