Checking your blood sugar takes about 30 seconds using a small portable device called a glucometer and a drop of blood from your fingertip. The process is straightforward once you’ve done it a few times, and most people test themselves at home without any medical training. Here’s exactly how to do it, what your numbers mean, and how to get accurate results.
Step-by-Step Fingerstick Testing
A glucometer kit includes the meter itself, a lancing device (a spring-loaded tool that pricks your skin), disposable lancets, and test strips. You can buy these at any pharmacy without a prescription. Once you have your supplies, the process works like this:
- Make sure your meter is charged and has a test strip inserted.
- Wash your hands with soap and warm water, then dry them completely. Residue on your skin, even from food or lotion, can throw off your reading. Don’t use hand sanitizer as a substitute.
- Massage or shake your hand to push blood toward your fingertips. If your hands are cold, warm them up first, since cold fingers restrict blood flow and make it harder to get a usable drop.
- Load a fresh lancet into the lancing device and prick the side of your fingertip. The side hurts less than the pad because it has fewer nerve endings.
- Squeeze gently from the base of your finger until a round drop of blood forms. Touch it to the test strip in one motion. Don’t try to add more blood after the first application.
- Wait a few seconds for the reading to appear on the screen.
- Record the result along with the time and any notes about meals, exercise, or anything else that might have influenced the number.
- Dispose of the lancet and test strip safely.
Rotate which finger you use to avoid building up sore spots. Most people find the ring finger and middle finger easiest to work with.
What Your Numbers Mean
The American Diabetes Association recommends the following targets for most adults with diabetes: 80 to 130 mg/dL before a meal, and less than 180 mg/dL one to two hours after the start of a meal. For people without diabetes, fasting blood sugar typically falls between 70 and 100 mg/dL.
Two thresholds are worth knowing. A reading below 70 mg/dL counts as low blood sugar (hypoglycemia), and you should treat it right away with fast-acting carbohydrates like juice or glucose tablets. Below 40 mg/dL is considered severe hypoglycemia and requires immediate help. On the high end, readings consistently at or above 180 mg/dL signal that your management plan may need adjusting.
A single reading that looks off isn’t necessarily cause for alarm. Stress, illness, a recent meal, or even a dirty fingertip can skew results. If a number surprises you, wash your hands and test again before reacting.
When and How Often to Test
Your testing schedule depends on your type of diabetes and your treatment plan. People using insulin, especially those with Type 1 diabetes, typically test four or more times a day: before meals and at bedtime. If you’re managing Type 2 diabetes with oral medications or lifestyle changes alone, your doctor may recommend testing once or twice a day, or only on certain days of the week.
The most common testing times are first thing in the morning before eating (your fasting level), before meals, one to two hours after meals (to see how food affects your blood sugar), and before bed. Testing before and after the same meal for a few days in a row can reveal how specific foods affect you, which is more useful than random spot checks.
Continuous Glucose Monitors
A continuous glucose monitor (CGM) is a small sensor worn on your body, usually the back of your upper arm, that measures glucose levels automatically throughout the day. Instead of pricking your finger, the sensor sits just under the skin and reads glucose in the fluid between your cells, then sends the data wirelessly to your phone or a receiver.
Depending on the device, sensors last anywhere from 10 to 14 days before replacement, though implantable versions can stay in place for up to 90 days. CGMs are especially useful for spotting patterns you’d miss with fingerstick testing, like blood sugar dips overnight or spikes you didn’t feel. Most CGMs still recommend confirming with a fingerstick if a reading doesn’t match how you feel, particularly when your blood sugar is changing quickly.
Testing From Alternate Sites
Some meters allow you to test from the palm, forearm, upper arm, thigh, or calf instead of your fingertip. This can be helpful if your fingertips are sore from frequent testing. Check your meter’s manual first, since not every device supports alternate sites.
The trade-off is accuracy during rapid changes. Sites like the forearm or thigh have less blood flow than fingertips, so readings can lag behind your actual blood sugar by 15 to 20 minutes when levels are rising or falling fast, such as after eating, exercising, or taking medication. Stick with your fingertip if you suspect a low, if you’ve just eaten, or if the reading doesn’t match how you feel.
Getting Accurate Results
Home meters are reliable, but several common mistakes can produce misleading numbers. The biggest one is testing with unwashed hands. Traces of fruit, sugar, or even hand lotion on your fingertip can artificially inflate your reading. Soap and water are the fix; alcohol wipes work only if you let the site dry completely before pricking.
Test strip storage matters more than most people realize. Strips are sensitive to moisture and temperature extremes. Keep them in their sealed container at room temperature, and never use strips past their expiration date. If you leave your kit in a hot car or a cold garage, the strips may give inaccurate readings.
Dehydration and anemia (a low red blood cell count) can also affect accuracy. If you’re sick, dehydrated, or know your red blood cell count is low, keep in mind that your readings may be less precise during those periods.
Finally, apply enough blood in one touch. A small or smeared drop is one of the most common reasons for error messages or unreliable numbers. If you’re not getting enough blood, try adjusting the depth setting on your lancing device or warming your hands before testing.
Safe Disposal of Lancets
Used lancets are sharp enough to pierce skin and should never go loose into your household trash. The FDA recommends placing them immediately into a sharps disposal container, which is a puncture-resistant plastic container you can buy at most pharmacies for a few dollars. A thick plastic laundry detergent bottle with a screw cap works in a pinch.
Once the container is about three-quarters full, seal it and dispose of it according to your local guidelines. Options vary by community but typically include drop-off sites at pharmacies, hospitals, or fire stations, household hazardous waste collection events, and mail-back programs. You can call 1-800-643-1643 (Safe Needle Disposal) or check with your local health department to find out what’s available near you.