A low result on a hemoglobin A1C test can be a confusing finding. The A1C test provides an average measure of blood sugar control over approximately the past two to three months, making it a valuable tool for diabetes screening and management. While a high A1C suggests a risk for prediabetes or diabetes, a result on the lower end of the spectrum is not automatically a sign of optimal health. It can indicate a genuine state of low blood sugar or an issue that is causing the test result to be inaccurate, both of which may require medical attention.
Understanding How A1C is Measured
The A1C test, also known as glycated hemoglobin or HbA1c, measures the percentage of hemoglobin proteins in red blood cells that have glucose attached. This attachment process, called glycation, is permanent for the lifespan of the red blood cell, which is about 90 to 120 days. Therefore, the test provides a picture of your average blood glucose levels over that period, rather than a single point in time measurement.
For individuals without diabetes, the normal A1C range is typically considered to be below 5.7%. A result between 5.7% and 6.4% indicates prediabetes, and 6.5% or higher suggests diabetes. An abnormally low result generally falls below 4.0% to 4.5%, which is often below the established reference range for a healthy person.
Medical and Lifestyle Factors That Lower A1C
A low A1C result can be categorized into two groups: a genuinely low average blood sugar level or a falsely low reading caused by issues with the red blood cells themselves.
Genuinely Low A1C
A genuinely low A1C often suggests that a person is experiencing frequent episodes of low blood sugar, known as hypoglycemia. This can occur in people with diabetes who are receiving aggressive treatment with insulin or other glucose-lowering medications.
In people who do not have diabetes, a consistently low A1C can point to rare conditions causing non-diabetic hypoglycemia. Examples include an insulinoma, which is a tumor in the pancreas that releases excessive amounts of insulin, leading to chronic low blood sugar. Adrenal disorders, such as adrenal insufficiency, can also cause low blood sugar because the body lacks the cortisol hormone needed to counteract insulin and raise glucose levels. Significant dietary changes, like extreme carbohydrate restriction or prolonged fasting, may also contribute to a lower average blood sugar level.
Falsely Low A1C
A falsely low A1C is caused by anything that shortens the lifespan of the red blood cells. Since the A1C test relies on the red blood cells surviving for the full 90-day period, conditions that cause them to be destroyed prematurely will artificially lower the result.
These issues include hemolytic anemia, which involves the rapid destruction of red blood cells, or significant acute or chronic blood loss. Certain genetic conditions affecting hemoglobin, such as sickle cell trait or thalassemia, can also interfere with the test.
Clinical Significance and Risks Associated with Low A1C
A low A1C is considered a concern because it can mask an underlying condition or indicate an immediate health risk. The most direct danger of a genuinely low A1C is the increased risk of severe hypoglycemia. Episodes of acute low blood sugar can lead to symptoms like confusion, dizziness, fainting, and, in severe cases, seizures or loss of consciousness.
A falsely low A1C is dangerous because it can lead to a misdiagnosis or undertreatment of diabetes. If a person has high blood sugar but also has a condition like anemia that is shortening their red blood cell lifespan, their A1C result will appear normal or low. This false reassurance can delay necessary treatment and increase the risk of long-term diabetes-related complications.
Furthermore, a low A1C can serve as an unexpected indicator for other serious systemic diseases. Studies have shown that very low A1C levels, particularly below 4.0%, are associated with an increased risk of all-cause mortality in adults without diabetes. These low readings can be a red flag for conditions such as severe liver disease or kidney failure, which both affect glucose metabolism and red blood cell turnover.
When to Seek Further Medical Evaluation
If an A1C result falls below the normal range, or is unexpectedly low for a person with known diabetes, it is important to consult with a healthcare provider. The initial step typically involves a comprehensive medical review to check for symptoms of hypoglycemia or any signs of underlying disease. The doctor may order a complete blood count (CBC) to check for anemia or other red blood cell issues that could be skewing the result.
To confirm actual average blood sugar levels, alternative tests may be utilized, such as the fructosamine test or glycated albumin. These tests measure glucose attachment to other proteins in the blood that have a shorter lifespan than hemoglobin, providing an average over the preceding two to three weeks.
Continuous Glucose Monitoring (CGM) may also be recommended to capture real-time blood sugar fluctuations and identify frequent episodes of hypoglycemia that the A1C test missed. If the low A1C is due to overtreatment of diabetes, the medical team will work to safely adjust medication doses to prevent future low blood sugar events.