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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medically reviewed by WellAlly Editorial TeamLast reviewed October 19, 2026Editorial policy
Medical Devices17 min read

Continuous Glucose Monitor (CGM) Basics: Setup, Use, and Care

Published: October 19, 2026Updated: October 19, 2026

A continuous glucose monitor (CGM) provides real-time insights into your glucose levels, helping you make informed decisions about nutrition, activity, and medication. This guide covers how to prepare the insertion site, activate your sensor, and accurately interpret readings and trend arrows. Learn how to maintain your device properly to ensure safe and effective glucose management.

Quick Summary

A CGM automatically tracks glucose levels 24/7 through an under-the-skin sensor, alerting you to trends and high or low readings.

Important Medical Disclaimer

This guide is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with qualified healthcare providers for medical concerns.

Step-by-Step Guide

1

Select and Clean the Application Site

Choose an approved placement area based on your specific CGM model, typically the back of the upper arm or the abdomen. Wash the skin with plain soap and water, then clean the area thoroughly with an alcohol prep pad and allow it to air-dry completely. Avoid applying lotions, perfumes, or oils, as any residue will prevent the adhesive patch from sticking firmly.

Important: Do not apply the sensor over moles, scars, tattoos, stretch marks, active rashes, or within two inches of an insulin injection site.

2

Apply and Secure the Sensor

Follow your device's instructions to prepare the applicator and place it firmly against the prepared skin. Press the insertion button to deploy the small, flexible filament into the subcutaneous tissue and adhere the base patch. Smooth down the adhesive border with your finger to ensure complete contact with the skin and eliminate air bubbles.

Important: If you experience severe or persistent pain, or if bleeding does not stop after a few minutes, remove the sensor and apply light pressure with sterile gauze.

3

Attach the Transmitter and Pair Device

If your CGM uses a reusable transmitter, snap it securely into the sensor base until you hear or feel a distinct click. Open the manufacturer's smartphone application or power on your dedicated receiver. Follow the on-screen prompts to connect the device via Bluetooth and scan or manually input the unique sensor identification code.

4

Complete the Sensor Warm-Up Period

Every CGM requires an initial warm-up phase to equilibrate with your body tissues, typically lasting between 30 minutes and 2 hours depending on the brand. During this window, the device will not display real-time glucose values or sound alerts. Keep a standard fingerstick blood glucose meter accessible in case you feel symptoms of hypoglycemia or hyperglycemia during the warm-up.

5

Calibrate if Required by Your Model

Check whether your specific CGM requires fingerstick calibrations or is factory-calibrated. If calibration is needed, only test blood glucose when your levels are relatively stable—ideally before meals rather than immediately after eating or exercising. Enter the fingerstick value into your app or receiver promptly after testing.

Important: Always verify with a fingerstick meter if your symptoms do not match your CGM reading, or during times of rapid glucose fluctuation.

6

Interpret Numbers and Trend Arrows

Observe both the current numeric reading and the directional trend arrows displayed on your screen. The arrows indicate the rate and direction of glucose change, showing whether levels are steady, rising, or falling rapidly. Use these patterns alongside your healthcare provider's action plan to calculate meal boluses, treat emerging hypoglycemia, or adjust physical activity.

7

Remove the Sensor and Rotate Sites

When the sensor wear session ends (typically after 7 to 14 days), gently lift the edge of the adhesive tape and peel it off slowly. Use an adhesive remover wipe or baby oil if the patch adheres too strongly to prevent skin tears. Clean the area with mild soap, and always choose a different anatomical location for your next sensor to allow the skin to heal.

Frequently Asked Questions

Why does my CGM reading differ from a fingerstick blood glucose check?
CGMs measure glucose in interstitial fluid (the fluid between your cells), whereas traditional meters measure capillary blood. Because it takes time for glucose to move from your blood into interstitial tissue, CGM readings typically lag behind blood glucose by 5 to 15 minutes, particularly when levels are changing rapidly.
Can I shower, swim, or exercise with my CGM attached?
Yes, most CGM sensors are water-resistant and designed for daily activities, including swimming and bathing. However, check your manufacturer's depth and duration limits, and consider applying a medical adhesive overpatch if you engage in vigorous sweating or prolonged water immersion.
Do certain medications interfere with CGM accuracy?
Yes, high doses of acetaminophen (Tylenol), high-dose vitamin C (ascorbic acid), and hydroxyurea can cause false high or low readings on certain CGM models. Review your device's prescribing information and consult your doctor about your medication regimen.
What should I do if my sensor falls off before the session ends?
If a sensor detaches early, do not attempt to reinsert it, as the filament cannot be sterilely or safely replaced. Apply a fresh sensor at a new site and contact the device manufacturer's customer support line, as they often provide a replacement for premature failures.
  1. 1
    National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)Source
  2. 2
    Centers for Disease Control and Prevention (CDC)Source
  3. 3
    Mayo ClinicSource
  4. 4
    National Health Service (NHS)Source

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed October 19, 2026. · Read our editorial policy