Serum total, percentage free fraction and absolute serum free hormone concentration of thyroxine and triiodothyronine were measured in control, pregnant and oral contraceptive useis, together with the daily urinary losses of unconjugated thyroid hormones. Increased urinary losses of both hormones, in particular thyroxine, were apparent in pregnancy and these could not be explained in terms either of an increased filtered load of hormone or the presence of proteinuria. The possible existence of filterable small-molecular weight hormone-binding substances in the urine of pregnant patients is discussed. It is concluded that assay of urinary thyroid hormones during pregnancy is of limited diagnostic value because of overlap with thyrotoxic values. 733

No abstract

Urine unconjugated thyroxine and triiodothyronine concentrations were measured by highly specific assay methods in random urine samples from normal subjects, patients with thyroid disease and euthyroid patients with clinical conditions known to affectin vitro thyroid function tests. Data were standardised by expressing hormone concentrations in terms of the simultaneously determined creatinine concentration. Excretion of both hormones was relatively constant throughout the day in individual subjects. Whereas thyrotoxic patients could be distinguished clearly from normal on the basis either of thyroxine or triiodothyronine concentrations, considerable overlap between normal and hypothyroid values was noted. Values for urine thyroxine in excess of normal were apparent in patients with proteinuria, in pregnancy and in phenytoin-treated subjects and the reasons for this are discussed. Furthermore, many euthyroid patients had trioddothyronine values outside the normal range.It is concluded that measurement of hormone concentrations in random urine specimens is of limited value in assessing thyroid status.