THE SIGNIFICANCE OF SERUM CHOLESTEROL IN THYROID DISEASE 1

Abstract

For objective evaluation of thyroid function it has long been necessary to employ indirect meth-ods, of which the most reliable has been the meas-urement of basal metabolism. Although this pro-cedure has proved a valuable aid to diagnosis, its applicability is limited by the fact that it demands cooperation on the part of the patient who is also required to be in a "basal state, " an ideal condi-tion that is not invariably attainable. Moreover, basal metabolism is not specific; variations of oxi-dation are not mediated through the thyroid gland alone. Other objective measures have therefore been sought. The discovery that serum cholesterol was elevated in myxedema and experimental hy-pothyroidism led to the clinical use of cholesterol measurements as a diagnostic aid. Although there proved to be a statistical inverse correlation between serum cholesterol and thyroid activity, in individual cases this relation as well as the correla-tion of cholesterol with basal metabolism were lost. It became evident that cholesterol was no more-probably less-specific than basal metab-olism. Development of precise methods for the meas-urement of the fraction of iodine precipitated from serum with the proteins, SPI, has provided a more nearly specific test for the functional activity of the thyroid gland. This particular fraction of the circulating iodine under ordinary circumstances appears to be composed chiefly of the thyroid hormone (1). In addition it has the advantage over other diagnostic criteria that it is not in-fluenced by subjective factors and other features that interfere with the conduct and interpretation of measurements of basal metabolism. It has per-mitted the detection of disorders of thyroid func-tion in patients who could not be tested by other objective procedures. In spite of these obvious superiorities, experience has proved that SPI is