Hemoglobin A1C

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

The normal lifespan of a red blood cell is 120 days. During this time, glucose combines with hemoglobin producing a substance called glycohemoglobin. The amount of glycohemoglobin formed is in direct proportion to the amount of glucose present in the blood stream during the lifespan of the red blood cells. When blood glucose levels are high, such as in diabetes, the amount of hemoglobin that is glycosylated to form glycohemoglobin increases. This process is difficult to reverse especially in adults or those that have had diabetes for a long period of time. Hence, the longer blood glucose levels remain high and the greater the amount of glucose in the blood, the more glucose will attach to the red blood cells.[1], [2]


  • This test is used to monitor diabetes control. It is helpful in determining therapeutic options for treatment and management of diabetes.
  • This test is used in conjunction with other blood tests, such as blood glucose and serum insulin and glucose challenge, to diagnose Diabetes.
  • The hemoglobin A1C test indicates the amount of non-enzymatic glycosylation that occurs on a minor sub-type of hemoglobin called A1C.
  • This test shows the average levels of blood glucose in a 2-3 month period before the test.
  • There appears to be a seasonal variation to Hb1aC levels in young adolescents, especially those with Type I Diabetes. The lowest values were observed in August and September and the highest were noted in February, March, April, November and December.[3]

Patient Preparation

  • No fasting required.
  • Factors which can cause increased levels
  • presence of different sub-types of hemoglobin molecules e.g. hemoglobin F and uremia, lengthening of RBC life span, anemia
  • high levels of CRP are associated with increased levels of hemoglobin A1C
  • Factors which can cause decreased levels

Clinical Implications

The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range <7% 0.07
Optimal Range 4.1-5.7% 0.041-0.057

Note: The results are expressed as a percentage of total hemoglobin.

High levels indicate:

Low levels indicate:

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J, (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain
  3. Mianowska B, Fendler W, Szadkowska A, Pietrzak I, Baranowska A, Młynarski W 2011 One-year variability of HbA1c in children and adolescents with type 1 diabetes - preliminary results Pediatr Endocrinol Diabetes Metab;17(1):20-5. PMID: 21489352