Printed on 2/13/2026
For informational purposes only. This is not medical advice.
This tool interprets thyroid-stimulating hormone (TSH) and optional free T4 levels to provide a clinical assessment of thyroid function. TSH is the most sensitive initial screening test for thyroid disorders. Combining TSH with free T4 allows differentiation between overt and subclinical conditions, primary and central disorders, and guides further workup.
Formula: Clinical interpretation based on TSH and free T4 reference ranges
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
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Normal TSH is generally 0.4–4.5 mIU/L, though ranges vary slightly by laboratory. Some experts advocate a narrower range of 0.5–2.5 mIU/L. TSH is inversely related to thyroid hormone levels — high TSH means low thyroid function and vice versa.
TSH is the most sensitive indicator of thyroid status because small changes in thyroid hormone levels cause amplified changes in TSH. TSH abnormalities often precede free T4 changes, making it better for detecting early (subclinical) thyroid disease.
Subclinical hypothyroidism: elevated TSH with normal free T4 (affects 4–10% of adults). Subclinical hyperthyroidism: suppressed TSH with normal free T4 (affects 1–2%). Both may progress to overt disease and should be monitored. Treatment depends on TSH level and symptoms.
Medications (levothyroxine, biotin supplements, steroids, lithium), pregnancy (lower TSH in first trimester), time of day (TSH peaks at night), illness (non-thyroidal illness syndrome), and pituitary disorders can all affect TSH. Biotin supplements can falsely alter TSH assays — stop 2 days before testing.