Common mistakes around TSH Basis

A common mistake is relying solely on TSH to assess thyroid function. TSH is a pituitary hormone that responds to free T3/T4, but it can be misleading in central hypothyroidism (pituitary/hypothalamic dysfunction) where TSH may be normal or low despite low peripheral hormones. Biotin supplements can artificially lower TSH. Reference ranges vary by age, sex, and ethnicity; a TSH of 2.5 mU/L may be normal for an 80-year-old but borderline for a 30-year-old. Many overlook that TSH alone cannot detect autoimmune thyroiditis (Hashimoto) or subclinical hypothyroidism with normal TSH but elevated antibodies. The diurnal rhythm (TSH peaks in the morning) is often ignored. Conclusion: TSH is a useful but incomplete marker. A full thyroid workup should include free T3, free T4, antibodies (TPO, Tg), and possibly ultrasound. Evidence is based on endocrine guidelines and clinical practice.