Which test is commonly ordered to investigate thyroid disease?

Which test is commonly ordered to investigate thyroid disease?

• A. T3
• B. T4
• C. TSH
• D. TRH

Answer: (C)

The TSH test is the best first step when investigating thyroid problems because it is the most sensitive indicator of how the thyroid axis is functioning. The pituitary gland senses circulating thyroid hormones and adjusts TSH levels accordingly: if the thyroid isn’t producing enough hormone, TSH rises to stimulate it; if there’s too much hormone, TSH falls. This feedback makes TSH abnormal earlier than changes in the actual thyroid hormones (T3 and T4) are always detectable, so it’s the most reliable initial screening tool. If TSH is off, clinicians usually check free T4 to confirm and characterize the issue. T3 can remain normal even in some thyroid diseases, and TRH testing isn’t used routinely in clinical practice, which is why TSH is the commonly ordered test.

The TSH test is the best first step when investigating thyroid problems because it is the most sensitive indicator of how the thyroid axis is functioning. The pituitary gland senses circulating thyroid hormones and adjusts TSH levels accordingly: if the thyroid isn’t producing enough hormone, TSH rises to stimulate it; if there’s too much hormone, TSH falls. This feedback makes TSH abnormal earlier than changes in the actual thyroid hormones (T3 and T4) are always detectable, so it’s the most reliable initial screening tool. If TSH is off, clinicians usually check free T4 to confirm and characterize the issue. T3 can remain normal even in some thyroid diseases, and TRH testing isn’t used routinely in clinical practice, which is why TSH is the commonly ordered test.