GD 1: Sum activity of peripheral type 1 deiodinase (D1).
As can be seen, TSH and fT4 are horizontal and fT3 levels increase with increased GD1 level. Reflecting that increase and decrease of GD1 only affects T3/fT3 values. The green area is the reference range for GD
HER
In the euthyroid state, others and we have observed a considerable interindividual variability in FT4, TSH and their regulatory set points.15 39 40
Diversity:
Possible molecular mechanisms may include either different individual concentrations and affinities of TRs, variations in the distribution of iodothyronine transporters or a polymorphism in the type 2 deiodinase, which in the presence of a homozygous allele weakens the negative feedback of FT4 on TSH in humans.40 41