If you’re using a CGM (continuous glucose monitor), you know they can quite literally be a lifesaver. You also know that there can be some issues calibrating one to match your fingerstick readings.

Sometimes the issue is just the warm up period in the first 24 hours after putting on a new unit. Other times it can be something more innocuous that is cause the numbers to not match up.

Case in point: today it is hand soap.

I have been getting a difference of about 25 points from fingerstick to CGM readings. How? Well it turns out that some soaps contain glycerol or glycerine, which the FDA considers a carb. The residue then combines with the small amount of blood you draw to produce a higher-than-it-should-be reading.

To combat this, use dish soap to wash your hands (or one that doesn’t contain glycerol, glycerine, or fruit extracts) prior to a fingerstick and follow it up by using an alcohol wipe to sterilize the finger you are going to use for testing. Allow it to air dry first and you should be good to go!