<prompt> Glucose is linked to haemoglobin throughN-linkageO-linkageC-C linkageO-H linkage  <response>: When blood glucose enters the erythrocytes, it glycates the e-amino group of lysyl residues and the amino terminals of hemoglobin.The fraction of hemoglobin glycated, normally about 5, is propoionate to blood glucose concentration.Since the half-life of an erythrocyte is typically 60 days, the level of glycated hemoglobin HbA1c reflects the mean blood glucose concentration over the preceding 6 to 8 weeks.Measurement of HbA 1c therefore provides valuable information for management of diabetes mellitus.Enzymatic addition of any sugar to a protein is called glycosylation, while non-enzvmatic process is termed glycation.Interpretation of HbA1C valuesHbA1C valuesInterpretation 5.5 Normal 5.5 - 7 Adequate control 7 - 8 Inadequate control 8 - 9 Poor control Any values between 5.6 and 6 .4 are to be considered as impaired glucose tolerance. Value above 6 .5 is considered as diabetic Harpers illustrated Biochemistry ,30th ed ,page 59 