My son has low T4 but normal TSH levels?

[natex90x]

For about the past year my son has had a number of health issues. He's 17 years old, about 230 pounds, depressed, exhausted immediately when he wakes up, has general aches all over his body, and has also been suffering from migraines for about 5 years.

Things have taken a turn for the worse on all fronts the past 2 months, so we wanted to have some blood work done. His PED ordered some bloodwork, standard CBC, CMP, and also a thyroid profile including T4, TSH, Free T4, and Anti-TPO. Everything came back "normal" except for his T4. I'll post the Thyroid levels below, and can offer more results if helpful on other tests.

T4 (Thyroxine) = 5.50  [Reference 6.09-12.23]
TSH = 1.352 [Reference 0.340-5.600]
Free T4 = 0.63 [Reference 0.28-1.64]
Anti-TPO = <.25^2 Reference 0.00-8.90]

Basically my questions are this: Do those references take into account his age/weight, or are they adult standards? His regular T4 being low means what? Are there additional thyroid tests (or others in general) to seek an answer for his issues?

His doctor's response was everything was normal, so we're at an impass now. It's horrible seeing my son feel like this, and we really need answers.

[Super_sally888]

Sounds like he could have metabolic syndrome.

He needs a thorough endocrine workup.

Also recommend that he tries to adopt a low carb diet, which may help on the weight front.  He should also try to undertake regular exercise, even if it is hard.

I hope things can get better for your son.

[Gibbon1]

He should have more than just a thyroid panel.  Testosterone, cortisol, and growth hormone. I read over and over, low growth hormone is often a first sign of pituitary problems. I know from experience that low testosterone will mess you up.  Cortisol at least roughly checks adrenal functions. But I think adrenals are hard to test.

[Red_Star]

Total T4 is less reliable than free T4. The labs i found online for Total T4:

– Under 5 years of age range is 7-15 mcg/dl
– Between 6 and 10 yrs range is 6-13
– Over 10 years and adults: range is 5-12

Low total T4 can suggest hypothyroidism. Also, severe illness or the use of corticosteroids can decrease binding protein levels and the total T4 will be low but this is not due to hypothyroidism. That said, the free T4 is quite low in the range which is never a good sign as most people feel much better mid way or higher in the range.

Other thyroid lab tests that would be worth checking: free T3 (T4 must be converted to T3 to be used by the body/T3 since that is the only hormone the cells use to regulate metabolism) and thyroglobulin antibody (this may be high even is TPOAb is negative). There is also a test called reverse T3 and if this is elevated you can suffer hypothyroid symptoms as it is blocking the action of free T3.

There is also the possibility of central hypothyroidism. Usually this is a TSH below 1.5 mU/L and free T3 (and possibly the free T4 as well) will be below normal.

Also, a clinical sign that is only seen with hypothyroidism is a skin condition called myxedema. While not everyone with hypothyroidism will have this symptom, this symptom is unique to hypothyroidism.  You can look online for the video demo of the myxedema skin pinch test.