Specific Chemical Tests on Serum

Prior to 1940 tests of thyroid function were dependent on nonspecific procedures that were based on the effects of the thyroid secretion on 

Protein-Bound Iodine and Butanol-Extractable Iodine 

The reasons for briefly discussing PBI techniques in this review are minimal except for the fact that many automated units are still operating and because a PBI determination is sometimes useful in conjunction with other tests in delineating the site of a biosynthetic block in thyroid hormone synthesis. The subject was last reviewed in the series Advances in Clinical Chemistry by Chaney (C6) in 1958, and probably the most recent review is by Acland in 1971 (A4). 

Improvements in the early procedures developed along two main lines, first Ae colorimetric procedure and, second, Ae introduction of automa- 

One of the biggest problems with FBI procedures whether automated or otherwise, has been iodine contamination, both in the patient and the operator, as well as in the environment in which the test is carried out. There are several reviews (A4, Cl, H6) that adequately list the interferences (including iodine in various forms) with FBI procedure. One of the most comprehensive reviews of the artifactual and physiological factors affecting serum FBI in recent years is the publication by Acland (A4). In a recent study on FBI (F2), iodine contamination was found in 17.5% of euthyroid patients, many of whom had clinically feasible FBI levels. As alternative techniques are now available, it is clear that FBI is an unsatisfactory screening procedme for determining thyroid function. 

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