CONCENTRATION OF PRECIPITABLE IODINE IN THE SERUM1

As an aid in the diagnosis of disturbed function of the thyroid gland in patients with equivocal clinical symptoms, the measurement of precipita-ble iodine in serum (SPI) can be used only if its range in euthyroid, hypothyroid and hyperthyroid individuals is defined precisely. Winkler (1) pre-sented a chart of serum iodine values in these con-ditions. However, not only precipitable iodines but also total iodines were included, and the latter, due to inclusion of inorganic iodine, may be er-roneously high. Usually this error amounts to from 1.0 to 2.0 gamma per cent, but occasionally gross errors occur after excessive intake of inor-ganic iodine or contamination (2). The normal range of SPI reported by others has been similar to that reported by Winkler, but the maximal vari-ation has not been clearly defined (3-7). Con-tinued study has also revealed that pituitary or adrenal disease, pregnancy, metabolic disturbances accompanied by disturbed serum proteins, and other conditions to be discussed may, in them-selves, be associated with a diminution or increase of the SPI (8-11). To analyze these abnormalities, re-examination was made of the original values of SPI in physio-logically normal individuals and in patients with untreated, unmistakable hypo- and hyperthyroid-ism (Figure 1). In the present series only values for iodine precipitated with serum protein have been used in normal and hyperthyroid persons. The inclusion of total iodines in the euthyroid and hyperthyroid series might give unduly high val-ues owing to the presence of inorganic iodine. In the hypothyroid group, however, some total iodines have been included, because in a certain number of hypothyroid patients only the total iodine was determined prior to therapy. Recently these patients have never stopped thyroid medica-tion for a sufficiently long period to allow measure-ment of the inherent SPI. That these values (