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Doc ordered a free T4 and a tsh-3rd generation. Dont I also need a free t3 (liothyronine)?
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Dr. Susan Wingo
Internal Medicine - Endocrinology
In brief: Not usually
For screening purposes, a TSH level by itself leads to the correct diagnosis ~ 98% of the time.
Free T4 can increase this to nearly 100%. Free T3 (liothyronine) is usually not needed unless there is a discrepancy between the other labs and a person's symptoms. Free T3 (liothyronine) is useful in following patients with known hyperthyroidism, and patients taking a combination of T4 & T3 (liothyronine) thyroid hormone.

In brief: Not usually
For screening purposes, a TSH level by itself leads to the correct diagnosis ~ 98% of the time.
Free T4 can increase this to nearly 100%. Free T3 (liothyronine) is usually not needed unless there is a discrepancy between the other labs and a person's symptoms. Free T3 (liothyronine) is useful in following patients with known hyperthyroidism, and patients taking a combination of T4 & T3 (liothyronine) thyroid hormone.
Dr. Susan Wingo
Dr. Susan Wingo
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