The Constancy of the Serum Precipitable or Protein-Bound Iodine in Healthy Adults

IT has been demonstrated that the level of serum precipitable or protein-bound iodine varies with thyroid activity (1–6). As a result of these studies it is evident that in healthy subjects without disorders of this gland the organic iodine fraction in plasma is usually somewhere between 4 and 8 gamma per cent. It is not known, however, whether or not this serum precipitable or protein-bound iodine value changes from time to time within this range in any euthyroid individual. This possibility cannot be excluded in view of the knowledge that not only the level of thyroid activity but also extra-thyroidal factors may alter the value of the organic iodine fraction in serum (7, 8). The studies herein reported establish, however, the relative constancy of the serum precipitable iodine in healthy young adults, male and female, during a period of several weeks.