Switching to a CGM: What Surprised Me

Gingerly pressing the plastic applicator against my belly, I stand at the bathroom counter. Looking in the mirror, I wince in anticipation. I’ve done this enough times to know it won’t hurt. It won’t even pinch. But somehow I’m still not 100% comfortable with attaching this thing to my body.

The spring releases, making a clicking noise. My finger smooths the adhesive tape along the sensor’s edge. Success. The white metal disk should stay attached for the next 14 days. With a wry smile, I think to myself, “I’m a star-bellied Sneetch!”

With this thing, this continuous glucose monitor (CGM), I can easily keep track of my glucose levels continuously and in real time. That’s the promise made.

At first, it didn’t seem like a promise kept.

The comfort of the fingerstick

Before using a CGM, I religiously poked my finger as many as seven times a day, checking my glucose levels and dutifully noting the readings in my tracking app. My glucometer was extremely accurate. Its A1C estimate matched my lab results. In the 18 months following my diagnosis, my glucometer helped me cut my A1C by nearly half. I trusted it.

Getting a CGM was exciting. It was up-to-date technology. Way fewer fingersticks needed. Maybe the skin on my fingertips would soften up. Checking my glucose levels with just a glance at my phone. One less extra diabetes thing to drag around.

When the numbers don't match

And then I compared my CGM’s readings to my glucometer’s.

They didn’t match. Not even close.

The manufacturer’s guidance says to expect up to 20% variation between the readings from their CGM and a fingerstick. That’s a big gap. Of course, the CGM and glucometer measure different fluids. The CGM uses the fluid just beneath the skin, and the glucometer uses blood. There's a time lag between the two readings.

I tried doing a fingerstick, then waiting 15 minutes to check the CGM so that it could catch up. Still, the numbers didn’t match. I wondered how much I could trust what the CGM told me. Should I have switched monitoring methods?

A shift in perspective

When I shared my doubts with my diabetes pharmacist, they suggested something radical: Change the way I look at the readings.

Instead of focusing on a single point, a number at a particular time of day, look at the day’s line. Open up my view to an overall picture of what’s happening.

• How much of the time is the line that indicates my readings in the shaded area that represents being in range?
• Is that line flat or nearly so? Or does it jump up and down wildly like a Richter scale during an earthquake?

What they suggested kind of blew my mind.

Finding the rhythm

I started looking at the overall rhythm of the day instead of obsessing over a high or low. The rise after my morning coffee and toast. The calm dip from a short after-dinner walk. Turns out, my glucose levels love a nap.

Looking at it all together reminds me again and again that no single reading makes or breaks anything. What matters is the overall pattern. And that little metal disk on my belly makes that possible.