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When is HbA1c not accurate?

Updated: Mar 19, 2020

Hemoglobin A1c is a widely accepted tool for monitoring glycemic control. It clinically convenient and is not susceptible to acute variability in glucose fluctuations. The 1970’s DCCT trial showed its importance in predicting diabetic outcomes and complication risk in PWD.’ It’s clear that HbA1c can be a very good indicator of control. I don’t think anyone can debate this. The problem is when it is used as the only indicator of control. How many of your clinicians rely solely on your HbA1c? HbA1c is not “the big picture”. Put simply, HbA1c is an indication of how much glucose has bound to hemoglobin, or a red blood cell, over its lifespan (3 months). It cannot tell us anything about glucose fluctuations, quality of life, or time in range (the new gold standard-in my opinion). But because HbA1c is so heavily weighted, it’s important to know when it is not accurate. HbA1c can be falsely elevated any time there is a condition which prolongs the life of the red blood cells. Some examples of this include iron deficiency anemia, B12 anemia, folate deficiency anemia, and asplenia (absence of normal spleen function). Additionally, blood transfusions can result in elevated (or decreased) HbA1c levels. Significant hypertriglyceridemia (high triglycerides > 1,750 mg/dL), and significant hyperbilirubinemia (high bilirubin >20mg/dL) can elevate HbA1c and ingestion of certain drugs such as excessive alcohol, opiates, and salycilates can also be significant. Falsely low HBA1c’s can occur in conditions which shorten the lifespan of the red blood cells such as in pregnancy or splenomegaly (spleen enlargement). Chronic blood loss, vitamin E ingestion, and vitamin C ingestion can also cause the same.

This is why it is important to look at the BIG PICTURE when evaluating diabetes and particularly why time in range (time spent between 70-180mg/dl) has become a good tool in evaluating diabetes in conjunction with HbA1c. I know this stuff is complicated… but I guess if there is one thing that you get out of this post it’s that I want to encourage you to ask questions. Both you AND your diabetes is more than just an A1c. Please make sure you are treated that way!


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