Abstract: Glycosylated haemoglobin (HbA1c) is routinely used test to monitor long term glycaemic control in diabetic patients. It is well known that genetic variants and chemically modified derivatives of haemoglobin can profoundly affect the accuracy of HbA1c measurements. The degree of interference depends on the HbA1c assay method, type & quantum of haemoglobin variant present in a given sample. Here, we report a rare case showing disproportionately high HbA1c value in a 69 years old female patient with carcinoma breast (adenocarcinoma) with hypertension.