Dexcom G6 CGM accuracy causing health issues!

Issues with Dexcom G6 CGM * Accuracy causing **


I’ve had issues with both the G5 * G6 (but far worse with G6) where readings may match fingers tick on one day and literally be 50 to 100 points off the next. Today the CGM read 65 (slightly low, but nothing to worry about) and when I started seeing (or not seeing) things clearly I took a finger-stick - read 35!! [I’ve been even lower and not felt anything].

All Dexcom says is recalibrate. When I tell them they advertise no finger-sticks needed, no calibration needed (and therefore test strips not covered) they essentially tell me out of their pay grade.

If anyone else having similar issues would like to know. Would be great to set up a simple test of CGM accuracy for those who still have finger-sticks (maybe test twice a day when no up or down or angle arrows plus anythme blood sugar out of range (and arrows flat)??

ONLY if enough of us make some noise as a group will things change!!

I’m happy with G6 and have no issues. Not discounting your issue, just a lot of times on the forums you only hear from people having problems.

Dexcom has acknowledged there are some groups that use G6 and have issues: those with a low BMI and certain children. Not sure if they have made progress on that issue or if those learnings will be used to advance G7.

Then there are also all the other issues like compression lows, those who soak vs those who don’t soak sensors, and a big one especially with old timers is that they are often using old meters with a low MARD rating or not properly preparing finger for most accurate finger stick results. Both CGM and glucose monitors operate within tolerances and limits which can be near or exceeded by individual so there are just way too many variables for a comparative test.

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How many shipments of G6 have you had? I think people occasionally get a bad shipment. The first shipment I received, everything irregularly read 50 - 100 points off. I haven’t had that much difficulty since.

You must call them and have the sensor replaced when it is that far off the mark. Thats the only way to make them aware/accountable for failures. 20% - 25% error is when you report the sensor. If you are 25 points off, call it in.

If you are seeing error like that, then you MUST be verifying with fingersticks. You must. Otherwise, you are walking a fine line of a dangerous situation. You might need to check 4 x per day. You might need to check 8 or 10 times.

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I am so sorry but I am one of the very lucky ones! I haven’t tested in so long, I think I will have test strips that will expire. I don’t know how accurate the sensor is because I don’t test. I just let the system do its thing. I have had no problems at all.
While doing clinical trials, I have compared the Dexcom to lab numbers and all the different meters. My Dexcom is always right on. Not exactly the same number but close enough for me. Some people also check their blood sugar whenever the go to have lab work.
I know there are people who, this system doesn’t work well. Body chemistry, body weight etc makes some to be not a good fit. I do sometimes have issues if the sensor is in a less fat part of my body(not many of those🙁).
I guess you might be one of those people who it doesn’t work as well. But if it was me, I would be on the phone every time things were not working.
I did have one box with the same Lot # that dropped out a lot. Called during each one and it wasn’t until the three one, that I finally put it together that it might have been the Lot #. I just don’t have issues and since a new box, no problems.
So sorry, things are not working for you. This is how I felt when working with Minimed’s first CGM sensors. I hope you can find some answers!


I have been on G6 since release. I use G6 to drive my Tandem CIQ pump. I have compared my G6 to hospital lab values. The hospital lab values were consistently lower than the G6 because red cells eat sugar out of the blood between the time the blood is drawn and when it is spun & separates for testing of the plasma sugar. The difference was always 12 points. The comparison was done when I was hospitalized for 6 days made 4 comparisons.

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Not even close to good enough for government work!! It was done with 1 patient a limited number of sensors and a setting far different from real life.

You missed the point. Folks were discussing their concerns. My experience during hospitalization with daily blood glucose draws demonstrated to my satisfaction the G6 meets the gold standard. Review the entire thread. Mine was one patient, one sensor, and good enough for insulin dosing by Tandem CIQ pump in an ICU.

The point of the original post wasn’t personal - it was certain people (self included) that the system doesn’t work for sometimes -> I know lots of people it works for beautifully, some that it never does and a good number it works sometimes and fails others. Question is identifying why (and no, not technique, I worked on these devices at one time, understand where/how/when to do a new CGM insertion too well)

I have never trusted the G6 or finger sticks for actual readings… I tend to use the G6 for trend information.
Nor have I trusted the no calibration, l look at it as if it didn’t need celebration, it wouldn’t in the menu. I also have a tendency to calibrate at least four times a day.
If the finger stick is way out of line 40-60 points I will do another finger stick. I’ve also have noticed I can get various reading from hand to hand finger to finger. Appears all of us have varying issues with the G6 of one sort or another.

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@Yerachmiel here is something I picked up on a post in another D forum about CGM, FS, & Calibrations

CGM Calibration Facts & rationale to avoid pitfalls & rabbit holes

NOTE: The term “rabbit hole” comes from the 1865 piece “Alice’s Adventures in Wonderland” by Lewis Carrol 1865 and has come to mean a bizarre, confusing, or nonsensical situation or environment, from which it is difficult to extricate oneself.
Test by finger stick (FS) anytime CGM doesn’t seem to match the way you feel.

Learn & verify acceptable deviation according to FDA approvals, ±20% above 100mg/dL and ±20mg/dL below 100. Examples, CGM =200, then FS can be between 160 & 240 and still be fine, or CGM = 70, then FS should be between 50 & 90 with level CGM.

Wait 60 minutes between tests if testing for CGM for validation.

Remember, CGM measurements are interstitial fluid and finger sticks are whole blood.

Whole blood & interstitial fluid are physiologically different & 15-20 minutes apart in the movement of glucose.

Call tech support if 2 tests are >20% off, 1 hour apart. You may need a new sensor or have other technical issues.

Only enter calibration when tech support instructs. This reduces the number of times you will get into the calibrate, calibrate, calibrate rabbit hole.

If you are calling tech support for a goofy sensor, request replacement, regardless.

Follow tech support about changing a sensor.

Avoid the calibration rabbit hole of the system requesting multiple calibrations for hours and sometimes days.

Not everyone (some doctors) who prescribed insulin fully understands CIQ & how it uses CGM.

Why FSs & CGMs don’t play nice together.

First, FS & CGM are only expected to be within 20% of each other according to published standards accepted in the USA by the FDA. If your CGM says 200 then ±20% is ±40 mg/dL meaning a finger stick is fine if it is between 160 & 240. At the same time if CGM says 100 the ±20% would be 80 to 120. BELOW 80 it is ±20 points (mg/dL) without the percentage according to US FDA standards.

NOTE: Some individuals expect much narrower values between FS & CGM, even to the point of expecting them to match spot on.

Second, as food is eaten, the food enters the blood stream in various places along the digestive tract. Some enters quickly from the mouth, like granular sugar placed under the tongue. Other foods swallowed quickly may not enter the blood stream until arriving in the stomach. The final absorption occurs in the small intestine.

After food is absorbed into the blood stream, it is ‘checked’ by the liver and then dispatched thru the body in the blood stream.

After glucose is in the blood stream, the glucose moves in the liquid part of the blood (sometimes referred to correctly as plasma or serum - like serum or plasma glucose for the doc’s office or hospital blood test) into the interstitial fluid that moves around all body cells outside the blood vessels. It is this interstitial fluid that CGM sensor wires are in to read the glucose and report it to our measuring devices.

The time for all of the glucose movement to take place is usually 15-30 minutes or more, depending on multiple variables including the amount of carbohydrates, proteins, & fats in the consumed food which changes the way the food is processed in the body.

It is this 15–30-minute interval and body fluid differences that give significant part to the variation in CGM and FS readings. This is also the reason most comparisons are done when glucose values are demonstrated level by the CGM before doing comparison finger sticks.

Wish they would play nice together……

Just for note, I have been using G6 since it came out. I have been using Dexcom for 20+ years. With G6, I have not needed to do a finger stick for more than 18 months.

I can report while hospitalized in Jan 2020, I had chemistries drawn every morning for 5 days straight. The difference between the hospital lab and the G6 was less half of the allowed difference between a finger poke and the CGM allowance. It was always 14mg/dL. Even the hospital laboratory supervising pathologist got in on the ‘game’ before the end. Are you expecting something outside of parameters or is there a need to RTM instead of SOTP. Thoughts?