Continuous Glucose Monitor – How to use it effectively

February 14 13:26 2025 Print This Article

Summary 

A Continuous Glucose Monitor is a wearable technology that helps you track your glucose levels in real-time, and conveniently collates the data for analysis. It consists of a sensor and transmitter that can be connected to an app on your smart phone or smart watch for easy access. It is a useful tool to analyse the range your glucose levels go through in a 24 hour period. It can also give you insights into what causes blood sugar spikes, when combined with time-stamped data on your diet and exercise. The continuous glucose monitor is an effective tool to help you and your doctor create a detailed treatment plan and lifestyle interventions to manage your diabetes.

What is a Continuous Glucose Monitor (CGM)? 

A Continuous Glucose Monitor is a wearable technology that tracks your blood sugar levels in real-time. It is an advancement over traditional glucose monitors, which were previously used to measure blood sugar levels, typically one or twice a day. Continuous glucose monitors collect readings automatically, and sync it with your Fitbit or smart watch. This gives the wearer an easy way to identify patterns in their blood sugar spikes and drops. The data can help correlate the effects of certain foods, exercise, stress and sleep habits with the wearer’s blood sugar levels. It’s a great tool for diabetics and their doctors to get data to help tailor an individualised treatment plan to suit their metabolism. This is a space in the biomedical market which is rapidly evolving, and users can expect major improvements and innovations in CGM technology in the decade to come.

How does a Continuous Glucose Monitor work?  

Continuous Glucose Monitors work by measuring the glucose levels in the interstitial fluid under the skin. The CGM is essentially a sensor, which is placed just below the skin, allowing it to take continuous measurements and transmit the data in real time. The sensor is usually placed on the back of the arm or on the belly. The sensor has a needle, which pierces the skin to access the interstitial fluid, and is held in place by water-proof adhesive tape. The sensor can typically only be left in place for 7 to 10 days, as directed by the CGM manufacturer. The sensor has a transmitter which wirelessly transmits glucose levels measured to your smart-phone app or smart watch. Depending on the model, your CGM may measure you blood sugar at intervals of 1 to 5 mins.

Some CMGs require a “finger-prick” blood glucose reading to calibrate themselves, after which they will begin continuous measurement and data transmission. You can program alerts at certain levels on the CGM app, such as alerts for high blood sugar or low blood sugar.

Who is CGM intended for? 

CGM is primarily intended for diabetics. Patients with type 1 diabetes are prime candidates, although some patients with type 2 diabetes may also be recommended a CGM. CGM is especially beneficial to patients who:

• Are on intensive insulin therapy
• Experience hypoglycaemia (low blood sugar) unawareness. This means their blood sugar tends to drop too low without warning. This can be dangerous, and lead to fainting.
• Experience very high blood sugar levels often. The CGM has an alarm which can be programmed to alert the patient to take their medication when the levels cross a certain threshold, as directed by their attending physician.
• Are introduced to a new medication or treatment method, to monitor its effectiveness.
• Are suffering from gestational diabetes (diabetes during pregnancy)
• Pre-diabetics, and others at a high risk of developing diabetes

Although it is widely accessible, CGM is not recommended for non-diabetics.

How is CGM beneficial?

CGMs are a life-changing technology for diabetics. They can:

• Offer useful insights into the patient’s health – CGM allows you to track your levels, and analyse the trends on a graph to a reasonably accurate degree. It allows you to track your blood sugar levels even while you are asleep. The CGM, most importantly, gives your health-care provider a good sense of how your blood sugar levels are affected by different foods, exercise, stress, hormonal changes and sleep. The CGM also helps keep a check on the effectiveness of the diabetes medication prescribed to you.
• Alert you to dangerously high or low glucose levels – With diabetes, taking action at the right time can be crucial to prevent a host of complications, such as permanent damage to eyes, nerves and feet or diabetic ketoacidosis.
• Help make informed decisions – Access to detailed blood sugar data can help you and your doctor make informed decisions about your health. The warnings help you take action at the correct time, and avoid dangerous highs and lows in your blood sugar. The data can also help your doctor arrive at the correct dosage of insulin.
• Offer peace of mind – Having access to continuous data can ease patients’ anxiety around high glucose levels, and give the patient confidence and certainty that their medication is working.
• Better long-term outcomes – Understanding the effects of the patient’s lifestyle on their blood sugar levels can help evolve better long-term strategies for diabetes management.

What are the limitations of CGM?  

As revolutionary as the technology is, CGM does come with some limitations that must be understood when using the data to create strategies for diabetes management. The CGM measures the glucose levels in the interstitial fluid below the skin and not in your blood itself. Although this is a fairly good indicator of the upward and downward trends of your blood glucose levels, glucose takes some time to travel into the interstitial fluid from the blood. Another important thing to remember is that most companies recommend verifying CGM values with finger-prick glucose tests periodically, to verify measurements. So, although CGM reduces the frequency of finger-prick glucose tests, it does not eliminate them entirely.

Some patients also find the CGM sensor to be a little uncomfortable to wear, and tend to keep knocking the device against things, potentially damaging the sensor. If the CGM sensor falls off before it is due to be removed, for whatever reason, it cannot be re-inserted, and the patient must get a new sensor. It is also important to note that you cannot wear a CGM during X-rays or MRI scans as the radiation will damage the device or cause malfunction. Certain medications such as vitamin C (ascorbic acid), acetaminophen or hydroxyurea can affect CGM readings as well.

Understanding your CGM data 

Your Continuous Glucose Monitor provides you with a LOT of data, and this can be overwhelming for someone using it for the first time. We recommend beginning with 2 major data points:

• CGM glucose range – This would be the range within your blood sugar fluctuates, within a 24 hour time period. This would usually tell you when your blood sugar is highest, when it is lowest, and whether it is within a healthy range. If your blood sugar is found to fluctuate outside of a healthy range, your doctor can help you put strategies in place to correct that, or at least explain what emergency protocols to follow when it gets too high or too low.
• CGM glucose trend – Most CGM apps have a “trend arrow” which indicates whether your glucose levels are falling or are on the rise. The trend arrow is helpful in warning you about what could happen, so you can be prepared to take action. For example, if your trend arrow indicates that your blood sugar is increasing, while your levels are already on the higher end of your ideal range, that’s a warning to take action to prevent hypoglycaemia. Trend arrows also help with pre-meal insulin dosing. Trend arrows can also help understand the effects of different foods and activities on your glucose levels. If you find that your glucose levels are spiking after a meal, taking a walk immediately after can help bring that spike back down.

After a few days of collecting data, larger trends may begin to emerge. To make the most of this data, you will also need to log your food intake and exercise accurately with time stamps. We always recommend decoding this data with your doctor, and not trying to do this on your own. The CGM can help you determine how much time your glucose levels are in the healthy range, and when the spikes happen. The ultimate goal is to alter your lifestyle and diet in such a way that you spend as much time in the healthy range as you can. For most diabetics, spending at least 70% of their day within the healthy range is considered good.

Tips to use CGM more effectively

1. Set slightly lower glucose levels on the CGM – Since the CGM measures glucose levels in the interstitial fluid, which is usually a little lower than blood glucose levels, it is recommended to set slightly lower values for the highest and lowest levels in your range. For example, the currently accepted blood glucose value for after a meal is at 140 dl/L. Since the CGM measures glucose levels in the interstitial fluid, you could set your alert at about 110 to 120 dl/L. These decisions must be made in consultation with your doctor.
2. Don’t become obsessive – Having all this data at your fingertips can be overwhelming, and patients tend to become quite obsessive about checking their levels constantly. It is very difficult, even for non-diabetics, to keep their blood sugar within the optimal range AT ALL TIMES. As long as you are within the optimal range about 70% of the time, you are good. Set your alerts for the highest and lowest values of your healthy range in consultation with your doctor, and don’t think about it unless the alarms go off. Sometimes, the stress caused by constantly checking your CGM can do more harm.
3. Use the CGM for accountability – Your CGM gives you a lot of information on what spikes your blood sugar, and what can bring it back down. Learn from this, and incorporate it into your lifestyle. Use your CGM to track your progress, and be honest with yourself about what’s working and what isn’t. Use it to convince yourself of how you need to live.
4. Take CGM calibration seriously – CGM calibration needs to be accurate to make sure the data you’re getting from your CGM is indicative of your actual blood sugar levels. Make sure you wash your hands well before you take the finger-prick test. Try not to calibrate your CGM when your glucose levels are low or rapidly changing, as this can also affect readings. Verify your CGM readings with finger-prick tests for the first 2-3 days to make sure it’s actually working and calibrated correctly.

For personalized diabetes care and management, consult the specialists at Kauvery Hospital. With branches in Chennai, Hosur, Salem, Tirunelveli, and Trichy, our experienced team is dedicated to helping you optimize your health with the latest advancements in diabetes technology, including Continuous Glucose Monitors.

Frequently Asked Questions

What is a Continuous Glucose Monitor (CGM)?
A CGM is a wearable device that continuously tracks your blood sugar levels in real-time, sending data to your smartphone or smartwatch.

How does a CGM work?
It uses a sensor inserted under the skin to measure glucose in the interstitial fluid and wirelessly transmits readings at regular intervals.

Who can benefit from using a CGM?
CGMs are especially helpful for diabetics, including those on intensive insulin therapy, patients with hypoglycemia unawareness, and those with gestational diabetes.

What are the benefits of using a CGM?
A CGM provides continuous data, alerts for high or low glucose levels, helps analyze trends, and supports informed decisions for diabetes management.

What are the limitations of a CGM?
CGMs measure interstitial fluid (not direct blood levels), may require periodic finger-prick tests for calibration, and the sensor can be prone to dislodgement or interference from certain medications.

What tips can help me use CGM more effectively?
Set personalized alert thresholds with your doctor, avoid obsessively checking readings, calibrate the device carefully, and use the data to guide lifestyle and dietary changes.

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai (Alwarpet & Vadapalani), Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

Chennai Alwarpet – 044 4000 6000 •  Chennai Vadapalani – 044 4000 6000 • Trichy – Cantonment – 0431 4077777 • Trichy – Heartcity – 0431 4003500 • Trichy – Tennur – 0431 4022555 • Hosur – 04344 272727 • Salem – 0427 2677777 • Tirunelveli – 0462 4006000 • Bengaluru – 080 6801 6801