G6 Blood Glucose readings lag 15 minutes behind blood testers

I had been noticing my Dexcom G6 sensor readings to my iPhone are lagging what my OneTouch Verio Flex meter tests them as. My present Dexcom sensor went into a mode where I was requested to calibrate the App daily and I am noticing how different the readings regularly are. So I called Dexcom and the person calmly said that the Dexom meter readings nearly always lag by 15 minutes and could be as much as 30% off, depending on how high or low your BG is.
I’m wondering about others experience and looking for a discussion about ways to factor this in to my insulin regimen.
I am experiencing some pretty big swings because I am over reacting with too little food/glucose tabs for lows AND too much insulin for highs.
Looking forward to your insights!

Yes, interstitial fluid reading always lags finger tests by about 15 minutes. You never want to do corrections or calibrations while BG is either climbing or descending. Dexcom reads out every 5 minutes so you want to make sure that you have 3 horizontal dots (1 dot = 5 minutes) before making adjustments. Otherwise, you will just be chasing the reading and be on a permanent roller coaster of highs and lows. You also want to have measured snacks such as candies. I use Swedish Fish candies as each one I consume raises my blood sugar exactly 10 points. So if my horizontal readings are 30 points lower than I would like to see them, I eat 3 Swedish fish and within 1 hour my horizontal readings will have risen 30 points, all while staying horizontal. That is how I micromanage my BG.


Can you provide a picture or description of what you mean by “make sure that you have 3 horizontal dots (1 dot = 5 minutes) before making adjustments.”
Thanks for taking the time to guide me.

Description is best as I have not had to make adjustments using candy for lows or insulin for highs in past several days. I use the Dexcom receiver. The Dexcom guides tell you not to calibrate or make adjustments when the trend arrow is rising or falling. Only make adjustments when the trend arrow is horizontal. Even more important is that the trend arrow needs to be horizontal for 3 dots which equals a 15 minute time-frame. This is the approximate time it takes a snack to start registering on the Dexcom even though a finger stick will register faster. This is for low events.

For high events, I take 1 unit of fast acting Humalog for every 20 units of BG I want to drop. Once this is done, I make no further fast acting insulin insulin adjustments for a 2 hour period, otherwise my insulin stacks and causes excessive quick drop followed by low event. I reached these formulas through extensive testing over the years and find they work perfectly for me and for many others, while some individuals need a more aggressive approach, while others need to be less aggressive which is why YDMV.

This is an old article. The acetaminophen issue is less of a concern with the G6. It’s still fairly helpful information, though.

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Robyn, thanks for that article. Both you and CJ have given me great new practices to put into place.
I will not calibrate when my BG is moving up or down
I will be more patient to let my BG rise or fall according to glucose tabs or the insulin I have taken.
I may try this trick too: “wear two sensors at one time – the current one that is still running and giving me data, and the new one that is inserted into the body but not connected to the transmitter. When the previous CGM expires, I simply put the transmitter on the new one and then start the official two-hour warm-up.”

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I’m using my iPhone 6S as my receiver so I never see the 3 dots. I do, however, see when it’s horizontal. I just got my G6 yesterday so I’m still learning. I use Lantus and an InPen to keep my BG in check. I’m trying to stay off the pump for a while if the endo will let me with this new set up. I don’t see her again until July 7th. So we’ll see how well my readings are now that I have the G6. It alerted me last night to a low, so I’m still trying to learn what affects me and by how much because I ate a yogurt last night and over corrected. I’m getting frustrated with learning all of this.

EGreen, be encouraged! We have all had that learning curve and are continually improving.

Know that some days you just don’t know why your BG is acting strange. Other days you can identify it easily. (snacking or stress does it to me.)

Thursday I could not get my BG down no matter what I did but I had to keep eating low carbs.

Friday, I could not get my BG to stay much above 110 and I was eating most of same things with similar morning insulin doses.

The G6 helps to alert us but I am finding that it is too easy to over react. That’s why waiting for 15-30 minutes before dosing again or eating a snack is the discipline we must master.

Thank you for the encouragement! I’ve been on the Freestyle Libre for a month now. I’d used it before and it was the only thing my other insurance would pay for as far as CGMs were concerned, so I didn’t have the alert. For the most part today 70% I was in range. It’s getting better!

RLS1. You hit it on the head. It is extremely important for us not to over or under react to any meter reading.
I personally find it had to understand why if I eat the same thing every morning and take the same amount of navalog.
That by mid morning I could be steady or going low.
We all have to be aware that there can be difference between a finger stick and a CGM reading.
I’ve been on a CGM for several years now and it’s taken awhile to realize it just one of many tools for us to monitor ourselves.