Monitoring blood glucose means checking your sugar levels at regular intervals using a meter, a wearable sensor, or both. The method and frequency depend on whether you have type 1 or type 2 diabetes and how you manage it. Here’s what each approach involves, what the numbers mean, and how to get the most accurate readings.
Fingerstick Meters: The Standard Method
A fingerstick glucose meter is the most common starting point. You prick the side of your fingertip with a small lancet, place a drop of blood on a disposable test strip, and the meter displays your blood sugar in seconds. The devices are portable, relatively inexpensive, and available at most pharmacies.
Accuracy depends heavily on technique. Wash your hands with soap and warm water before every test, then dry them completely. Residue from food, lotion, or even hand sanitizer can throw off a reading. If you’re having trouble getting enough blood, massage or shake your hand beforehand to increase blood flow to your fingertips. Cold hands restrict circulation, so warming them up before washing can help. Rotate your pricking sites across different fingers to avoid soreness.
Continuous Glucose Monitors
A continuous glucose monitor, or CGM, is a small sensor inserted just under the skin (usually on the upper arm or abdomen) that measures glucose levels around the clock. A transmitter sends data to a paired device or phone, letting you see your levels in real time and track trends throughout the day and night.
Most sensors last 7 to 14 days before they need replacing. The Dexcom G6, for example, lasts 10 days, while the FreeStyle Libre 2 lasts 14 days. An implantable option exists as well: a small pellet about 18 millimeters long that a provider places under the skin, lasting several months. When you first apply a new sensor, expect a warm-up period of 30 minutes to two hours before it starts sharing data. Some systems also require a fingerstick calibration at startup.
One important detail: CGMs measure glucose in the fluid between your cells, not directly in your blood. Glucose reaches your bloodstream first and then moves into that surrounding fluid, creating a lag of a few minutes. This means a CGM reading can trail behind a fingerstick reading, especially when your blood sugar is rising or falling quickly. During those rapid swings, a confirmatory fingerstick can be useful.
Some CGMs connect directly to insulin pumps, creating automated delivery systems that adjust insulin based on sensor readings. This is particularly relevant for people with type 1 diabetes who need tight, real-time control.
How Often to Test
Your testing schedule depends on your diabetes type and treatment plan.
- Type 1 diabetes: Expect to test 4 to 10 times a day with a fingerstick meter, or use a CGM for continuous tracking.
- Type 2 diabetes on insulin: Testing frequency varies with the type and amount of insulin you use. If you take multiple daily injections, testing before meals and at bedtime is typical. If you use a long-acting or intermediate insulin, you may only need to check before breakfast and occasionally before dinner or at bedtime.
- Type 2 diabetes without insulin: If you manage your blood sugar with non-insulin medications, diet, and exercise, you may not need daily testing at all. Your provider will guide how often periodic checks make sense.
Target Ranges to Know
The American Diabetes Association recommends the following targets for most nonpregnant adults with diabetes:
- Before a meal: 80 to 130 mg/dL
- One to two hours after starting a meal: Less than 180 mg/dL
- A1C (a three-month average): Less than 7%, which translates to an estimated average glucose of about 154 mg/dL
These are general targets. Your provider may adjust them based on your age, how long you’ve had diabetes, and other health conditions.
What Low and High Readings Mean
A reading below 70 mg/dL is considered low blood sugar. Symptoms include shakiness, sweating, confusion, and rapid heartbeat. The standard response is to consume 15 grams of fast-acting carbohydrates (glucose tablets, juice, or regular soda), wait 15 minutes, and recheck. If you’re still below 70, repeat.
On the high end, if you’re sick and your blood sugar is 240 mg/dL or above, use an over-the-counter ketone test kit to check for ketones in your urine. High ketones alongside high blood sugar can signal a dangerous condition that needs immediate medical attention.
Substances That Skew Readings
Certain medications and supplements can interfere with sensor accuracy, producing readings that are falsely high. High doses of acetaminophen (the active ingredient in Tylenol) can inflate glucose readings on several major CGM systems, including the Dexcom G6, Dexcom G7, and Medtronic Guardian 4. High-dose vitamin C can do the same on FreeStyle Libre sensors. If you take either regularly, a confirmatory fingerstick is worth doing when your CGM reading seems off.
Tracking Your Data
A single blood sugar number tells you what’s happening right now. Patterns over days and weeks tell you what’s actually working in your management plan. Logging your readings alongside meals, activity, and medication helps you and your provider spot trends and make adjustments.
You can do this with a simple notebook, but apps make pattern recognition much easier. Platforms like mySugr and Glucose Buddy let you tag readings with context (what you ate, whether you exercised) and generate reports you can share with your care team. Glooko syncs with more than 80 devices, including insulin pumps and CGMs, and is used by many clinics for remote monitoring. If you use a Dexcom CGM, Sugarmate pulls in real-time data and can send alerts to family members. For people focused on managing carbohydrate intake, Carb Manager offers a large food database alongside glucose tracking.
Most CGM systems also come with their own companion apps that display trends, time-in-range percentages, and daily glucose graphs. These built-in tools are often enough to start identifying which meals spike your sugar, how exercise affects your levels, and whether your overnight numbers are stable.
Choosing Between a Meter and a CGM
Fingerstick meters are simple, proven, and cost less upfront. They work well for people with type 2 diabetes who only need occasional checks. The main limitation is that each test is a snapshot. You see your sugar at that exact moment but miss everything happening between checks, including overnight dips or post-meal spikes you didn’t catch.
CGMs fill that gap by providing a continuous stream of data, often with customizable alerts that warn you before your sugar gets too high or too low. They’re especially valuable for people on insulin, those with frequent low blood sugar episodes, or anyone who wants a detailed picture of how their glucose responds to food, exercise, and stress throughout the day. The tradeoff is higher cost and the need to wear a sensor on your body at all times, though most people find modern sensors small enough to forget about after the first day or two.
For many people, the two methods complement each other. A CGM handles the continuous tracking while an occasional fingerstick confirms accuracy during rapid changes or when a reading seems inconsistent with how you feel.