Sick Day Surprise

I write and speak to patients often about how illness complicates the management of diabetes. In fact, I wrote a post earlier this year I called “Sick Day” Diabetes Self Management where I described the common fights we have with high blood glucose readings when we’re ill, and I had, in fact, been sick. Well, just last week I was sick again – the good old common cold – in spite of the fact that one of my recommendations is to do everything possible to prevent illness. I suppose this latest episode proves how hard prevention can be.

Fighting a cold with diabetes

But this last episode had a peculiar twist, and it’s still a mystery to me. One evening my continuous glucose monitor (CGM) showed “LO” when I scanned my sensor, which would indicate that my blood glucose level was 40 mg/dl or lower. Since I didn’t feel low I decided to do a finger stick, and was somewhat surprised to find my actual blood glucose level around 80. Over the course of the next few days, I tracked my blood glucose levels comparing the sensor (CGM) reading to a conventional finger stick. Again and again, I found the difference between the two unacceptably different.

CGM vs. finger stick readings

I should point out that the CGM does not directly measure blood glucose – instead, it measures glucose levels in what’s called interstitial fluid (the fluid between cells). So, it’s well known and acceptable that the sensor level would lag behind actual blood glucose measurements. In fact, I sometimes do a finger stick just to see which direction my levels might be trending. If my sensor reading was, for example, 180 I’d like to see my blood glucose reading lower than 180 – trending down. I understand how the readings can be different, and that is absolutely not what I was experiencing during my illness.

I can’t actually tell you what was happening. I do know that this mysterious pattern returned to normal as I began feeling better, and it was the same sensor. It seemed related to my illness, and I know that illness does mysterious things to our blood sugar levels. I could not say after this single experience that illness was the cause. If you are using a CGM I would recommend comparing reading with a finger stick, however. And, please let me know if you had a similar experience by commenting below. Feel better soon.