Fürst mener at barn har en høyere thyreostat, det betyr at TSH stiger fortere hos dem enn hos oss. Altså når ft4 synker hos oss så stiger TSH, og ved barn stiger TSH fortere.
eller en tredje forklaring: Barn vil ha en høy ft4.

Referanse om at de skal ha ft4 i øvre tredel :

http://www.medscape.com/viewarticle/417948_print
helt på slutten av artikkelen
"
Whereas measuring serum FT4 appears to be most practical for assessing thyroid status in patients with central hypothyroidism, the optimal therapeutic range is not clearly elucidated. One group suggested that FT4I (indirect measure of serum FT4) maintained in the upper half of the reference interval and clinical monitoring are sufficient.[7] Previously, our criteria were a normal serum FT4 concentration in combination with TSH below the upper limit of normal.[9] In the present retrospective study, FT4 results were distributed around the middle of the reference interval in combination with a low normal mean TSH. Nevertheless, these FT4 concentrations were significantly lower than those in patients with primary hypothyroidism at our institution.

In children with documented mild central hypothyroidism and short stature, increasing serum FT4 from the lower third to near the upper third of normal during 6 months of levothyroxine therapy significantly increased growth velocity.[22] Withdrawal of levothyroxine resulted in a return to a low growth velocity. These observations provide, at least in children, a justification for targeting FT4 in the upper half of the reference interval, not just in the normal range.

It is difficult to assess what the target FT4 should be in adults. Improvements in biochemical end points after levothyroxine replacement therapy may provide guidance. Examples include serum total cholesterol and low-density lipoprotein in patients with subclinical hypothyroidism,[23] and serum sex hormone- and corticosteroid-binding globulins, fibronectin, and procollagen-III peptide in patients with overt thyroid diseases.[24, 25] Perhaps an optimal target FT4 concentration in adults should be the same as in children, or at least midnormal with associated clinical correlation. Validation of the best approach ultimately requires prospective studies with improved, objective methods for determining clinical thyroid status.
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Angående ft3, så vil kroppen ved begynnede hypothyreose greie å holde ft3 ganske høyt.
Angående tidspunkt for prøver, så er TSH om morgenen dobbelt så høyt eller i det miste en del høyerer enn om ettermiddagen. Grrafer over dette står i lærebøkene.
I 2000 når jeg prøvde å få diagnose, ble min TSH høyst 2,5 men når jeg tok samme prøve to år senere med en noe høyere ft4, så ble TSH 4,5, forsklellen var at den ble nå alltid tatt om morgenen. Så det kan nosk stemme.
Og i www.thyroidmanager.org står det også om dette, og at man kan få en TSH på 7 hvis man blir oppe hele natten før prøven....

Jeg synes en TSH på 5-noe hos et barn er for høy.