Levothyroxine therapy adequacy, dose estimation and vitamin D effect assessment in a sample of Iraqi female patients with different causes of hypothyroidism

Abstract

Exogenous levothyroxine dose modulation and euthyroidism achievement is a persistent challenge in clinical settings. This study strives to assess the adequacy of treatment and identify the patients’ factors that can be used to estimate the euthyroid levothyroxine dose. A secondary objective was to assess vitamin D supplementation impact on thyroid status. A review of a prospectively collected information from 142 female patients from Baghdad Center of Nuclear Medicine from June 2019 until March 2020 who were receiving levothyroxine for different causes was done. After a follow-up period, the patients’ thyroid tests were assessed and the euthyroid doses for each cause category were statistically analyzed. Thyroid function was assessed before and after three months of vitamin D supplementation for 29 out of 50 patients who measured its level. Sixty-six patients (47%) of the sample were inadequately replaced. Iatrogenic causes of hypothyroidism were associated with a higher levothyroxine dose than primary hypothyroidism. BMI was the most significant predictor of the euthyroid levothyroxine dose (r=0.601 and p=0.001 in those with total thyroidectomy). The euthyroid dose was also correlated with duration of treatment, and the presence or absence of iron and calcium supplements.Vitamin D supplementation resulted in a significant thyroid-stimulating hormone level decrease (‒3.7 ± 4.7 µIU/ml, P-value= 0.001) without affecting thyroid hormones. BMI can be used to predict a levothyroxine replacement dose that is approximate to that required to achieve euthyroidism. Vitamin D supplementation is associated with TSH reduction in hypothyroid subjects.