*ACE/AACE A1C Target for Glycemic Control

According to the ACE/AACE guidelines on A1C higher than 6.5% is a warning sign that your diabetes is out of control. If your hemoglobin A1C is high, your healthcare team may change your diabetes plan to help control your blood sugar better. Changes in your plan are expected from time-to-time and will help bring your A1C closer to normal. When your A1C is close to normal, you know you are doing all you can to stay healthy.

Research shows that good blood sugar control may lower your risk of major health problems including:

• heart disease 
• stroke 
• kidney disease 
• eye disease 
• nerve damage 
• amputations 
• circulation problems

HbA1c Measurement

In the blood, glucose binds irreversibly to hemoglobin molecules within red blood cells. The amount of glucose that is bound to hemoglobin is directly tied to the concentration of glucose in the blood. Since red blood cells have a lifespan of approximately 90 days, measuring the amount of glucose bound to hemoglobin can provide an assessment of average blood sugar control during the 60 to 90 days prior to the test. This is the purpose of the glycated hemoglobin tests, most commonly the hemoglobin A1c (HbA1c) measurement. Since the test results give feedback on the previous two to three months, getting an HbA1c test done every three months will give you good data on your average blood sugars. If you get an HbA1c every six months, you'll miss out on three months worth of information that could help you manage your diabetes. 

Variations in Standards
There are several methods for measuring HbA1c, and results from one method cannot be compared directly with results from another method. You must compare your measurement with the standards for the method of measurement that was used, usually against the highest non-diabetic value. The National Glycohemoglobin Standardization Program aims to to standardize glycohemoglobin test results so that clinical laboratory results are comparable to those reported in the Diabetes Control and Complications Trial. 

Note also that different patterns of blood sugar values can result in similar HbA1c values. For example, one person may have an irregular pattern of blood sugars, with lots of highs and lows, and an average blood sugar level of 200 mg/dl. Another person may have a very regular blood sugar level of around 200 mg/dl all the time. Though both will have similar HbA1c levels, they have very different situations that require different actions to remedy. Frequent home blood glucose monitoring will provide the detailed information about the pattern of blood sugars to help each person decide how to adjust the insulin to improve their average control. 

HbA1c and Blood Sugar Values

Your HbA1c value can tell you what your average blood sugar has been for approximately the previous three months. The chart below shows the approximate relationship between HbA1c and average blood sugar values, as reported in the DCCT.

Factors that interfere with GHB (HbA1c) Test Results 

Hemoglobin Variants and Derivatives: Genetic variants (e.g. HbS trait, HbC trait) and chemically modified derivatives of hemoglobin (e.g. carbamylated Hb in patients with renal failure, acetylated Hb in patients taking large amounts of aspirin) can affect the accuracy of GHB measurements. The effects vary depending on the specific Hb variant or derivative and the specific GHB method. information for most of the commonly used GHB methods for the some of the more common Hb variants and derivatives. Interferences from less common Hb variants and derivatives , When selecting an assay method, laboratories should take into consideration characteristics of the patient population served, (i.e., high prevalence of hemoglobinopathies or renal failure).

Shortened Erythrocyte Survival: Any condition that shortens erythrocyte survival or decreases mean erythrocyte age (e.g., recovery from acute blood loss, hemolytic anemia) will falsely lower GHB test results regardless of the assay method used . GHB results from patients with HbSS, HbCC, and HbSC must be interpreted with caution given the pathological processes, including anemia, increased red cell turnover, transfusion requirements, that adversely impact GHB as a marker of long-term glycemic control. Alternative forms of testing such as glycated serum protein (fructosamine) should be considered for these patients.

Other factors: Vitamins C and E are reported to falsely lower test results, possibly by inhibiting glycation of hemoglobin ; vitamin C may increase values with some assays . Iron-deficiency anemia is reported to increase test results . Hypertriglyceridemia, hyperbilirubinemia, uremia , chronic alcoholism, chronic ingestion of salicylates, and opiate addiction are reported to interfere with some assay methods, falsely increasing results

HbA1c Measurement Conversions