THE RELATIONSHIP BETWEEN SERUM PROTEIN-BOUND IODINE LEVELS AND URINARY IODINE EXCRETION AND SERUM THYROTROPHIN CONCENTRATIONS IN SUBJECTS FROM AN ENDEMIC GOITRE AREA IN CENTRAL JAVA

Abstract

ABSTRACT Urinary 127I excretion, 24 h thyroid 131I uptake and serum values of thyrotrophin (TSH), triiodothyronine (T3) and protein-bound iodine (PBI) were measured in subjects from an area with severe (Segni) and moderate (Londjong) iodine deficiency. In Segni, 90 non-cretinous subjects and 40 cretins were studied. In both sub-groups from Segni non-compensated iodine deficiency was found. Although iodine excretion in these sub-groups was the same (mean: ± sd, 127I μg per g creatinine; non-cretins 16.9 ± 10.1 and cretins 15.2 ± 8.0) thyroid hormone serum levels were less in the cretins probably due to additional primary thyroid failure. In the subjects (non-cretins plus cretins) from Segni a positive relationship (r=0.39, P < 0.001) was found between urinary 127I excretion and serum PBI. Moreover in the same subjects a negative correlation was found between serum PBI and TSH (r=0.43; P < 0.001) while serum T3 did not correlate with TSH. In the Londjong area (mean ± sd 127I urinary excretion: 41.6 ± 18.6 μg per g creatinine) iodine deficiency appeared to be compensated in 52 subjects studied since mean serum levels of TSH, PBI and T3 were within normal range. No correlation between PBI and serum TSH was found. PBI too did not correlate with iodine excretion despite the fact that 37 subjects excreted less than 48 μg 127I per g creatinine below which value iodine excretion varied in all but one of the studied subjects from Segni. It is suggested on the basis of a difference in the average iodine intake between the groups from Segni and Londjong, that lack of "iodine buffer capacity" of the thyroid gland in the Segni subjects leads to a situation where changes in iodine intake are readily reflected in T4 production resulting in the correlation found between PBI and urinary excretion in this group.