Should we treat subclinical hypothyroidism in obese children?

Thyroid function tests are often requested when investigating obese or overweight children. Slightly raised thyrotropin (TSH) with normal free thyroxine—subclinical hypothyroidism (hyperthyrotropinaemia)—is a common finding. An isolated raised thyrotropin is best described as hyperthyrotropinaemia rather than subclinical hypothyroidism and by definition excludes people with clinical symptoms, positive thyroid antibodies, goitre, or associated thyroidal illness.1 2 The adult consensus guideline defines it as a thyrotropin value between the upper limit of the local normal range and 10 mIU/L.1 Paediatric reviews have adopted a similar definition and thresholds.3 Reference ranges vary with the laboratory but are typically 0.45-4.5 mIU/L.1 In paediatric practice, as in adults, thyrotropin >10 mIU/L is potentially indicative of overt hypothyroidism.4

An isolated increase in thyrotropin is more common in overweight children, with a reported prevalence of 7-23% in obese children compared with only 2% in normal weight children.4 5 Thus it is unclear whether raised thyrotropin is a cause or consequence of obesity and whether thyroxine should be used to help manage these children’s weight.