The low levels of serum total-thyroxine frequently seen in the nephrotic syndrome are due to renal hormone-losses.
The hormone is predominantly eliminated in protein-bound form.
There is no distinct correlation between the amount of protein and thyroxine found in the urine. The amount of T4-losses depends on individual factors, i. e. the kind and duration of the specific renal damage and especially the level of T4 in the serum.
The hormonal depots in the serum are diminished by continuous renal T4-losses, but a euthyroid state is guaranteed by a normal concentration of free thyroxine in the patient's serum.
This »buffer-system« has a great capacity, so that even severe hormonal losses may lead to decompensated hypothyroidism only in very few cases.