Reference values for TSH may be inadequate to define hypothyroidism in persons with morbid obesity: Di@bet.es study.

Abstract

Objective: To analyze the reference range of thyroid-stimulating hormone (TSH) in different BMI catego-ries and its impact on the classification of hypothyroidism.Methods: The study included 3,928 individuals free of thyroid disease (without previous thyroid disease,no interfering medications, TSH <10 mUI/mL and thyroid peroxidase antibodies [TPO Abs] <50 IU/mL)who participated in a national, cross-sectional, population-based study and were representative of theadult population of Spain. Data gathered included clinical and demographic characteristics, physicalexamination, and blood and urine sampling. TSH, free thyroxine, free triiodothyronine, and TPO Ab wereanalyzed by electrochemiluminescence (E170, Roche Diagnostics, Basel, Switzerland).Results: The reference range (p2.5-97.5) for TSH was estimated as 0.6 to 4.8 mUI/mL in the underweightcategory (BMI<20 kg/m 2), 0.6 to 5.5 mUI/mL in the normal-weight category (BMI 20-24.9 kg/m 2), 0.6 to5.5 mUI/mL in the overweight category (BMI 25-29.9 kg/m2 ), 0.5 to 5.9 mUI/mL in the obesity category(BMI 30-39.9 kg/m 2), and 0.7 to 7.5 mUI/mL in the morbid obesity category (BMI 40). By using the refer-ence criteria for the normal-weight population, the prevalence of high TSH levels increased threefold inthe morbid obesity category (P < 0.01).Conclusions: Persons with morbid obesity might be inappropriately classified if the standard ranges ofnormality of TSH for the normal-weight population are applied to them