Normal, High, and Low Hemoglobin A1C Levels

Hemoglobin A1c (HbA1c) or Glycosylated Hemoglobin is a Normal Hemoglobin Variant. It is a subtype of Hemoglobin A1 which is found normally in adults blood.


Hemoglobin A1 is a normal type of Adults Hemoglobin (Hemoglobin A). Hemoglobin A1 binds strongly with glucose molecules found in blood. Hemoglobin A1 has three subtypes; A, B, and C. Hemoglobin A1C is that subtype of Hemoglobin A which binds the most glucose if compared with types A and B of Hemoglobin A1. For this reason Hemoglobin A1C is used to monitor the glucose level in diabetic adults.

When people fast or don’t consume sugar for long period of time, their blood sugar levels decreases dramatically. And vice versa,  when people eat a sweet snack,  their blood sugar increase dramatically. This behavior doesn’t qualify blood sugar levels to be used in order to monitor how a diabetic patient’s blood glucose levels are being affected by their diet and treatment.


On the other hand, as the RBC circulates, it combines its HbA1 with some of the glucose in the bloodstream to form glycohemoglobin (GHb). The amount of GHb depends on the amount of glucose available in the bloodstream over the RBC’s 120-day life span. Therefore determination of the GHb value reflects the average blood sugar level for the 100- to 120-day period before the test. The more glucose the RBC is exposed to, the greater the GHb percentage. One important advantage of this test is that the sample can be drawn at any time, because it is not affected by short-term variations (e.g., food intake, exercise, stress, hypoglycemic agents, patient cooperation). It is also possible for very high short-term blood glucose levels to cause an elevation of GHb. Usually, however, the degree of glucose elevation results not from a transient high level but from a persistent, moderate elevation over the entire life of the RBC.


Hemoglobin A1c test is used to monitor diabetes treatment. It measures the amount of HbA1c in the blood. This test provides an accurate long-term index of the patient’s average blood glucose level. However, Hemoglobin A1c test cannot be used in diagnosis to determine if the patient is diabetic or not.


Like GHb, the glucose can nonenzymatically bind to proteins in proportion to the mean blood glucose level. The glycated protein is stable until the degradation of the protein. Recall that the average life span of an RBC (and the GHb within) is 120 days. The GHb, therefore, may not reflect more recent changes in glucose levels. Because the turnover rate of proteins is much faster than that of hemoglobin, the measurement of serum glycated proteins (such as glycated albumin or fructosamine) provides more recent information about glucose levels. Glycated proteins reflect an average blood glucose level of the past 15 to 20 days. Although an initial single glycated protein result may not separate good glucose control from poor control, serial testing provides a much better indication of glucose control.


The GHb or glycated proteins tests are particularly beneficial for the following:

  1. Evaluating the success of diabetic treatment and patient compliance.
  2. Comparing and contrasting the success of past and new forms of diabetic therapy.
  3. Determining the duration of hyperglycemia in patients with newly diagnosed diabetes.
  4. Providing a sensitive estimate of glucose imbalance in patients with mild diabetes.
  5. Individualizing diabetic control regimens.
  6. Providing a sense of reward for many patients when the test shows achievement of good diabetic control.
  7. Evaluating the diabetic patient whose glucose levels change significantly from day to day (brittle diabetes).
  8. Differentiating short-term hyperglycemia in nondiabetics (e.g., recent stress or myocardial infarction [MI]) and diabetics (in whom the glucose has been persistently elevated).


By a relatively simple calculation, GHb can be correlated accurately with the daily mean plasma glucose (MPG) level, the average glucose level throughout the day. This has been very helpful for diabetics and their health care professionals in determining and evaluating daily glucose goals. There is a linear relationship between A1c (GHb) and PG:
With a Pearson correlation coefficient (r) of 0.82. Each 1% change in GHb represents a change of approximately 35 mg/dL MPG or 2 mmol/L.




Normal Hemoglobin A1C Levels

A healthy person normally has a Hemoglobin A1C level ranging between 4% and 5.9%. Hemoglobin A1C levels increase in diabetic patients, a patient with a good diabetic control usually have a Hemoglobin A1C level less than 7%. As Hemoglobin A1C levels increase, this would be an indication that the patient’s body is not able to tolerate the blood sugar levels. A diabetic patient who has A1C level above %9 would have a serious diabetic condition. Again, Hemoglobin A1C test is used only to keep track on the patient’s diabetic control. A1C test cannot be used to diagnose diabetes and the values here wouldn’t indicate that the patient is diabetic or not.


Hemoglobin A1C test cannot be used to monitor the diabetic control of patients who have Hemoglobinopathies. Hemoglobinopathies are genetic conditions that occur when the body is not capable of producing normal Hemoglobin Variants instead of producing Hemoglobin A, and Hemoglobin A1C as well. Sickle-cell Anemia is a common example of Hemoglobinopathies. Since the body cannot produce Hemoglobin A1C in such conditions, hemoglobinopathies will cause inadequate results of A1C test that physicians cannot rely to monitor and treat diabetes.




Causes of High Hemoglobin A1C Levels

High Hemoglobin A1C Level are usually caused by diabetes and poor diabetic control. However, there are conditions and factor that elevate Hemoglobin A1C levels in blood other than being diabetic. Non-diabetic Hyperglycemia for example occurs when high amount of glucose circulate in the plasma which causes Hemoglobin A1c and other glycated proteins to be found in persistently high levels.


Causes of hyperglycemia other than diabetes include conditions like Stroke, Acute Stress Response, Cushing Syndrome,  Myocardial Infraction, Pheochromocytoma, Glucagonoma, corticosteroid therapy, and Acromegaly. Patients may develop hyperglycemia by taking drugs including Corticostroids, Protease Inhibitors, and Beta Blockers.


Some women may have pregnancy accompanied with hyperglycemia. This is a condition known as Gestational Diabetes. Gestational Diabetes occurs as a result of the changes female bodies experience during pregnancy.


Patients who have Splenectomy (Spleen removal procedure) experience longer than normal Red Blood Cell life. As Hemoglobin A1C accumulates within Red Blood Cells over time, longer RBC life leads to High Hemoglobin A1C levels.



Causes of Low Hemoglobin A1C Levels

Conditions that cause Low Hemoglobin A1C levels are not as common as those that cause High Hemoglobin A1C levels. Causes of Low Hemoglobin A1C Levels include:


  • Hemolytic Anemia, which is a form of Anemia that occurs when Red Blood Cells breakdown before they reach their normal life time of approximately 120 days. The short life time of Red Blood Cells in such a case causes Hemoglobin A1C to not accumulate for a long enough period of time causing Low Hemoglobin A1C Levels.
  • Chronic Renal Failure causes Hemoglobin A1C levels to be decreased because the body wouldn’t be able to produce enough Erythropoietin. Erythropoietin is a hormone produced in the kidneys and it controls the production of Red Blood Cells. A lack Erythropoietin reduces the production of Red Blood Cells leading to low Hemoglobin A1C levels as well.