The Dangers of CGM's

So I have had a minimed CGM in the past few days and I realized that it can actually pose a threat to me. The CGM gets it's readings from the interstitial fluid between cells, which isn't the same as blood sugar concentration, but it tends to mimic it. The danger comes when there is a varying lag between when the blood sugar concentration changes and when the interstitial fluid sugar concentration changes. For example, the previous CGM's I've used have lagged 5 minutes between when they tell me my blood sugar is going low and when it actually is going low. I deal with this by checking if there is a trend of my blood sugar dropping in the last few minutes and set my low alarm to 4.2 mmol (76 mg/dl). However, the cgm I'm using now seems to lag from 10-15 minutes behind, so I can feel a bit low, but look at my cgm and it says my bs is stable at 7.0 mmol (126 dg/ml). As a result, I've gone very hypoglycemic without realizing I should check my meter and then correcting with carbs. Does anyone else have this issue and/or have any suggestions of how to deal with it? 

You might want to set your LOW warnings a bit higher, so that it alarms before you get so low. 

in the beginning of starting to use the CGMS, it takes a LOT of time to learn the tricks to get it to perform

at it's best.

Remember to calibrate when your blood sugars are stable, that will give you te best results in what

you see on the readout.  I've been on the MM CGMS for about a year now, and still have to fiddle with

the settings from time to time.

You are correct that there is a lag time, so if you feel low, test you BG and treat it.  We tend to get lazy

when we go on CGMS and rely on it too much and make decisions based on what it says.....that can be a

big problem.  I find it just can't keep up with my actual BGs...but it does give me trending information.

Hi, Mine does this too sometimes. Sometimes it is very accurate and at other times (like you said) it can be almost 20 points off. I asked my doctor about this. He said this can happen because the sugar readings are more accurate in the blood because the interstitial fluid is always a little delayed. Im not really sure how to explain it. But really you should just listen to your body. If you feel like its low but the CGMS says its not, then definitely check your sugar with your meter.


The CGMS is a great function and very good at detecting trends and can also serve as a warning sign for highs and lows. As you pointed out, it is not always 100% percent accurate when it comes to certain things. When a rapid change in glucose is happening as of yet it cannot keep up with the changes that accurately. It kinda stinks that way, but one day maybe it will.

The thing is that one can never rely on the CGMS to replace testing as of right now. I mean if it is calibrated appropriately it will work wonders and generally can be very close to letting you know what is going on. However, as stated above if you feel the symptoms of a low than generally your body is probably closer to being right, than the CGMS. I love my CGMS system and it has changed my life in leaps and bounds, but I knew from the beginning that I could not allow it to replace testing and such. Would I give it up?? Not without a chance, but there are some hazards as you pointed out. As long as you realize this though, you will be fine and learn how best to integrate the CGMS into your life or maybe decide that as of right now it is not for you.