URINARY EXCRETION OF THYROXINE AND TRIIODOTHYRONINE IN DIFFERENT THYROID FUNCTION STATES IN MAN

Abstract

ABSTRACT Urinary thyroxine (T 4 ) and triiodothyronine (T 3 ) have been measured by radioimmunoassay using trapping and separation on small Sephadex® columns. Serum concentrations of total and free T 4 and T 3 and endogenous creatinine clearance was also estimated. In 67 euthyroid controls the 24 h urinary T 4 excretion varied in parallel with age dependent changes in renal function from mean 1788 to 1051 ng. Urinary T 3 also decreased with age from mean 635 to 280 ng/24 h. Mean urinary clearance of T 4 varied from 40.4 to 22.1 ml/min and T 3 clearance from 160 to 107 ml/min parallel with creatinine clearance. The corresponding mean creatinine clearance values varied from 95 to 57 ml/min. In 24 hyperthyroid patients urinary T 4 and T 3 were highly increased, dependent on elevated free hormones in the serum to mean 3505 and 3865 ng/24 h. The corresponding T 4 and T 3 clearance mean values were 16.7 and 90.0 ml/min. In 7 untreated hypothyroid patients very low urinary T 4 and T 3 values were found on average 139 and 60 ng/24 h. Estimation of urinary thyroid hormones can be used for diagnostic purposes but is of limited practical importance. The physiology of thyroid hormone excretion in urine is complex. Both hormones are excreted by glomerular filtration of free hormones including tubular excretion and reabsorption.