Correlation of Levothyroxine Dose with Autoimmune Antibody Titer in Primary Hypothyroidism
The relationship between the level of antithyroid antibodies and the required dose of levothyroxine in substitution for autoimmune hypothyroidism is a poorly explored question. Therefore, a retrospective study of more than 300 patients was conducted, and we bring you a brief summary.
Hypothyroidism − Pathogenesis and Treatment Goals
Hypothyroidism is one of the most common endocrine disorders. In developed countries, the usual cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto's disease). This is characterized by the presence of polyclonal antibodies targeting the thyroid gland, leading to apoptosis of thyroid follicular cells. Serum levels of antithyroid peroxidase antibodies (TPOAb) and antithyroglobulin antibodies (TgAb) often correlate with disease activity.
The main goal of hypothyroidism treatment is the normalization of thyroid-stimulating hormone (TSH) through thyroxine supplementation. Since both insufficient and excessive levels of thyroxine can have adverse tissue impacts, it is essential to administer levothyroxine in an adequate dose. The optimal dose depends on the degree of hypothyroidism, body weight, and age of the patient and is influenced by compliance with the treatment, concurrent medications, or comorbidities.
Several years ago, Turkish authors evaluated the potential correlation between the level of antithyroid antibodies and the daily dose of levothyroxine in patients with overt hypothyroidism.
Study Methodology
This was a retrospective analysis of data from medical records. Included were patients with overt hypothyroidism treated with levothyroxine for at least 1 year and examined at one facility (Fatih Sultan Mehmet Education and Research Hospital in Istanbul) in 2015. All patients were treated according to the same therapeutic standard to achieve a target TSH value of 0.5–4.0 mIU/l. The cutoff values for antibody positivity were 5.6 IU/ml for TPOAb and 4.10 IU/ml for TgAb.
Excluded were patients with liver dysfunction, renal failure, pituitary or hypothalamic disease, secondary hypothyroidism, malabsorption, alcoholism, and pregnant women. The study considered age, gender, body weight, BMI, blood pressure, duration of disease, smoking, and use of proton pump inhibitors.
The daily dose of levothyroxine was calculated as the weekly dose divided by 7. The primary parameter monitored was the average dose of levothyroxine in patients with positive and negative antibody status and the relationship between antibody titers and the required daily dose of the drug.
Results
The population studied included 303 patients (273 women and 30 men) with an average age of 46.6 years. In the group with positive antibodies (n = 210), the average daily dose of levothyroxine was significantly higher than in the group with negative antibodies (n = 93): 78.8 vs. 64.2 mg/day (p = 0.001). In patients with positive antibodies, a small but statistically significant association was found between the level of TPOAb (p < 0.01) and TgAb (p < 0.05) and the dose of levothyroxine.
Conclusion
The titer of antithyroid antibodies, according to findings from this study, positively correlates with a higher dose of levothyroxine administered in the supplementation of autoimmune hypothyroidism. A limitation of the study is the unknown antibody level before the initiation of levothyroxine supplementation.
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Source: Okuroglu N., Ozdemir A., Sertbas Y., Sancak S. The relationship between thyroid antibody titer and levothyroxine dose in patients with overt primary hypothyroidism. Ann Saudi Med 2017; 37 (3): 189−193, doi: 10.5144/0256-4947.2017.189.
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