What is the best initial screening test for suspected hyperthyroidism, typically performed with another test?

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Multiple Choice

What is the best initial screening test for suspected hyperthyroidism, typically performed with another test?

Measuring TSH is the best initial screen for suspected hyperthyroidism because the pituitary gland responds to changes in thyroid hormone levels very quickly, making TSH a highly sensitive indicator of thyroid status. In hyperthyroidism, rising thyroid hormones provide negative feedback that suppresses TSH, often before free T4 (and free T3) become clearly abnormal. So a low or suppressed TSH reliably flags thyrotoxicosis and prompts the next step of checking free T4 (and sometimes free T3) to confirm and assess severity. The other tests serve more in etiologic workup or imaging after screening rather than as first-line screening: free T3 alone can miss some cases, radioactive iodine uptake helps differentiate causes, and thyroid ultrasound assesses anatomy rather than function.

Measuring TSH is the best initial screen for suspected hyperthyroidism because the pituitary gland responds to changes in thyroid hormone levels very quickly, making TSH a highly sensitive indicator of thyroid status. In hyperthyroidism, rising thyroid hormones provide negative feedback that suppresses TSH, often before free T4 (and free T3) become clearly abnormal. So a low or suppressed TSH reliably flags thyrotoxicosis and prompts the next step of checking free T4 (and sometimes free T3) to confirm and assess severity. The other tests serve more in etiologic workup or imaging after screening rather than as first-line screening: free T3 alone can miss some cases, radioactive iodine uptake helps differentiate causes, and thyroid ultrasound assesses anatomy rather than function.

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