Most FT4 ranges start at 0.6-0.8 and go up to about 1.8. So, I have no doubt that yours is on the floor of the range.
With FT4 that low, we'd expect your TSH to be considerably higher. Low FT4 combined with low TSH usually indicates secondary hypothyroidism, which is actually a pituitary dysfunction. The pituitary doesn't put out enough TSH to stimulate the thyroid to produce FT4.
However, that also depends on what FT3 is doing. Unfortunately, your doctor has ordered total T3, not free T3. FT3 gives much more information. Your TT3 is at 41% of range, which is a little low of the upper half of range guideline.
So, while FT4 is very low, FT3 is holding its own pretty well. This is probably what's keeping your TSH down.
T3U is considered an obsolete test of little value. Despite its name, it's actually an indirect measure of T4.
How do you feel? Do you have hypo symptoms? Are you on thyroid meds?
Did the doctor run any antibody tests?
I have felt awful for a long time all the symptoms of hypo. I have gone to a dr for bio HRT becuz the drs keep telling me Im "normal" and it must be menopause. To the credit of this dr she wants to retest in 30 days and see if the small dose of estrogen will kick start the thyroid. I was just curious if this is the thyroid or pituitary or lack of estrogen. My son has hash and T1D. One endo told me that they watch for Graves in the mothers of T1 diabetes and Hashi
Has your doctor suggested testing antibodies to see if you have Hashi's like your son?
With your FT4 so low, it's very unlikely you have Graves'. Graves' is hyperthyroidism and is characterized by high FT3 and FT4 and very low (usually non-existent) TSH. However, Graves' is also an autoimmune disease, and there is an antibody test for it as well. It wouldn't hurt to test for those, too, since although it sounds like a contradiction in terms, you can have both Hashi's and Graves' antibodies.
I see no problem waiting 30 days to retest, but I'd request those antibody tests at the same time. For Hashi's, they are TPOab (thyroid peroxidase antibodies) and TGab (thyroglobulin antibodies), and for Graves', TSI (thyroid stimulating immunoglobulin). Hashi's runs in families.
Thank you for you time goolarra,
I've never been on thyroid meds.
I wrote those labs down to ask for them.. They did test me one time for antibodies and they were negative except the TGab was <1.0 (range 0.0-0.9) but they said " A low positive is seen in a portion of the asymptomatic population" so I've taken that as normal.
Maybe I've been wrong
I am so grateful to this site and all that you do for us, Bless You
How long ago was the TGab test? It's true that a low positive is seen in a portion ofthe asymptomatic population, and TGab can also be somewhat elevated with other autoimmune diseases. However, by far most of us who have Hashi's are TPOab positive. A few are just TGab positive, and some of us are both. So, it might be worth it to run down all the antibodies just to rule those out. A low positive can also mean the onset of disease.
I went to a private lab Jan 2014 and thats when I finally had the TGab done because no other doctor would run it.
TPOab <6 (range 0-34) Jan 2014
Is that TGab or TPOab? You refer to it as both.
Tests that were done in January 2014
TGab <1.0 (range0.0-0.9)
TPO < 6 (range0-34)
Are they not 2 different tests?
Yes, they're two different tests. TPOab is thyroid peroxidase antibodies. Thyroid peroxidase is the enzyme that catalyzes the synthesis of thyroid hormones. TPOab attack thyroid peroxidase and nothing else. Most people with Hashi's are TPOab positive.
TGab is thyroglobulin antibodies. Thyroglobulin is the protein precursor of the thyroid hormones. TGab attack TG and nothing else. A very few people with Hashi's are only TGab positive, but many of us are both.
Both your tests were negative.. However, it still might be worthwhile to see if the slight elevation has increased, is stable or has gone away.