We analyzed the relation of pretreatment anthropometric measures and serum thyrotropin (TSH) with the levothyroxine requirement. Children (3–18 years) brought to endocrine clinic with newly diagnosed acquired primary hypothyroidism were enrolled consecutively and prospectively with follow-up (July 2014 to April 2016). Children were started on levothyroxine, and dose was adjusted at regular intervals until achieved euthyroidism (serum TSH 0.4 to 4.5 mIU/L). The relationship of age, gender, height, weight, and serum TSH with levothyroxine dose was analyzed by univariate and multivariate regression analysis. Data of 51 children (42 girls and 9 boys) was used for the analysis. Age, weight, height, and serum TSH had significant correlation with levothyroxine daily dose based on weight (D/W) and dose based on BSA (D/BSA). Log10 TSH and gender explained ∼60% absolute levothyroxine daily requirement. The final model built with height and serum TSH predicted ∼85% of D/W and ∼80% of D/BSA.
Conclusion: Pretreatment height and serum TSH can be used to determine levothyroxine dose needed to achieve euthyroidism in a newly diagnosed acquired primary hypothyroidism in children. What is Known: • The starting dose of levothyroxine is currently recommended based on the age of children. What is New: • In pediatric population, the effect of age on levothyroxine daily dose requirements can be explained by pretreatment height. • Pretreatment serum TSH level is an important predictor of levothyroxine daily dose in children with newly diagnosed primary hypothyroidism.