I am currently taking 150 mcg of synthroid but have been feeling very weak and fatigued. My endo says my TSH is fine at 1.5 and didn’t want to do any other tests. The gp at local clinical decided to run labs on me and came back with the following:

TSH 1.67 (0.40-4.50) mlU/L (third generation)
Free T4 1.7 (0.8-1.8) ng/dl
Total T3 76 (76-181) ng/dl

I think the girl who wrote the lab order made a mistake as she was supposed to order a Total T4 and a Free T3 as well.

Based on these results in looks like I am extremely high in T4 and really low in T3. Would these explain my extreme fatigue and loss of strength?

A free T3 would have been more useful generally than a Total T3 to help determine thyroid signaling. Generally, for mental function, which includes energy, I like to see it between 330 to 420 pg/dL.

However, a Total T3 < 100 ng/dL is significantly low and may indicate suboptimal thyroid signaling. A Total T4 would have been more useful than a Free T4. Free T4 often is not a sensitive indicator of thyroid signaling. A Total T4 will help determine dosing, given how the vast majority of thyroid hormone is in the T4 inactive storage form, and how one is adding exogenous T4. Generally, for mental health, I like seeing a Total T4 between 8 to 12 ug/dL, assuming adequate conversion to T3 – the active thyroid form – and adequate but not excessive thyroid binding proteins in order to have sufficient Free T3. Assuming the brain is functioning properly – a huge assumption – then I prefer seeing the TSH < 1.0 uU/mL for mental health, on the side closer to zero. TSH is produced when the brain determines it does not have enough thyroid hormone. If the brain is functioning properly, then the brain compartmen'ts amount of thyroid hormone and the body compartment's amount of thyroid hormone can match so that TSH also aligns with the body's needs. However, if the brain is not functioning well - as in mental illness, diabetes, nutritional deficiencies - then the brain may not measure thyroid hormone well or be able able produce adequate TSH. Thus TSH can be artificially lower compared to actual thyroid levels. For most adults, a 150 mcg dose of Levothyroxine works well. It is approximately at the sweet spot for dosing. Thus the question is, why is T3 low and why is a person still fatigued as if thyroid hormone replacement is not working? In this case, if Total T4 is between 8.0 to 12.0 ug/dL, then dosing is good enough. If Total T4 is below 8.0 ug/dL, then perhaps absorption is impaired. Heavy proteins, iron, and other food substances can impair T4 binding and absorption, for example. A higher dose may be needed for T4/Levothyroxine to raise Total T4 to the desired range. If Total T4 is good enough, then conversion to T3 may be impaired. For example, if there is an ongoing infection or other cause of excessive immune system inflammatory signaling or similar problems, then T4 can be shunted to Reverse T3 – the waste product pathway for T4. This lowers production of T3 and lowers overall T4 as the body goes into a state of reducing thyroid hormone availability. Excessive thyroid binding proteins may lower Free T3 – as when there is too much estrogen signaling. Deficient thyroid binding proteins – such as when estradiol is too low, or possibly when testosterone is too high – may lower the half-life of T4, thus causing a reduction in T4 and T3 levels. This is where obtaining T4, T3, Free T3, Free T4, and Reverse T3 is useful in determining where the problem may lie, in addition to obtaining information about the other related systems. If thyroid hormone levels are good enough yet one still has a lack of energy, then there are problems with the other systems, one’s metabolism, or nutrition. For example, thyroid hormone requires adequate supplies of the B-vitamins for function, among many other nutrients.