Using a glucometer takes about 30 seconds once you get the hang of it: you prick the side of your fingertip, touch a test strip to the blood drop, and read your number on the screen. But the details of each step matter. Small mistakes in hand washing, strip storage, or lancing technique can throw off your results or make the process more painful than it needs to be. Here’s how to do it right from the start.
What You Need Before You Start
A basic glucose testing kit includes four things: the meter itself, test strips, a lancing device (the spring-loaded pen that holds the needle), and lancets (the small disposable needles that snap into it). Most kits come with all of these in the box. You’ll also want alcohol swabs or access to soap and water.
Before your first test, check whether your meter requires coding. Older meters need you to enter a code printed on each vial of test strips so the meter calibrates to that specific batch. The enzymes in test strips vary from batch to batch, and the code corrects for that variation. If you forget to update the code when you open a new vial, your readings can be off. Most newer meters are “no code,” meaning they read the calibration automatically from the strip or cartridge, so there’s nothing to enter. Check your meter’s manual to see which type you have.
Preparing Your Hands
Wash your hands with warm soap and water and dry them completely before testing. This isn’t just about hygiene. Residue on your skin, even trace amounts of sugar from food, can contaminate the blood sample and produce a falsely high reading. Hand sanitizer isn’t ideal because it can contain ingredients that interfere with the strip chemistry. Warm water also helps with blood flow, making it easier to get a usable drop from a finger prick.
Setting Up the Lancing Device
Twist or pull the cap off your lancing device and insert a fresh lancet. Snap or twist off the small protective cover on the lancet tip, then replace the device cap. Each lancet is meant to be used once. Reusing one dulls the needle, which makes the prick hurt more and can produce a less clean puncture.
Next, set the depth. Most lancing devices have a dial with settings ranging from 0 to 5 (some have up to 11 increments within that range). Higher numbers mean a deeper prick. A setting of about 3 is a good starting point for most people. If you don’t get enough blood, turn it up one notch. If it hurts more than a brief pinch, turn it down. People with thicker or more calloused skin generally need a higher setting, while thinner skin does fine at 1 or 2.
Getting a Blood Sample
Insert a test strip into your meter. Most meters turn on automatically when you do this and display a symbol indicating they’re ready for blood. Then cock the lancing device by pulling back the plunger or sliding the mechanism until it clicks.
Press the tip of the lancing device firmly against the side of your fingertip, not the pad. The sides of the finger have fewer nerve endings than the center pad, so lancing there hurts noticeably less. Use any finger, though the middle and ring fingers tend to work well. Avoid the thumb and index finger if possible since you use those constantly and soreness there is more disruptive. Press the release button.
After the prick, gently squeeze your finger from the base toward the tip to form a round blood drop. Don’t squeeze too hard or milk the finger aggressively. Forcing blood out can mix it with tissue fluid, which dilutes the sample and can lower your reading. You need a drop about the size of a small pinhead for most modern strips.
Applying Blood to the Strip
Touch the edge of the test strip’s sample area to the blood drop. Most strips use a capillary channel that wicks the blood in automatically, so you don’t need to smear or press. Hold the strip to the drop until the meter beeps or the screen shows it’s processing. This usually takes 3 to 10 seconds depending on the meter model.
If the meter displays an error, the most common cause is not enough blood on the strip. You’ll need to discard that strip, insert a new one, and try again. Some newer meters detect when the sample volume is sufficient and start the countdown automatically, which helps prevent this problem. Never try to add more blood to a strip after the meter has already started its reading.
Reading and Recording Your Results
Your blood sugar level appears on the screen in milligrams per deciliter (mg/dL) in the United States, or millimoles per liter (mmol/L) in many other countries. Double-check that your meter is set to the correct unit. Accidentally switching from mg/dL to mmol/L (or the reverse) is a known source of confusion, and the numbers look dramatically different. A reading of 100 mg/dL, for example, is the same as 5.6 mmol/L.
Most meters store your last several hundred readings with timestamps. Even so, many people find it helpful to log results in a notebook or app, especially if you’re tracking patterns around meals, exercise, or medication. Note what you ate and when, or anything unusual about the day, alongside the number.
Testing on Sites Other Than Fingertips
Some meters are approved for alternate site testing, meaning you can draw blood from your forearm, palm, or upper arm instead of your fingers. This can be more comfortable if your fingertips are sore from frequent testing. However, these sites have a significant limitation: blood from your forearm or palm lags behind your actual blood sugar when levels are changing quickly, such as after eating, after exercise, or during a low blood sugar episode. If a reading from an alternate site seems off, retest with a fingertip sample. Fingertip blood reflects your current glucose level most accurately.
Storing Test Strips Properly
Test strips are the most sensitive part of your kit. The enzymes on the strip degrade when exposed to heat, humidity, light, or air. Keep strips in their original vial with the cap tightly sealed after each use. Leaving the cap off, even briefly and repeatedly, lets in moisture that can prematurely break down the chemistry.
Store strips at room temperature, generally between 57°F and 104°F (14°C to 40°C). Don’t leave them in a hot car, a steamy bathroom, or a cold garage. Research has shown that even 15 minutes of exposure to temperatures around 107°F and high humidity can shift glucose readings by as much as 33 mg/dL, or roughly 30%. That’s enough to change a normal reading into one that looks concerning, or to mask a genuinely high result. Always check the expiration date on the vial before testing. Expired strips can give unreliable results regardless of how well they’ve been stored.
Checking Your Meter’s Accuracy
Control solution is a liquid with a known glucose concentration that you apply to a test strip instead of blood. It lets you verify that your meter and strips are working together correctly. You should run a control solution test in four situations: when you first use a new meter, when you open a new vial of test strips, if you drop or damage the meter, or if a reading seems unusually high or low and doesn’t match how you feel. Control solution is brand-specific, so use the one designed for your meter.
To run the test, apply a drop of control solution to a strip the same way you’d apply blood. The result should fall within the acceptable range printed on your test strip vial. If it doesn’t, try again with a new strip. If it still falls outside range, contact the meter manufacturer before relying on the device for further readings.
Keeping Your Meter Clean
Blood is a biohazard, and small amounts can end up on the meter’s surface, especially around the strip port. Wipe down your meter regularly according to the manufacturer’s cleaning instructions. The CDC recommends that if a meter is ever shared between people, it must be cleaned and disinfected after every single use to prevent the spread of bloodborne infections. Ideally, a glucometer should be assigned to one person and never shared. If the manufacturer doesn’t provide specific disinfection instructions, the device shouldn’t be shared at all.
Common Reasons for Unexpected Readings
If your number seems wrong, work through this checklist before assuming the meter is faulty:
- Dirty hands. Sugar residue, lotion, or food on your fingers can raise readings artificially.
- Too little blood. An undersized sample is the most common cause of error codes. Some meters will flag this; others may just give an inaccurate result.
- Expired or damaged strips. Check the date and make sure the vial has been sealed between uses.
- Temperature extremes. Testing outside on a very hot or cold day, or in a car that’s been sitting in the sun, can push readings in either direction.
- Wrong code. If you use an older meter that requires manual coding, make sure the code matches the number on your current strip vial.
- Wet hands. Water left on the skin dilutes the blood drop, potentially lowering the reading.
When in doubt, wash your hands again, use a fresh strip, and retest. If the second result is similar, the reading is likely accurate even if it’s not what you expected.