Thoughts after using a CGM for a Week

Thoughts after using a CGM for a Week

It has been over one week of using my “toy” (a Constant Glucose Monitor) and I am still just as much in love with it as I was that first day. This CGM has given me invaluable insight into what my body is doing. I can actually see the glucose / cortisol relationship with real numbers! I plan on continuing to publish my findings on this blog so that others can apply them in their own life (with the support of their own medical team).

glucose monitor
I know I probably should not refer to prescription medical devices as toys, but to my engineering heart this is absolutely one of the best gifts I have ever received!

I am also in awe of the improvement in the technology. Keep in mind that this isn’t the first time I have had to test my blood glucose. When we thought I had hypoglycemia, I would regularly test my sugars in the mid to late 90’s. Those finger pricks required so much blood! Nor is this the first time I have used a Constant Glucose Monitor. In 2005, I was hooked up to a massive brick in order to help determine if this was true hypoglycemia or if it was another medical condition (Spoiler: It was Addison’s Disease).

Constant Glucose Monitor
On the left is a picture of my original CGM from 2005. On the right is my current CGM.

But while I am over here singing the praises of this CGM, I must also make note of some of the limitations. Below are three things that I have noticed after wearing my Constant Glucose Monitor for a little over one week.

1. The CGM Measures Something Different than Blood Glucose

Glucose Explanation
This was found in the “getting started” section of my Constant Glucose Monitor.

It is important to note that what I am measuring with my CGM is different than what I am measuring with a finger stick test. Both tests are measuring glucose and both provide valuable information. However, you need to know that each test works a little bit different. Blood glucose will lead the sensor glucose. I have noticed that there seems to be about a 45 – 60 minute delay between when I eat and when I see the results on my sensor readings. You can think about cars on a train in order to help visualize this relationship.

In our world, this is very similar to saliva cortisol readings compared to blood cortisol readings. Both tests provide useful information, if you know how to interpret them. Saliva is more similar to the sensor glucose readings, while a blood cortisol draw would be more similar to a finger prick blood glucose reading. This is a very simple explanation of a complex topic, but on the base level, it works.

2. Expect Variation in the Glucose Numbers

Glucose Readings
It is important to note that there will be variations in the readings.

This is a continuation of the previous observation. That first Saturday on my CGM, I realized I was reading several abnormally low glucose readings. For those of you neither hypoglycemic nor diabetic, ideally your glucose should remain above 60. And yet, here I was at 44. Logic says I should have been passed out or extremely lathargic. I had eaten food at 12:30pm, but yet my CGM was still flagging me as critically low at 1:15pm.

I did not feel low, so I decided to test my blood glucose with a finger prick. It read 100. There is quite a bit of difference between a glucose reading of 44 and a glucose reading of 100. What number should I trust? I realized that my finger prick set-up came with a control liquid in order to calibrate the test strips and get confidence in accuracy of the numbers. Put a pink drop of liquid on a test strip, and the reading should come back between 110 – 137. Perfect. Let me try that.

glucose control reading
This was suppose to read between 110 – 137. It read 143, which was high. This means all readings from my finger prick are actually high.

My finger prick control came back at 142 mg/dL. That is outside of the expected control range. This meant that my blood glucose was probably not 44. Nor was it probably 100. It was somewhere in between, with the exact number being impossible to determine. Lovely.

3. Data Requires a Sanity Check

glucose trends
A constant glucose monitor is very helpful in showing trends over time.

With this Constant Glucose Monitor, I am not looking for absolute numbers. If I was looking for absolute numbers, I would have freaked out with my glucose reading of 44 and dropping.

I am looking for trends and patterns over time.

Do the numbers correlate with how I am feeling at the time? Are there any outside factors, such as a recent meal or a stress dose of medicine, that would influence the readings? Is this a one off number, or is a pattern emerging?

I am a big advocate on the usefulness of data. However data interpreted wrong can be harmful. Have you ever wondered why there is no y-axis on my Theoretical Steroid Curve Plotter? This was done purposefully, as I have zero desire to explain to the masses the theory behind differential equations. If I provided a scale on the y-axis, there would be a high chance that someone would interpret that number wrong which would lead them to physical harm. Nope. I refuse to do it.

The same is true with my now 24/7 access to glucose readings. If I am not carefully looking at the big overall picture, I can get myself into trouble by focusing on just the individual numbers. In the four steps of data analysis, I am currently wrapping up step three. I have already communicated with my endo, and he agrees with the conclusions that this study has shown us.

It is important to note that with all data analysis, you must sanity check your conclusions. Otherwise, you run the risk of great harm.


In summary, I still find this Constant Glucose Monitor an incredibly useful tool to help me manage my Adrenal Insufficiency and Cortisol Pump rates. But you must be mindful of the limitations of this tool. Like everything in life, this just tells part of the story and part of the narrative.

Be careful with how you interpret the data.

And check back for more things I have learned through this CGM. Like I mentioned previously, I do plan on publishing my findings here on this blog so that others in our community can benefit from them as well. Let us never stop learning about this disease. Let us remain always Clearly Alive.

Amber Nicole is Clearly Alive