I know 20% is an acceptable difference between cgm readings and real blood sugar #. Can you tell me what that translates to in actual points? My cgm is sometimes 30 pts off is that acceptable or too much.
Thanks so much
Lori
I am not sure I understand the question.
The number of mg/dl (for example) that a 20% difference would equate to of course depends on what the reading is.
If your meter BG is 200 then 20% is 40 points or a SG (Sensor Glucose) value between 160 and 240.
If you meter BG is 150 then 20% is 30 points or between 120 and 180.
If it is 100 then 20% is 20 points.
No?
Well according to Joslin and regarding the CGM, the finger stick is the most accurate reading for a bg. They say:
The CGM “Can tell if blood glucose is rising or falling, indicating a possible need to treat”
“Doesn’t replace the finger stick: you still need to do a meter reading for accuracy”
The CGM is not a right now reading, so if you want that then you need to use your meter. What is acceptable is for you to decide.
I was just trying to determine if the cgm was very close to my real blood sugar. I understand is should be different sometimes it seems like the difference is really off.
Thanks Lori
Which CGM are you using?
When blood sugar is rising or dropping, CGM readings tend to lag behind, but do usually catch up.
To find 20% of a number, just multiply it by 0.2. So if you’re reading is 100, then 100 * 0.20 = 20 points is 20%. If your reading is 50, then 50 * 0.2 = 10 points is 20%. If your reading is 250, then 250 * 0.2 = 50 points is 20%.
So how many points 20% is changes depending on what your blood sugar is at the moment.
BTW, i found that having the sensor on different parts of my body got me different results. my abdomen, which is what dexcom approves as the “right” site, gave me the worst possible accuracy. when i switched to my thigh, my accuracy became in line.
also, remember that your meter is not going to read 100% accurately either. you can test 5 times one after another and get 5 different results. different meters have their own different accuracy results.
I totally agree with @Daisy_Mae. I use the Enlite by medtronic and I find that the lower back (upper buttocks area, slightly above the hips) works fantastic. I’m usually on target with very little deviation. I was say 10pts +/- I would say in 6 days it gives me, I have a couple 2-3 deviations but in all the sensors are really reliable. I would also say, if you have the Enlite, Calibrate a lot! I think the recommened threshold for calibrations a day is 6 or more.
Busybee
No, it is 3.
Hi @phoenixbound,
you are right its 3-4 documented but in my training, the medtronic local rep mentioned numerous times that calibrating 6 or times a day gets better results. I usually don’t have issues with my sensor. The rep said that they have found 6 or more times of calibration a day helps the transmitter/sensor to perform better in their experience and feedback from customers.
Busybee
For those of you using the Dexcom CGM, please be aware that MORE is not BETTER when it comes to calibrating. Twice daily and only when the directional arrow is horizontal leads to the highest accuracy. Over-calibrating leads to less accuracy for the majority of people.
Your reps suggestion to calibrate 6 times a day is counter to EVERY SINGLE hard and fast rule laid down by no less than 10 of MM’s reps and tech support people. I’ve talked with countless MM techs about sensors and I can assure you that they ALL have said not to calibrate more than 3 times a day. Emphatically, to the point of reprimanding me if I mentioned to them that I calibrated more often on days when I had a flaky sensor. You will not get good results by confusing the CGM’s algorithm with too many calibrations. Shame on your rep for giving you such bad advice. My sensors or often within 2 points of my meter. Are you getting that kind of accuracy?
Wow, yes I remember with the older sensor model the practice was little is more with calibrations but then with the new Enlite the rep said to calibrate more but not on upswings, downswings, and big spreads. I’ve never really had any issues with my sensors. My BG and sensor are usually spot on each other. The biggest spread I usually have is 10pts +-. Accuracy and reliability is high for me. Good to know though.
Thanks for the feedback.
Busybee
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again, the rep is absolutely wrong in claiming an Enlite needs more calibrations than the sof sensors. If you doubt me, just call tech support and see how they react to your telling them that a rep told you to do 6 cals a day. 
I don’t doubt your feedback, I do believe you. I was slightly concerned that I might be in the wrong, so I did call medtronic. The rep said that 3-4 times a day calibration is for best performance but I explained her to my situation. She said that calibrating more than 4 times day isn’t a bad thing, she said that really you can calibrate more if calibration occurs during appropriate times- when no arrows are displayed on sensor reading, before meals, and when BG is stable (ie not during or after meals or during highs). She said that’s why I get good results, i calibrate at proper times. There is a minimum amount of times to calibrate to set up the sensor in order to work properly but if calibrations are conducted at the right time, then they can be performed more than 3-4 times a day. Below is the info from www.medtronicdiabetes.com on calibration and when to do it.
How to Calibrate
Important: Calibration is important for sensor
performance. Calibrating 3-4 times per day can optimize sensor
performance. Wait at least 10-15 minutes between calibration entries.
To calibrate, you must use a fingerstick blood sample to test your BG
on your meter and then enter that value into your pump. The pump will
accept BG meter readings between 40 mg/dL to 400 mg/dL. And the minimum
number of calibrations required is once every 12 hours (after the first
day), but calibrating three to four times a day can optimize sensor
accuracy.
Best Times to Calibrate the Enlite Sensor
Calibrate three to four times spread out throughout the day.
You can calibrate anytime during any rate of change. However,
calibrating with two down arrows or two up arrows may decrease accuracy
until the next calibration.
Before bedtime
Before insulin
Enter your meter BG reading into the pump immediately after testing your BG. Do not wait to enter it later.
Busybee
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If u calibrate twice in 10 minutes only the second calibration is utilized. You will eventually learn what works