HBA1C TEST: WHAT FACTORS AFFECT ITS RESULTS?
Medically Reviewed and Updated by Dr. Sony Sherpa, (MBBS) - September 04, 2024
Several medical tests exist today. Usually, these tests are done to diagnose certain diseases. Other times, they are carried out as part of routine medical check-ups. The HbA1c test is one such medical test to monitor a condition.
As with most medical tests, it begins and ends with taking a blood sample which is then analyzed in a laboratory. But how important is it in monitoring one’s health status, and what can affect its results? We will discuss these and many more as you read further.
What Does HbA1c Mean?
“Hb” is an acronym for hemoglobin, a protein in red blood cells whose primary function is to carry oxygen inhaled around the body. HbA1 is the common variant of this protein present in healthy individuals. However, while transporting oxygen, hemoglobin could bind to excess glucose or sugar in the blood. This is when it becomes HbA1c which serves as a measure that reflects average blood sugar levels over about 2 to 3 months.
What Is the HbA1c Test?
Glycated hemoglobin test, glycohemoglobin test, and glycosylated hemoglobin test are all other names for the HbA1C test. It is a laboratory blood test that measures the average blood sugar level in the body over 2 to 3 months. Before being replaced, red blood cells have an average lifespan of four months. Hence the test is performed at these intervals. This helps diagnose diabetes and monitor it long-term.
The HbA1c test is carried out by a health professional who takes a blood sample from a vein in the arm using a small needle and then collects it in a test tube taken to the laboratory. The entire test’s duration is usually less than five minutes and does not require fasting or prior preparation.
Role of the HbA1c Test
When glucose from the food you take gets absorbed into the bloodstream and combines with hemoglobin, the process is called glycation. Now the rate of glycation is directly proportional to the glucose concentration in the blood. This means that if more glucose is in the blood, glycation increases, increasing the number of glycated hemoglobin molecules.
For the HbA1c test, analysis is done in the laboratory after a blood sample has been taken. A reagent is added to the sample to separate the glycated molecules from the normal ones. After this, a machine measures the hemoglobin molecules bound to glucose to report the A1c levels as a percentage.
Hemoglobin A1 and Hemoglobin A1c
Hemoglobin A1 is a normal hemoglobin component present in most healthy individuals. It is a combination of a protein component called globin and a sugar molecule called glucose. Hemoglobin A1c, on the other hand, is a subtype of the HbA1 formed when glucose molecules in the blood attach to hemoglobin itself.
It is the level of the HbA1c that forms the basis of the HbA1c test. Simply put, HbA1c is a normal component of hemoglobin, while HbA1c is an abnormal type of hemoglobin. The HbA1c test is also used to monitor blood glucose levels in people with diabetes since it serves as a measure, whereas the HbA1 does not serve this purpose. Hence, you cannot use these two interchangeably.
Normal HbA1c Levels
A healthy individual's average blood glucose level is usually below 5.7% which signifies a normal blood sugar level. If the glucose levels are higher than normal, as in prediabetes, it ranges between 5.7 to 6.4%. Understanding HbA1c Test Result
As explained earlier, the normal level HbA1c percentage is 5.7%. The HbA1c percentage is the glucose that has been bound to the blood. In other words, it states the ratio of glycated hemoglobin in the blood to the total amount of hemoglobin present, which is then expressed as a percentage. A higher percentage connotes the blood sugar level is higher than usual, while a lower rate is vice versa.
However, this test is not a substitute for standard blood glucose tests, which you can do as often as possible using a glucometer. The HbA1c test is designed for long-term control to help your doctor monitor your progress and, if need be, adjust your management plans.
Why Is Testing A1c Levels Important?
Here are a few reasons that attest to why A1c test measures are important:
- It helps diagnose diabetes early before it worsens, leading to other diabetes complications.
- It is also effective for monitoring the effectiveness of a diabetes treatment plan. The initial HbA1c test serves as a baseline measurement, providing a reference point for assessing whether blood glucose levels are improving or worsening over time. Regular HbA1c testing helps determine if the current management plan is working or if adjustments are needed.
Who Needs an HbA1c Test?
The HbA1c test is recommended by the Center for Disease Control (CDC) to test for prediabetes and diabetes if you are more than 45 years of age. In cases when the results are normal, you can repeat the test every three years, but if there are any risk factors or indicators of prediabetes, it should be repeated every 1 or 2 years to monitor changes and manage potential progression.
Also, this test is not only limited to individuals older than 45. As a younger adult, you should take this test if:
- you are overweight, or obesity is present
- you have an immediate relative (sibling or parent) diagnosed with type 2 diabetes
- your blood pressure and cholesterol levels are high
- you are mostly physically inactive on most days of the week
- your race is at risk
- you had diabetes while pregnant, or your child’s weight at birth was over 9 lbs
- you recently had a stroke or heart condition
- you have PCOS (Polycystic Ovarian Syndrome)
- you have more than two symptoms of diabetes at the same time
Factors Affecting HbA1c Test Results
Several risk factors or conditions affect the result of the HbA1c test when taken. A few of them are discussed below:
Pregnancy
Have you ever heard of gestational diabetes? It is a type of diabetes that occurs during pregnancy and raises the possibility of the mother later developing diabetes after the pregnancy. Hormonal changes during pregnancy alter insulin production, which leads to elevated blood sugar levels. This usually occurs during the second or third trimester, but after delivery, it goes away.
During pregnancy, particularly in the second trimester, blood sugar levels can fluctuate due to hormonal changes, which can affect HbA1c levels. However, HbA1c may not accurately reflect blood glucose control during pregnancy because it measures average blood glucose over a period of about 2-3 months, while pregnancy-related changes can cause more immediate fluctuations. For pregnant women, blood glucose monitoring and tests like the oral glucose tolerance test (OGTT) are often preferred to assess glycemic control and screen for gestational diabetes.
Recent or Heavy Blood Loss
If you recently lost a lot of blood or even some of it, it can also affect the result of the Hb1Ac test taken in that period. When one loses blood, the number of red blood cells in circulation is significantly reduced, and remember that hemoglobin is present in these cells.
So if the concentration of this protein in the blood has decreased, there will be few left for sugar to bind to, which means that the blood sugar level in that period will appear reduced. This means false lower HbA1c levels. If you recently lost blood, you should take more time for your body to produce new red blood cells before you take the test.
Recent Blood Transfusion
Recent or significant blood loss can affect the results of the HbA1c test. Blood loss reduces the number of red blood cells, which contain hemoglobin. Since hemoglobin is responsible for binding with glucose to form HbA1c, a decrease in red blood cells can lead to falsely lower HbA1c levels, as there is less hemoglobin available for glucose binding. To obtain accurate HbA1c results, it is advisable to wait until your body has had time to replenish red blood cells before taking the test.
Anemias and Iron Deficiency
A condition known as anemia results in a reduction in the number of hemoglobin or red blood cells in the blood. So when the amount of hemoglobin present for glycation is reduced, it lowers the HbA1c result even when the blood glucose levels over the past few months have been elevated. There are different types of anemia based on their causes, and they include:
- vitamin-deficiency anemia
- iron-deficiency anemia
- hemolytic anemia (red blood cells are destroyed faster than they are produced)
- aplastic anemia (bone-marrow not producing adequate blood cells)
- sickle cell anemia, thalassemia (production of abnormal hemoglobin) and
- anemia due to chronic diseases.
Iron is a vital component of hemoglobin, so iron deficiency can lead to iron-deficiency anemia. Conversely, excessive iron in the body can result in an increased red blood cell count, which may elevate HbA1c levels even if blood glucose levels are normal. This indicates that iron levels, the presence of conditions like anemia, and HbA1c levels are interconnected. Therefore, it is important to assess iron levels and any related medical conditions before interpreting HbA1c results to ensure accuracy.
Hemoglobin Variants
There are different variants of hemoglobin. The variant you would have is usually inherited from a gene or trait in your biological parents. HbA is the most common form of hemoglobin. However, there are HbC, HbD, HbE, and HbS, which are present in people from different regions across the globe.
These hemoglobin variants do not increase your chances of diabetes but can affect your A1C test results. For instance, a standard test designed for the common HbA being done on blood containing the HbD reduces the chances of getting an accurate result. This is why there have been modifications in how the A1C test is carried out on other hemoglobin variants in a specialized laboratory to diagnose and monitor diabetes.
Kidney Failure
Chronic kidney disease (CKD) can impair kidney function, which normally helps to eliminate excess glucose from the blood. When kidney function is compromised, glucose can build up in the body, leading to elevated HbA1c levels. Therefore, in people with chronic kidney failure, HbA1c may not accurately reflect their blood glucose levels. Even after a kidney transplant, blood glucose levels may remain elevated due to the effects of immunosuppressive medications used post-transplant.
Conclusion
The HbA1c test provides a comprehensive assessment of glycemic control by measuring the average blood sugar levels over the past few months, making it indispensable for the diagnosis and management of type 2 diabetes. However, certain factors can influence the accuracy of the HbA1c test.
Therefore, a thorough assessment by a healthcare professional is necessary before conducting the test to ensure reliable results. It is's also important to discuss any changes in your health since your last HbA1c test and ask questions to ensure you receive an appropriate treatment plan.
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- The A1C Test & Diabetes
- All About Your A1C
- Role of Glycated Proteins in the Diagnosis and Management of Diabetes: Research Gaps and Future Directions
- Hemoglobin and Hematocrit
- Significance of HbA1c Test in Diagnosis and Prognosis of Diabetic Patients
- Diabetes & Prediabetes Tests
