ODP490 Levothyroxine Dosing Based on BMI and Different Causes of Hypothyroidism

While several approaches can be used when initiating levothyroxine therapy, it is commonly stated that total levothyroxine dose can be calculated as a function of the person's body weight. 1.6 mcg/kg of body weight. But studies have suggested that other factors must be assessed when trying to calculate a total daily dose. The cause of a patient's hypothyroidism may have an effect on their actual replacement needs. It is not the same to consider a patient with postsurgical hypothyroidism who has had all thyroid tissue completely removed versus Hashimoto's or Radioactive Iodine ablation where some thyroid function may be preserved. It is also important to consider a patient's ideal body weight as studies have shown that ideal body weight rather than actual body weight may be more useful in determining a patient's ultimate levothyroxine requirements. As the prevalence of obesity is increasing in the United States and worldwide, factors such as BMI may start playing a more important role when deciding initiation dosage in these patients. We conducted a retrospective chart review with a total of 260 hypothyroid patients on levothyroxine and with two stable TSH values on the same dose. We divided the patient into three BMI categories. <= 24.9, 25-29.9 and >=30. Patients with BMI <= 24.9 had a levothyroxine mean (SD) dose of 1.5 MCG/KG (0.63), those with a BMI 25-29.9: 1.3MCG/KG (0.44), and those with a BMI >=30: 1.1MCG/KG (0.45). P Value <0. 001. When further subdivided into the cause of hypothyroidism (Hashimoto's, post surgical and radioactive iodine), the effects of BMI on levothyroxine dose seem to also be affected. In postsurgical hypothyroidism, patients with BMI <= 24.9 had a levothyroxine mean (SD) dose of 1.8 MCG/KG (0.47), BMI 25-29.9: 1.5MCG/KG (0.21) and BMI >=30: 1.4MCG/KG (0.38). P Value <0. 001. Patients with Hashimoto's with BMI <= 24.9 had a levothyroxine mean (SD) dose of 1.3 MCG/KG (0.65), BMI 25-29.9: 1.1MCG/KG (0.50) and BMI >=30: 0.9MCG/KG (0.44). P Value <0. 001. In patients with hypothyroidism due to radioactive iodine therapy, the levothyroxine dose for those with BMI <= 24. was 1.4 MCG/KG, BMI 25-29.9: 1.2MCG/KG (0.53) and BMI >=30: 1.2MCG/KG (0.39). P Value 0.883 These results suggest that when initiating levothyroxine therapy, a starting dose of 1.6 MCG/KG is not adequate for all patients and that BMI and cause of hypothyroidism should be considered before making this decision. Presentation: No date and time listed