Why is TSH a poor marker of thyroid function?

[rach7612]

I keep reading online about "dosing by symptoms" and not using TSH. However, TSH is the only lab test I've had that indicated a thyroid problem - my free T4 has always been in the "normal" range. I was diagnosed out of the blue during a routine wellness blood test (first time in my life I had any thyroid hormones tested). However, it's clear to me, I've had thyroid disease since at least age 15. I'm now 25. Feeling exhausted, depressed, moody, cold, and struggling to keep up with everyone else at school and work is normal to me. My friends and family said I was "sensitive", "introverted", "melancholy", etc etc. My energy and mood have always been extremely chaotic, and I was treated for bulimia and given antidepressants at various times.

When I first started synthroid, I was convinced the dose was way too low since I felt so tired and weak. I attributed my weight loss (15 lbs in a month) and anxiety to an eating disorder relapse (my weight loss was intentional but certainly extreme at 5'6'' and 130 lbs to start). Surprise, surprise.. the following blood test showed a TSH of .15, and NORMAL free T4! I was dismayed to have my medication lowered. Although looking back, my thyroid hormones were obviously too high.

A couple months later, my TSH was back up to 6.5.. free T4 still "normal". I would have never recognized or been able to articulate my profound sleepiness and sadness that had taken over to my doctor though since that has always been a personal battle for me. I regained the weight I lost, but attributed that and the mood swings to bulimia, and the tiredness to my poor sleeping and eating habits. When the doctor told me my levels were too low, it all made sense though. I have since read that low thyroid can effect appetite hormones in a way that mimics bulimia. So I am gradually learning how to associate symptoms with "hypo" vs "hyper" - but only by using TSH lab results.

I just don't understand how patients can distinguish and dose until symptoms go away since hypo- and hyper- seem to have similar feelings of exhaustion, moodiness, and appetite irregularity. Plus, all those issues can be cause by so many other lifestyle and health issues other than thyroid. And if my doctor were only treating me based on free T4, I would be considered normal and not be given medication at all. It seems the only thing that has provided insight is my TSH. And yet so many online say to ignore TSH.

I see serious dangers of not adequately treating hypothyroid, but they seem to be more long term risks. Hyperthyroid can cause heart problems at anytime though, which makes it seem more desirable to avoid, medically. Why risk dosing by symptoms and accidentally pushing into hyperthyroid range?

Perhaps I am just very unperceptive when it comes to my body, and my doctor does not run all the tests I suspect he should. However, it seems unreliable to go by symptoms which can be vague or have an undefined source. Do you wait until your labs are normal to dose by symptoms? I was recently diagnosed and am quite frankly shocked at all the controversy surrounding lab tests and the different medications. It's adding an emotional component that I'd be better off without (causing me to feel resentful of my doctor possibly treating me inadequately and mistrustful of online information which I suspect is fueled by various drug companies like Armour and Synthroid or disgruntled patients who may have a more extreme situation than me).

Any thoughts? What labs and/or symptoms do you adjust your medication by? Is it a learned skill?

[Imc2111]

Its a good idea to identify your 4-6 strongest symptoms, and, combined with e Free T3 and T4 as Barb said, to adjust your dose until symptoms dissapear. In my case my symptoms are loss of apetite, irregular sleep, depression and anxiety, hair loss and dry eyes.

[Barb135]

TSH is a pituitary hormone and not really indicative of thyroid function.  The free T3 and Free T4 are the actual thyroid hormones, available for use and are the ones that correlate best with symptoms.  

The ranges for Free T3 and Free T4 are very broad, and many people falling into the bottoms of the ranges, are considered to have a thyroid problem, even though their levels are "normal".  What's "normal" for me, may not be normal for you.

Many people find that adjusting medications so Free T4 is at least mid way in its range, and Free T3 is in the upper 1/3 of its range, is where they feel best.

For many people, on thyroid medication, TSH is pretty much useless.  I use myself as an example:  My TSH stays at < 0.01, but my FT3 and FT4 are rarely even at mid range, I sometimes have hypo symptoms, with the never ending exhaustion and weight issues, topping the list.

Unfortunately, symptoms can "cross over" and apply to either hyper or hypo.  You have to go by both symptoms and labs to make a determination, and while TSH is an "indicator", it should never be used, alone to diagnose or treat thyroid issues.  

Have you been tested for thyroid antibodies to determine if you have either Hashimoto's Thyroiditis or Graves Disease?  These are autoimmune diseases in which the body sees the thyroid as foreign and produces antibodies to attack and destroy it.  

Hashmoto's is most often associated with being hypo and the antibody tests are Thyroid Peroxidase Antibodies (TPOab) and Thyroglobulin Antibodies (TGab).  Graves is most often associated with being hyper and the definitive test for it is Thyroid Stimulating Immunoglobulin (TSI).  

This is a long way from being all the information you need, but others will be along to add to it.