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CGM tips and tricks

I have been using CGM for over 5 years and have been prescribing it for just as long. I’ve seen the technology's high points and limitations. Though it isn’t perfect, IT IS the best thing to happen to PWD in the last 50 plus years. Even so, I often hear frustrations from patients regarding CGM accuracy, alarm fatigue, and adhesive issues. I wanted to share some of the things I’ve learned.


This is where I get the most complaints. Remember, CGM and blood glucose meters are measuring different things. BG readings are taken from blood and CGM readings are taken from subcutaneous fluid. A small margin of error is to be expected. If there are large discrepancies between the two, wash hands, and repeat the test. I often find that my blood glucose readings are more accurate after hand washing.

CGM will be most accurate during times of stable glucose, such as while fasting or before meals. This is therefore the best time to calibrate (if needed). Calibrating during rapid changes can lead to further CGM inaccuracies. I NEVER recommend calibrating after meals, exercise, or a bolus of rapid acting insulin. Why? Because CGM will not be accurate during these times. I repeat….tight accuracy is not expected. CGM readings will always lag behind blood glucose readings during rapid rates of change. In my opinion, this is most important to account for during correction of hypoglycemia. Take last night for example; after dinner I was alerted of a postprandial low in the 60’s. I corrected it with two glucose tablets (8g total). After 15 minutes, my CGM still read <70mg/dL, however instead of taking more glucose, I tested my blood sugar using my meter. My meter readings showed a BG of 93mg/dL. Had I corrected my CGM “low” again, I would have overcorrected and eventually become hyperglycemic. Because I knew about the lag time I did a fingerstick, was confident that my glucose had normalized, and then simply waited for my CGM to catch up (which it quickly did).

CGM becomes more accurate for the longer it’s worn. It is therefore the least accurate on day one. Some PWD, myself included, use a technique referred to as “sensor soaking”. This means inserting the new sensor 3-12 hours before the previous sensors end. This means the PWD is still wearing and getting data from their old sensor while also wearing their new sensor without the connected transmitter. Though it requires wearing two sensors for the day, many PWD swear by it.


Remember, CGM is meant to be a teammate, not a nuisance. Many people don’t realize how often their glucose fluctuates until they begin using CGM. Just because a CGM offers multiple types of alarms, it doesn’t mean they should all be used at once. I typically recommend conservative start settings, such as a low alert of 70 mg/dL and a high alert of 250 mg/dL then tightening them over time.

Close attention to trend arrows while using CGM is key! For instance, a CGM reading of 100 mg/dL with one arrow down means my glucose will likely hit 70 mg/dL within 20-30 minutes. Taking a small amount of glucose will likely help me prevent my low alert from ever alarming.


If the sensor adhesive peels right off of your body, try using extra tape. I like griff grips. If allergic reactions are common, prescribed barrier wipes can be effective, however I’ve found that coating the skin with over the counter flonase before insertion works just as well if not better.

Ultimately, CGM is an incredible tool when appropriate expectations have been set. I love my CGM and I hope some of these tips can help all you diabetes “robots” love yours just as much.

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