Free T4 low and Tsh normal

[debbiegreco]

my regular Dr who has lowered my synthroid from 100 - 75 and then to 50 based on just tsh was on vacation and the Dr I saw ordered free T4 to be tested too. My tsh this time was in range .91 ( .04-.4.50 but free T 4 was .5 (.08-1.8 She upped my synthoid back to 75 but said just to take it Monday - Friday and retest in 2 months

Not sure what free T4 is and how it relates to TSH and why is there such a wide variation in normal for TSH?

[greygoose]

TSH is Thyroid Stimulating Hormone, produced by the pituitary when it senses that your thyroid hormones are low in the blood. The higher the TSH, the more hypo you are, the lower your thyroid hormones.

FT4 is a thyroid hormone - it's what you're taking, Synthroid is T4. It's a storage hormone that needs to be converted into the active hormone T3. But, you need to have a high enough level to convert. Your FT4 was very low - below range! And, in my opinion, your doctor was much too conservative in just increasing it five days a week. I doubt that will raise it very much.

There isn't a wide variation in 'normal' for TSH. Doctors just think there is. A truly 'normal' TSH, in someone who has no thyroid problems, is around 1. However, once you are on thyroid hormone replacement (levo), the TSH becomes irrelevant, and doctors should not be using it to dose by. It's the FT4 and FT3 that is important.