Abstract

Prof. Dr. R. Balajinathan MD and *Dr. Deepika S. MD.

ABSTRACT

HbA1c is used for screening as well as for diagnosing Diabetes Mellitus. It depends on ambient levels of glycemia over the preceeding 2-3 months but also on the RBC turnover from the bone marrow. HbA1c may not accurately reflect the level of glycemia in conditions of altered erythrocyte turnover, one such condition being hypothyroidism, thereby causing false elevation of HbA1c which can result in false diagnosis of pre diabetes or diabetes mellitus. The aim of this study is to assess changes in HbA1c levels independent of changes in plasma glucose levels after initiation of thyroxine replacement in non diabetic patients with overt hypothyroidism. In these patients the post treatment FBS and PPBS were with normal limits. The HbA1c estimation was done and was found to be increased. The average HbA1c was around 5.83%.This lead to false diagnosis of dysglycemia in 67% of patients. False diagnosis of impaired glucose tolerance -60% and diabetes was 7%. After thyroxine replacement and achievement of euthyroidal state follow up was done for 3 months post achieving euthyroidal state. The T4 and T4 on the average was found to be TSH-3.66 and T4- 7.85 within normal range, although there was no difference in fasting and post prandial blood sugars the mean HbA1c decreased to 5.25%. Therefore in hypothyroid patients diagnosis of pre diabetes or diabetes should only be based on fasting blood glucose and post prandial blood glucose .So we conclude that HbA1c is not a valid test for diagnosis of prediabetes or diabetes in the presence of hypothyroidism.