# What is your Glucose Standard Deviation?

I am very familiar with A1C numbers and I know what A1C I would like to see for myself. However, I feel that going after a certain A1C number is putting the cart before the horse. First I need to learn how to keep my bg in a narrow range and then I can choose an appropriate mean glucose level. What is your glucose standard deviation and what mean glucose level goes with it?

Hello Helmut. My current BG average is in the lower 90’s and my standard deviation fot the past seven days is 21. During that week I had three tests in the 50’s several in the 60’s, and I also had highs of 167, 144, 140 and 132. My comfort range is 70-130.

The stsndard deviation for a diabetic who tests only a few times per day is of very little value. For a good estimate of your true standard deviation you need a lot of tests throughout the 24 hour period. I test 12 times per day, including twice during the night, so my standard deviation is a reasonably good estimate.

Some pumps will give your average and standard deviation for any period of time. Mine does not do that so I have to use my calculator. It has a statistical mode.

I have a friend whose average is 90 and standard deviation is 13. That is ideal!!!

Richard, 21 is remarkable. My DexCom software shows SD=32 and Mean=99 for the last 3 month. Did you get your Dex yet? It would be interesting to compare the finger stick SD with the DexCom SD. Is your friend a T2? I cannot imagine a T1 with SD=13.

This is a great question, and I love seeing people really looking at the wealth of data that the Dexcom software provides to help them aggressively manage. My feeling is that, if you’re using the Dexcom system, calculating a standard deviation using your fingerstick readings is kind of irrelevant. I still do 7-10 fingerstick tests a day, but those are cherry-picked results; roughly half of my fingerstick tests are 2-hour postprandials, but the gross amount of time I spent having just eaten is (obviously) considerably less. Then you add in the number of fingersticks I do when I’m feeling “off,” and the fingersticks are likely to be weighed toward time I’m out of range.

My mean is 99, with a standard deviation of 22, showing I’m in target 88% of the time. My target range is the same as Richard’s, 70-130. 7% “high” (130-240), 4% “low” (55-70). My last A1c was 4.9%.

Now, I’m happy with my A1c, but it has to be taken with a grain of salt. As it’s been explained to me, the A1c represents an average. The average of 90 and 110 is the same as the average of 50 and 150, or 25 and 175. That in mind, I actually consider the CGM readings to be a better indicator of my health than the A1c.

Andrew, thanks for sharing your stats. Your numbers are exactly what I am shooting for. My target range is 70-130, influenced by the scale of the DexCom glucose distribution graph. I am only 70% in target, 15% low and 15% high. I was on conventional insulin therapy during that time. This week I got an OmniPod. Time will tell whether this gadget will save the day.

Dex has not arrived but it should be here before New Year’s Day. My friend is Type 2 and a member of this site. His name is Lloyd and he is still pumping with a Cozmo and using his Navigator CGM. He started the Navigator user’s group here.

My standard deviation for the last month is 43 with an average of 119. I use the Dexcom CGM and have been following the “Success Chart” rather closely. I started on the Dex on September 4 and I have watched these statistics steadily improve in the week over week and month over month comparisons.

My current goal is a standard deviation of 30 with a mean of 110. Once I get there then maybe I can dream of the numbers that others here report. I’m thinking that I’ll need to reduce my carb intake to achieve that.

One step at a time. The Dex is awesome!

Helmut – good luck with the OmniPod. With your attention to detail I sure you will find pumping a liberating experience.