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The A1C test is a blood test that reflects the average blood-glucose level over the last two to three months. Blood sample to check A1C can be taking at any time of the day, does not require fasting.

History of A1C test

In 1950s, hemoglobin A1c was identified as one of the largest fractions of the minor components of normal adult hemoglobin. Followed by different discoveries and in 1976, Koenig and colleagues demonstrated that HbA1c concentration was an indicator of fasting blood-glucose concentrations. HbA1c concentrations decreased as diabetes control improved with treatment.

What is A1C test?

A1C test

Hemoglobin is a protein in the red blood cell, which transports oxygen from your lungs to the whole body. This hemoglobin get glycosylated by glucose called as glycated hemoglobin. The blood-glucose level decides the volume of glycosylation reaction and the level of glycated hemoglobins. The life of red blood cell in our body is approximately three months (120 days). Thus, A1C provides the average blood glucose over three months.

HbA1c is a simple blood test measures the percentage of hemoglobin variant “A’ subtype ‘1c” that has been attached to the glucose in the blood. To find HbA1c, have to count the percentage of red blood cells attached to glucose.

This test measures as a percentage of glycated hemoglobin; for example, an A1C of 4.5% does mean 4.5% of the total hemoglobin has glucose attached to it.

Our glucose meter measures blood glucose directly in the blood in mg/dl or mmol/l. For example, blood glucose of 90 mg/dl means 90 mg of total glucose in the deciliter of blood or blood glucose of 5 mmol/l means 5 mmols of glucose in a liter of blood.

However, blood-glucose levels in the preceding 30 days can make more effect in the A1C than the 90 to 120 days earlier. That is why A1C level rise or drop quickly within 30 days of stringent or badly managed diabetes respectively. 

If you are having A1C percentage, it looks less meaning, until you convert it into equivalent blood-glucose level help provide more meaning. You can learn more by visiting A1C chart & calculator

How is the blood sample collected for A1C testing? 

HbA1c tests can easily do with a regular finger stick or a blood sample drawn from a vein in your arm like testing for blood glucose. Blood sample to check A1C can be taking at any time of the day, fasting not required. Home tests are now available too; they are subject to inaccuracy, if not conducted exactly as stated in the instructions.

Types of method to measure HbA1C

Four basic types of methods are in use to measure HbA1c; they are:

  1. Immunoassay,
  2. Ion-exchange high-performance liquid chromatography (HPLC),
  3. Boronate affinity HPLC,
  4. Enzymatic assays

Laboratories should be aware of their method limitations with respect to interference from the most prevalent Hb variants. They can also select new methods that are less likely to have interference. As with any laboratory test, any result that does not fit the clinical picture should require investigation further with the clinician.

Ask your doctor if the lab running the test uses a method that has certified by the NGSP. Sadly, however, not every laboratory or home test kit meets those standards. List of NGSP Certified Laboratories.

Factors affecting HbA1C

A1C can be increases or decreases by certain factors; they are:

  1. Decrease or increase in erythrocyte (decrease in RBC) can make you A1C to lower or increase respectively.
  2. Hb Variants - Hemoglobin S trait, which affects about 8% of African Americans, hemoglobin C trait, which affects approximately 3% of African Americans, and hemoglobin E trait, which affects 10% to more than 50% of Southeast Asians in California, are all reported to affect some HbA1c assay methods. Elevated hemoglobin F, which is associated with thalassemia syndromes, also affects some assay methods.
  3. Hypertriglyceridemia interfered with some assay methods and falsely increasing results.
  4. High bilirubin interferes with some assay methods and falsely increasing results.
  5. Aspirin interfered with some assay methods and falsely increasing results.
  6. Vitamin C & E ingestion interfered with some assay methods and falsely decreasing results.
  7. Chronic alcohol abuse produces false high.
  8. A splenectomy is a surgical procedure that partially or completely removes the spleen, will falsely raise A1C.
  9. Chronic liver disease – has false A1C low.

Causes of decrease in erythrocyte (lower A1C):

  1. Anemia & thalassemia or hemolytic anemia, liver disease
  2. Hemorrhage or bleeding - heavy menstrual periods in women and stomach ulcers,
  3. Hemolysis (RBS destruction) - due to transfusion, blood vessel injury, or other causes,
  4. An erythropoietin deficiency - secondary to kidney diseases, Uremia (BUN > 85 mg/dl), and Severe nephropathy ( shorten RBC survival)
  5. Bone marrow conditions - include leukemia, multiple myeloma (cancer of the plasma cells in bone marrow), and lymphoma (blood cancer).
  6. Medical conditions leads to low RBC count include cancer, rheumatoid arthritis, HIV/AIDS.
  7. Nutritional deficiencies such as iron, copper, foliate vitamins B6 and B12 can falsely affect the result.
  8. Medications - chemotherapy drugs, chloramphenicol, hydantoins, quinidine.
  9. Over hydration
  10. Pregnancy

Causes of an increase in erythrocyte (higher A1C)

  1. Cigarette smoking
  2. Congenital heart disease
  3. Dehydration (due to severe diarrhea)
  4. Kidney tumor (renal cell carcinoma)
  5. Low blood oxygen level (hypoxia)
  6. Pulmonary fibrosis
  7. Polycythemia Vera
  8. Medication: Gentamicin, Methyldopa

Once A1C interferences are recognized; choosing an alternative form of testing, such as glycated serum protein testing (fructosamine or glycated albumin) can help assess glycaemia better. Unfortunately, factors affecting the accuracy of HbA1c measurement may not be recognized clinically.

How accurate is A1C test?

The A1C test result accuracy is up to 0.5 percent plus or minus the actual. This means an A1C of 6.0 percent can measure differently as 5.5 to 6.5 percent.

Many people have a question, what does it mean if I have a high A1C and normal blood sugars? Many others, on the other hand, have a question, what does it means if I have normal A1C and high fasting glucose? If you are one among them visit A1C glucose level relationship.

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