Serum Thyrotropin In Primary Hypothyroidism: A Reliable And Accurate Predictor Of Optimal Daily Levothyroxine Dose

Abstract

To assess the reliability and accuracy of the predicted optimal daily levothyroxine (LT4) dose based on pretreatment serum thyrotropin (thyroid-stimulating hormone or TSH) level in primary hypothyroidism. We examined the relationships between the actual daily LT4 dose required to attain and maintain normal serum TSH concentration and the calculated daily LT4 dose, based on previously established correlations with pretreatment serum TSH concentrations, in 108 consecutive patients with primary hypothyroidism treated in an endocrinology clinic during an 18-month period. Highly significant correlations were noted between the optimal daily LT4 dose and the calculated dose based on either logarithmic regression (r = 0.86; P<0.00001) or linear regression (r = 0.83; P<0.00001). Moreover, the actual mean daily LT4 dose (133 +/- 4 mg) approximated the mean doses predicted by both regression analyses (129 +/- 5 mg and 126 +/- 5 mg, respectively) and was identical in many of the study subjects. The predicted optimal daily LT4 dose based on pretreatment serum TSH level provides a reliable and accurate approximation of the final optimal LT4 dose in patients with primary hypothyroidism and therefore may be a more convenient and cost-effective therapeutic approach than the current traditional clinical practice.