Checking your blood sugar takes about 30 seconds once you have the right supplies: a blood glucose meter, test strips, a lancing device, and lancets. The process involves pricking the side of your fingertip, touching a test strip to the blood drop, and reading the number on your meter’s screen. If you’re doing this for the first time, the steps below will walk you through it clearly.
What You Need Before You Start
A basic blood glucose monitoring kit includes four things: a meter, test strips compatible with that meter, a lancing device (the spring-loaded tool that holds the needle), and disposable lancets. Most kits sold at pharmacies bundle these together. You’ll also want soap and water nearby, or alcohol pads and a tissue as a backup for cleaning your finger.
Test strips are the ongoing cost. They’re specific to your meter brand, so double-check compatibility before buying. Strips can be damaged by moisture, so store them in their original container with the cap closed, and don’t handle them with wet hands.
Step-by-Step Finger Stick Testing
Wash your hands with soap and water and dry them thoroughly. Even small amounts of moisture on your fingers can damage the test strip or skew your reading. If you recently handled fruit, juice, or anything sugary, washing is especially important because residue on your skin can artificially raise the result.
Prepare your lancing device by inserting a fresh lancet and setting the puncture depth. Most devices have a dial ranging from 1 to 5. Start at level 1 or 2. You can increase the depth later if you’re not getting enough blood, but a shallower prick hurts less and heals faster.
Insert a test strip into your meter’s port with the contact end going in first. The meter should beep and turn on automatically, displaying a symbol that means it’s ready for blood. Then choose a finger. The side of your fingertip is the recommended spot because it has good blood flow and fewer nerve endings than the pad. Rotate fingers between tests to avoid soreness.
Press the lancing device firmly against the side of your fingertip and hit the release button. Pull it away immediately. You should see a small blood drop forming. If the drop is too small, gently squeeze your finger from the base toward the tip rather than pressing right at the puncture site. Touch the narrow tip of the test strip directly to the blood drop. The strip draws blood in through capillary action, so you don’t need to smear or press. Putting blood on the top, bottom, or flat side of the strip won’t work. Within a few seconds, your reading appears on the screen.
What Your Numbers Mean
Blood sugar is measured in milligrams per deciliter (mg/dL) in the United States. General targets for most adults with diabetes are 80 to 130 mg/dL before meals and below 180 mg/dL one to two hours after eating, though your individual targets may differ based on your treatment plan.
Your meter gives you a snapshot of that exact moment. For a longer view, your doctor orders an A1C test every few months, which reflects your average blood sugar over roughly 90 days. An A1C of 7% corresponds to an average blood sugar of about 154 mg/dL. At 8%, that average climbs to around 183 mg/dL. At 6.5%, it’s approximately 140 mg/dL. Tracking both your daily readings and your A1C gives you the full picture of how well your blood sugar is managed over time.
How Often to Test
Testing frequency depends entirely on your type of diabetes and how you manage it. If you have type 1 diabetes, expect to test 4 to 10 times a day: before meals and snacks, before and after exercise, and sometimes after meals. A continuous glucose monitor (more on that below) can reduce the number of finger sticks.
If you have type 2 diabetes and use insulin, you’ll typically test several times a day. People on multiple daily insulin injections often test before meals and at bedtime. Those using a single long-acting insulin may only need to test before breakfast and occasionally before dinner. If you manage type 2 diabetes without insulin, through oral medications, diet, or exercise, you may not need to test every day. Your doctor will help you decide on a schedule that makes sense.
Testing From Other Body Sites
Some meters allow you to draw blood from the upper arm, forearm, base of the thumb, or thigh instead of your fingertip. This can be useful if your fingertips are sore from frequent testing. But alternative sites have a significant limitation: they lag behind fingertip readings when your blood sugar is changing quickly.
Stick with your fingertip if you think your blood sugar might be low, if you’ve just eaten or exercised, if you’re feeling ill or stressed, or if the alternative site result doesn’t match how you feel. Not all meters support alternative site testing, so check your device’s instructions before trying it.
Continuous Glucose Monitors
A continuous glucose monitor, or CGM, is a small sensor worn on your body (usually the back of your upper arm or abdomen) that measures blood sugar in the fluid just beneath your skin every few minutes. It sends readings to your phone or a receiver, giving you a real-time trend line instead of isolated snapshots. Most sensors last 10 to 14 days before replacement.
CGMs are accurate enough for daily decision-making, though they measure interstitial fluid rather than blood directly, which means there’s a slight delay compared to a finger stick. Current-generation sensors from major manufacturers typically fall within about 10 to 15% of a finger-stick reading. You may still need occasional finger sticks to calibrate some models or to confirm a reading that seems off.
Be aware that certain substances can interfere with CGM accuracy. High doses of acetaminophen (the active ingredient in Tylenol) can cause falsely elevated readings on Dexcom and Medtronic sensors. High-dose vitamin C can do the same on FreeStyle Libre sensors. If you take either of these regularly, a finger-stick confirmation is a good idea. All CGM sensors also need to be removed before MRI, CT, or X-ray imaging.
Common Reasons for Inaccurate Readings
If a reading seems wrong, the most common culprits are simple and fixable. Residue on your hands, especially from food, lotion, or hand sanitizer, is the number one cause of unexpectedly high readings. Always wash and dry your hands first. Expired or improperly stored test strips are another frequent issue. Heat, humidity, and leaving the cap off the strip container all degrade accuracy.
Squeezing your fingertip too hard can dilute the blood sample with tissue fluid, producing a falsely low result. A gentle massage from the base of the finger works better than clamping down right at the puncture. If your meter allows coding and you’ve inserted a new batch of strips, make sure the code matches. And if a result doesn’t match how you feel, test again with a fresh strip before making any treatment decisions.
Disposing of Lancets Safely
Used lancets are classified as sharps and shouldn’t go directly into your household trash. Place them immediately into a sharps disposal container, which you can buy at most pharmacies for a few dollars. A thick plastic laundry detergent bottle with a screw cap works in a pinch. Fill the container to about three-quarters full, then seal it.
Disposal options for full containers vary by location. Many pharmacies, hospitals, fire stations, and health departments serve as drop-off sites. Some communities offer mail-back programs or special waste pickup services. You can find disposal options specific to your area by calling Safe Needle Disposal at 1-800-643-1643.