The Assay of Urinary Thyroid Hormones for Assessing Thyroid Function

Abstract

A competitive protein binding assay for thyroxine (T-4) and a radioimmunoassay for triiodothyronine (T-3)were applied to determine the urinary concentrations of these hormones.These measurements were shown to offer excellent diagnostic discrimination between euthyroid, hypothyroid, and hyperthyroid subjects. Urinary T-3 and T-4 levels were not affected by changes in the concentration of thyroxine binding globulin (TBG) or by changes in binding capacity; and therefore, remained normal during pregnancy, oestrogen ,and phenytoin therapy. There was no significant circadian variation in urine T-3 excretion. Thus T-3 assays of overnight urine samples could be used in conjunction with dynamic test procedures, such as thyrotrophin (TSH) stimulation test, to enable the rapid assessment of the integrity of the hypothalamic-pituitary-thyroid axis.

Thyroxine in unextracted urine

“…Our data on the values of free T4 in 24-h collec¬ tions of urine evaluated by direct radioimmuno¬ assay in healthy euthyroid subjects (Table 1) Chan (1974) were notably higher than our results. This is probably due to the methods employed.…”

“…Subsequently, sev¬ eral groups developed methods to quantitate T4 in the urine using different procedures (Tal & Sulman 1971;Burke et al 1972;Pérez-Vega et al 1973;Black et al 1973;Ishihara et al 1974;Burke 1974;Chan 1974;Rogowski & Siersbaek-Nielsen 1977;Kolendorf et al 1978;Rogowski et al 1978Rogowski et al , 1980I versen & Pedersen 1979;Faber et al 1981). …”

Effect of Phenytoin Therapy on Thyroid Function

“…Chan, Besser & Landon (1972) recorded a marked increase in urinary thyroxine in one individual following the institution of phenytoin therapy. A subsequent study (Chan, 1974) showed slight but insignificant increases in thyroxine excretion in a group of phenytoin-treated subjects. Chan's (1974) assay method for urine unconjugated thyroxine involved acidification and alcohol extraction of urine-steps which lead to artefactually high estimations (Black, Griffiths, Hoffenberg & Leatherdale, 1973).…”

Assessment of Thyroid Function During Pregnancy

“…Urinary T, and T, levels were measured as described elsewhere (Chan, 1974) and the results expressed as pg. of hormone excreted per 24 hours.…”

“…An alternative approach, involving the calculation of the free thyroxine index (FTI) (Clark and Horn, 1965) has proved unsatisfactory, as it is not proportional to free T, in the second and third trimester (Souma et al, 1973) and it provides us no information about circulating T, which is of equal, if not more, importance. A second indirect approach involves the determination of the urinary excretion of T, and T4 which normally relate closely to circulating free hormone concentrations (Chan and Landon, 1972;Chan et al, 1972;Burke et al, 1972;Chan, 1974;Burke and Shakespeare, 1974). The purpose of the present study was to investigate the conventional serum thyroid function tests with a view to establishing a normal range for each trimester of pregnancy, and to compare the results obtained with the urinary thyroid hormone levels found in nonpregnant euthyroid females.…”