1. Lab error.
2. A reference range is where 95% of the normal population falls within. Your FT3 level might just be normal for you.
3. Elevated FT3 only can be seen with a condition called T3 toxicosis however your symptoms don't point in that direction.
4. Your symptoms may be due to anaemia so rule that out as a cause.
5. Over conversion of T4 to T3. Tests you could request include TBG (thyroid binding globulin), testosterone, insulin. I never had elevated testosterone myself with insulin resistance though.
Milwaukee Thyroid - 6 Patterns Of Hypothyroidism...
"Pattern 4: Over Conversion
Pattern 4 is the opposite of pattern 3. The thyroid and pituitary are again working properly, but this time there is too much T4 converted to T3 (remember roughly 20% of T4 is conversted into reverse T3 which is inactive and excreted). High levels of testosterone is the cause which also has the added effect of decreasing the amount of thyroid binding globulin (TBG: the taxi that carries the thyroid hormones).
The high levels of T3 in conjunction with low TBG causes cells to become resistant to T3. They close the doors and do not allow anymore T3 into the cells. TSH levels will be normal even though the patient is showing signs of hypothyroidism.
This pattern is similar to insulin resistance. In fact, patients with thyroid over conversion often also present with insulin resistance and polycystic ovary syndrome (PCOS) which is also caused by increased testosterone levels. Managing blood sugar is extremely important. Since there is already to much T3, prescription thyroid medication will not help in this pattern."
Thank your for your reply!
I think a lab error can be ruled out. As I wrote above, my doctor did another test only three days later and the FT3 level was still elevated. It was normal a year ago, though. It's not actually that high, so I thought it might be an insignificant aberrance but my doctor seemed to think that the combination of high FT3 and normal FT4 is weird. My TSH level has been checked several times over the last year and it was slightly elevated sometimes (2.7, 3.05, 3.45), which according to my doctor pointed to possible hypothyreosis.
I had anemia last year and took iron supplements for six months. My iron levels were ok two weeks ago but my doctor said that I might need supplements again in a few months, since my levels are dropping again. (They are still well within the normal range, only my ferritin level has dropped from 59 in march to 27 in june. So I guess that can't be the cause of my symptoms since the levels are still fine.
The text says that over conversion is caused by high testesterone levels... but I guess I would have other symptoms then as well?
I will read a bit more about the things you wrote. Thank you! :)
Symptoms of high testosterone in women include hair loss; excess hair growth on the chin, face, abdomen and chest; acne; disturbances in their menstrual cycle.
Your ferritin is too low in the range. Research has shown that in people with chronic fatigue, iron supplementation increased energy dramatically in people with a ferritin under 50 mcg/L who were not anaemic.
I found this as well about high FT3...
"Even having a high Free T3 due to adrenal or iron problems can be the beginning of too much RT3." - Reverse T3 (also called Reverse Triiodothyronine).
Excerpt from Denver Naturopathic Clinic - Subject: The Normal Range used for interpreting thyroid tests misses many cases of hypothyroid disease...
"In 2002 the American Association of Clinical Endocrinologists suggested that the upper range for a normal TSH be lowered to 3.0. According to the National Association of Clinical Biochemistry, “ In the future, it is likely that the upper limit of the serum TSH euthyroid reference range will be reduced to 2.5 because >95% of rigorously screened normal euthyroid volunteers have serum TSH values between 0.4 and 2.5 ”"