Effect of Correction of Hyperthyroidism with Anti-thyroid Drugs on the Glycated Hemoglobin in Non-diabetic Patients
Dasari Mani Deepthi1, Suresh Vaikkakara1, Avinash Patil1
1Department of Endocrinology, Sri Venkateswara Institute of Medical Sciences, Tirupati, India.
Insights
Treating hyperthyroidism increases glycated hemoglobin (HbA1c) levels, even without changes in blood glucose. This correction improves the accuracy of HbA1c in reflecting true glycemic control.
Area of Science:
- Endocrinology
- Metabolic Disorders
- Hematology
Background:
- Glycated hemoglobin (HbA1c) reflects average blood glucose over 2-3 months but is influenced by erythrocyte turnover.
- Hyperthyroidism accelerates erythrocyte turnover, potentially leading to falsely low HbA1c readings relative to actual glycemia.
Purpose of the Study:
- To evaluate the effect of medically correcting hyperthyroidism on HbA1c levels.
- To differentiate HbA1c changes from alterations in fasting and post-oral glucose tolerance test (OGTT) plasma glucose.
Main Methods:
- Adults (n=36) with overt hyperthyroidism underwent baseline testing.
- Tests included hemoglobin, reticulocyte percentage, HbA1c, and glucose levels (fasting and 2-hr post-OGTT).
- Measurements were repeated after at least three months of Carbimazole treatment achieving near-normal thyroxin levels.
Main Results:
- Hyperthyroidism correction increased hemoglobin (P=0.004) and HbA1c (P=0.025).
- No significant changes were observed in fasting (P=0.28) or 2-hr post-OGTT glucose (P=0.54).
- The proportion of patients with HbA1c ≥ 5.7% increased (P=0.016), enhancing HbA1c's diagnostic sensitivity for prediabetes from 20% to 50%.
Conclusions:
- Untreated hyperthyroidism leads to falsely low HbA1c values in relation to glycemia.
- Medical management of hyperthyroidism normalizes HbA1c, providing a more accurate reflection of glycemic status.
Background:
Glycated hemoglobin (HbA1c) levels are dependent not only on the average blood glucose levels over the preceding 2 - 3 months but also on the turnover of erythrocytes. Hyperthyroidism is known to be associated with an increase in erythrocyte turnover that may falsely lower the HbA1c in relation to the level of glycemia.
Objectives:
To assess the impact of medical correction of hyperthyroidism on HbA1c, independent of changes in the fasting plasma glucose and 2-hour post-oral glucose tolerance test plasma glucose.
Methods:
Adult patients with overt hyperthyroidism (n = 36) were tested for their hemoglobin, reticulocyte percentage, HbA1c and fasting and post-oral glucose tolerance test (OGTT) 2-hour plasma glucose, both at baseline and following at least three months of near normalization of serum thyroxin on Carbimazole treatment.
Results:
Correction of hyperthyroidism in 36 patients was associated with an increase in the hemoglobin (P = 0.004) and a rise in HbA1c (P = 0.025), even though no significant change was observed in both the fasting (P = 0.28) and post OGTT two-hour plasma glucose (P = 0.54). Also, the proportion of patients with HbA1c ≥ 5.7% rose from 3/36 to 10/36; P = 0.016, while the proportion of patients with either abnormal fasting or abnormal post OGTT 2-hour plasma glucose or both did not show any significant change (P = 0.5). The sensitivity of HbA1c to diagnose prediabetes increased from 20% to 50% post- treatment.
Conclusions:
Glycated hemoglobin is falsely low in relation to glycemia in patients with untreated hyperthyroidism.
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