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A chemical (electrical) charge is present on the molecule of HbA1c, and the amount of the charge differs from the charges on the other components of hemoglobin. The molecule of HbA1c also differs in size from the other components. HbA1c may be separated by charge and size from the other hemoglobin A components in blood by a procedure called high pressure (or performance) liquid chromatography (HPLC). HPLC separates mixtures (e.g., blood) into its various components by adding the mixtures to special liquids and passing them under pressure through columns filled with a material that separates the mixture into its different component molecules. Because HbA1c is not affected by short-term fluctuations in blood glucose concentrations, for example, due to meals, blood can be drawn for HbA1c testing without regard to when food was eaten.
"Estimation of blood glucose control in diabetes mellitus"