13 yo son--slightly inc. TPOab, low fT4 (BJ?)

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Hi,

I've not posted in a long time, I have been feeling good on 2 grains NT,

although just got test results and my TSH is 0.037 :-O but frees look OK.

I periodically test my son due to family history and all previous tests his

TPOab have been below the limit. Now they are slightly elevated.

And his fT4 is low.

Thyroid Peroxidase (TPO) Ab006676 28 0-20 IU/mL

TSH

2.3 0.450-4.500 uIU/mL

Triiodothyronine,Free,Serum

4 2.3-5.0 pg/mL

T4,Free(Direct)

1 0.93-1.60 ng/dL

Question: The TPOab are barely elevated. How high do they have to be to cause

problems?

The only thing that seems awry is the fT4 which is only 10.45% of the range.

His fT3 looks good.

Can such a low fT4 cause symptoms even if fT3 looks good?

All his friends now have the deep voices and secondary sexual characteristics

starting, and they are much bigger than him. He's small and very thin. He's

been fatigued lately and irritable, seems to need more sleep than most. I also

had a metabolic panel done that I though had ferritin, but I was mistaken.

Any thoughts? His labs do not seem bad enough to be the cause of his symptoms.