I started using a continuous glucose monitor (CGM) almost 10 years ago. Reviewing my CGM data quickly became a daily habit for me. Time-in-range, time low, average glucose and standard deviation data numerically characterized the quality of my glucose metabolism.
I soon observed that my A1c (glycated hemoglobin) and its associated average glucose did not agree. My A1c number consistently sat about 0.5% above the average measured by my CGM and my finger-stick meter.
My first attempt to resolve this discrepancy was a hypothesis that my fingerstick meter, the device I used to calibrate my CGM, was inaccurate and the reason for the A1c/average glucose discordance.
I began to do three fingerstick meter measurements at the same time as a lab glucose blood draw. My meter, however, agreed closely with the lab draw. Last December, for example, three fingersticks came in at 92, 88, and 88 mg/dL (5.1, 4.9, 4.9 mmol/L). I employed three different pokes using three different fingers across both hands.
The average of these three equated to 89 (4.9). The lab plasma glucose weighed in at 89 mg/dL or 4.9 mmol/L. I’ve repeated this exercise four times per year for the last three years and found similar results. My meter was not the cause of the A1c/average glucose disagreement.
I’ve done lots of reading about this topic and the best, yet still unsatisfying reason, was Dr. Irl Hirsch’s explanation that the A1c just does not precisely equate to a discrete average glucose value. We’ve all seen the doctor exam room posters that display a 6.0% A1c that indicates an average BG of 126 mg/dL (7.0 mmol/L).
Yet, Dr. Hirsch has written that people with a 6.0% A1c experience average blood glucose levels anywhere from 100 mg/dL (5.6) to 152 mg/dL (8.4). People on the high side of this distribution curve, Dr, Hirsch called high glycators. At least the medical literature told me that my experience was not that unusual. But it didn’t reveal why my A1c seemed to always ride about 0.5% above my glucose experience.
I started seeing a naturopathic physician recently to seek help implementing lifestyle changes to address a coronary artery disease diagnosis last fall. Her recent lab order included a complete blood count or CBC panel. The results showed that my hematocrit, hemoglobin, and red blood cell count all came in at just below the lower lab threshold. I have iron deficiency anemia!
This was unexpected and news to me. I quickly searched my lab history and was surprised to see that the CBC panel had not been run since 2011 and 2009. And those labs were ordered by one physician who repaired a hernia and another doctor who was conducting a study. The 2009 numbers for hematocrit, hemoglobin, and red blood cell count were all within the lab range but at the low end. The 2011 showed all these measures trending downward with one of the three sinking below range. I’ve been trending anemic for almost nine years now.
None of my three endos during that time ordered a CBC panel. Yet I distinctly remembered commenting to them about the A1c/average glucose discordance. One of those endos diagnosed me with sinus tachycardia or rapid heart-rate. She quickly prescribed a beta-blocker drug and showed no curiosity about the root cause. Turns out anemia often drives a rapid heart rate. This makes sense. Anemia impairs the blood’s ability to distribute oxygen to all the body’s tissues. A threat to oxygen levels leads to the heart pumping more quickly to overcome that deficit.
Inappropriately cold hands and feet are another symptom I reported to my docs over the years and these comments elicited little follow-up or curiosity. Cold extremities are also a symptom of anemia.
I take pride in my consistent monitoring of the medical literature to inform health choices, but I totally missed this one. I guess, since I didn’t know I was anemic, I didn’t pay much attention to the literature that discussed anemia and its effects on A1c, but it’s clear now that I should have.
Here’s a 2014 National Institute of Health (NIH) study that describes my A1c/average glucose disagreement that puzzled me for the last 10 years.
These two figures tell the story.
Here’s the simple conclusion made in this study.
Iron deficiency anemia elevates HbA1c levels in diabetic individuals with controlled plasma glucose levels. The elevation is more in patients having plasma glucose levels between 100 to 126 mg/dl. Hence, before altering the treatment regimen for diabetes, iron deficiency anemia should be considered.
I’m happy to have discovered this connection after so many years. I’m disappointed in my doctors’ failure to pick up on this basic health measure. If they had invested a tenth as much attention to symptoms that I repeatedly reported to them as they were hyper-vigilantly distracted by potential hypoglycemia, they would have detected my hiding-in-plain-sight anemia. I’m also disappointed that I didn’t put 2 +2 together sooner. Live and learn!
I’ve started a daily iron supplement and I suspect in the months ahead that my A1c will finally come into agreement with my average glucose as measured by my CGM and finger-stick meter.