Ever since my dad came back from the hospital with the word “diabetes” thrown at him, our family got a personal glucose meter for each person. But my dad keeps insisting he doesn’t have diabetes—he’s had “these numbers for 10 years,” according to him. Still, would the doctor have prescribed Metformin for no reason? My dad’s HbA1c is 6.2%, which is officially classified as prediabetes. But one doctor I respect once said that even 6.3% is “basically diabetes.” Plus, his fasting glucose at the hospital came back at 130, so whether you call it diabetes or prediabetes, it makes sense to treat it like diabetes. I’m pretty sure the doctor thought the same, especially since he also has high blood pressure and high cholesterol.

My mom’s numbers are closer to the normal side of prediabetes. She has a retinal condition, so vascular health is critically important. That’s why I got her a separate glucose meter, and I keep one for myself too, partly to stay aware.

Why Are Blood Glucose Test Strips So Expensive?

When you buy a glucose meter, it usually comes as a set with the device and some test strips. But once you use up the strips, you have to buy new ones separately. Like a printer with its ink cartridges, the device is cheap but the consumables are pricey. Test strips are exactly that kind of product. Considering you need to test daily, it really does feel expensive.

Test strips barely work with other brands’ meters. That means you have to use the brand’s strips with its own meter. You can’t use an A-brand meter with B-brand strips. (Not an ad, I swear.) I use Boryung’s meter and strips from Coupang, which are almost half the price of other brands.

Questions That Come Up While Checking Blood Sugar

When you check your blood sugar at home, a couple of questions always pop up: “Why does my reading change every time?” and “Why is my fasting sugar so high?” Fasting sugar is a whole topic on its own, so here I’ll focus on why the readings fluctuate.

Why Does My Reading Change Every Time?

The first reason my parents started doubting their glucose meters is this. Usually, when the reading looks “good,” nobody bothers to double-check. (Funny, right?) But if it comes out higher than expected, they go, “Hmm, that can’t be right,” and check again for peace of mind. And then—boom—it sometimes reads 10–20 points lower. Naturally, the reaction is:

This thing is totally unreliable!

So why does this happen? It turns out that glucose meters and their strips have built-in tolerances, and various conditions affect the results.

• Moisture, lotion, or food residue on your fingers can skew readings up or down.
• Massaging or squeezing your finger too hard to get blood out can alter blood composition slightly and affect the number.
• Blood sugar naturally fluctuates throughout the day—after meals, after moving around, and even from stress or mood.

"But I retested immediately under the same conditions!"

• (Key point) Glucose meters and strips usually allow about a ±15% margin of error. The enzymes on the strip are sensitive to humidity and temperature, and if the blood drop is too small, readings can swing.

To really understand this, let’s see how a home glucose meter actually works.

How a Home Glucose Meter Actually Works

The principle is simpler than you might think. The tip of the test strip has tiny electrodes. When you place a drop of blood from a finger prick, the glucose in the blood reacts with enzymes on the strip. This reaction produces a tiny electrical current, which the device measures and translates into your blood sugar level.

The catch is that this current is extremely small, so even tiny environmental factors or the condition of that single drop of blood can affect the result. If the blood drop is too small or starts to dry, the reaction won’t work fully and the reading might come out low. Moisture or lotion on your finger can mix with the blood and skew the reading high or low. Leaving strips exposed to air too long weakens the enzymes, which also causes fluctuations.

That’s why even at the same time, under slightly different conditions, you might see a 10–20 mg/dL difference. This is why home meters can’t perfectly match hospital lab tests.

So, for home testing, keeping conditions consistent is key. Wash and dry your hands thoroughly, wipe away the first drop, and use the second drop for testing for more stable results. Always check the strip’s expiration date and storage conditions. And most importantly, focus on the trend rather than obsessing over single readings.

If Accuracy Isn’t Perfect, Is Home Testing Useless?

From my experience, home glucose meters are still very meaningful for spotting trends. For example, if my mom and I eat the same meal and test together, my healthier blood sugar comes out much lower. And if I get a higher reading one day, I can do some strength training and retest—it clearly drops. A single number might not always be precise, but the pattern those numbers form is definitely useful, as long as you test regularly and under similar conditions.

One of the main reasons to check blood sugar is to stay aware. Some people eat carelessly and get high fasting glucose on checkups but stay in denial. Why? Because once you start caring about your health, endless worries can follow. It feels easier to ignore it. But seeing your own numbers makes awareness almost automatic.

Suddenly, that delicious bread or rice cake just looks like “carbs,” and that refreshing soda makes you think about how the high-fructose syrup will hit your body. The image pops up in your mind without trying.

Don’t get anxious over a single reading. But getting into the habit of testing and observing trends—that’s the real value.