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A1C: Diagnosing and Monitoring

A1C – the glycated hemoglobin test, commonly used as a clinical tool to diagnose diabetes and assess glycemic control. It can be measured at any time of the day, eliminating patient fasting, and it provides valuable information about recent glycemic control.

So, what A1C tells us? The A1C reflects an individual’s average blood glucose values in the 8 to 12 weeks before measurement. Glucose affixes to the hemoglobin protein in the oxygen-transporting red blood cells, which are constantly turning over and have an average life span of 3 months. The A1C is the percentage of glycation during the life of RBC and HgA1C molecule.

The American Diabetes Association current A1C recommendation of 7% or lower.

False highs and lows conditions:

  • sickle cell anemia
  • hemolytic anemias
  • fetal hemoglobin >25% (early pregnancy can alter the value because of red blood cell production by the fetus and dilutional anemia from expanded blood volume. for those reasons, A1C shouldn’t be used to diagnose gestational diabetes)
  • carbamylated and acetylated hemoglobin
  • End-stage renal disease can result in falsely low A1C values
  • Whites have an absolute A1C reading 0.1% to 0.4% lower than Asian, African American, and Hispanic individuals (why? not well understand)

Diabetes Dx Criteria (the American Diabetes Association):

  • Fasting plasma glucose greater or equal 126mg/dL
  • 2-hour plasma glucose greater or equal 200 mg/dL during glucose tolerance test
  • A1C greater or equal 6.5% with testing done using standardized diabetes control and complications trial assay
  • Random plasma glucose greater or equal 200 mg/dL with symptoms of hyperglycemia (polyuria, polydipsia, and polyphagia)


Resource retrieved from: Pereira, K. (2017) Insights into glucose monitoring for diabetes: Developments in testing provide better outcomes for your patients.

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