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What Not to Trust

Oct 23, 2018

Author: Joy Pape, MSN, FNP-C, CDE, WOCN, CFCN, FAADE

I received a call and glucose numbers from patient who has type 2 diabetes, usually with hyperglycemia, never hypoglycemia. I noticed there was at least a 12-hour span since the last glucose reading. His glucose levels after the over-12-hour lag showed hypoglycemia during the  night when the numbers start showing. His glucose averaged 53 during that time, but it has been running 150 and over, and we have been slowly increasing his insulin.

The patient denied symptoms of hypoglycemia and reported a fasting fingerstick of 176 mg/dL. At the time time he checked his glucose, the CGM showed 114, but his fingerstick was 176 mg/dL. As mentioned, we are working on getting his numbers more in normal range.


I reiterated to the patient that often the first 24 hours on a new sensor is not accurate. I recommended he not make any changes today, but check fingerstick if glucose is out of his normal range. He agreed.

The disaster could be that people can make adjustments — the wrong type of adjustments — in response to a time when the CGM is less than accurate, usually the first 24 hours.

Lessons Learned:

  • Always treating from a CGM is not always the way to go.
  • The first 24 hours after inserting a new sensor may not be accurate for all patients. Teach patient this and to check fingerstick during this time and whenever in doubt.


Joy Pape, FNP-C, CDE
Medical Editor, Diabetes In Control

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