HbA1c or A1c is the terms usually used for the test to determine the amount of glycated hemoglobin. The test indicates the average blood sugar levels for the past three months. Another abbreviation for glycated hemoglobin is HgbA1c.
Glycation is a chemical bond (the sharing of electrons amongst atoms) between protein and sugar molecules. With hemoglobin this bond occurs without the controlling action of enzymes.
Hemoglobin, abbreviated as Hgb or Hb, is an iron containing protein that is the oxygen transporting component of red blood cells. It is the function of hemoglobin to carry oxygen from the lungs to the rest of the body.
Sugar in the blood attaches to the hemoglobin in red blood cells. The higher the blood-sugar level, the more glucose binds to the hemoglobin. Longer-lasting high blood sugar episodes result in more glycated hemoglobin molecules.
When hemoglobin has bonded with sugar, it remains glycated for the rest of the life of the red blood cell. As the aged cells die off, new cells are produced to replace them. Newer red blood cells are more susceptible to glycation than older cells. Sugar levels on days closer to the test has a greater influence on the test results than in days further from the test. Clinical trials have indicated that HgbA1c shows improvement in as little as 20 days from starting glucose lowering treatment.
Red blood cells have a life-span of up to 120 days (four months), it varies from person to person. Since red blood cells do not undergo glycation at the same time, the A1c test is a weighted average of the red blood cells for three months.
HgbA1c readings are expressed in two units; as a percent (DCCT) or in mmol/mol (IFCC).
IFCC is the acronym for International Federation of Clinical Chemistry and Laboratory Medicine, recommending expressing the molar concentration of glycated hemoglobin with millimoles per mole (mmol/mol). A mole is an amount of a substance that contains a large number (6.022*10^23) of molecules. A millimole is one-thousandth of a mole. The IFCC testing methodology is the international standard for testing hemoglobin A1c.
DCCT is the acronym for Diabetes Control and Complications Trial and from their recommendation, the amount of glycated hemoglobin is given as a percentage. To relate this percentage to an estimated average glucose (eAG) use these formulas for results with a 95% confidence level. Remembering that it is only the estimated average for the past three months.
(HgbA1c[DCCT] X 1,59) - 2,59 = eAG in mmol/L
(HgbA1c[DCCT] X 28,7) - 46,7 = eAG in mg/dl
Hyperthyroidism affects A1c measurements, showing readings higher than the true values.
Vitamin C uses the same mechanism to get into the cells that glucose does. Taking more than 250 mg vitamin C supplement per day affects the accuracy of HgbA1c measurements. Readings may be lower than the true values.
Iodine supplements artificially increases glycated hemoglobin values.
At the time of testing, your blood sugar levels do not affect the HbA1c results, as the test is measuring the average blood glucose for the past three months. The test will be the same whether your blood sugar is high or low at the moment of testing.
The goal for all diabetics is to maintain their HbA1c below 42 mmol/mol or in the 5% range. To become a member of the 5% club, read Blood Sugar 101.
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