The diagnostic value of recently developed thyroid function tests

A number of new renal function tests has been developed which permit a simple and efficient diagnostic procedure. T4 determination by the competitive displacement method should be the first test to be applied; PBJ or the T4-RIA may be used as substitutes. If the findings are unclear, this test may be supplemented by the T3 test to determine the thyroxin binding capacity; the free thyroxin index (FTI) is calculated from these two values. Then, if the findings are still unclear or if they differ from the clinical diagnosis, the next test to be used in case of suspected hyperthyroidism is the determination of the T3-RIA to exclude T3 hyperthyroidism. Finally, the TRH test or the radioiodine test might also be used to this purpose. With these tests, practically all cases of hyperthyroidism can be clarified. For course control during therapy, the simple T4 test or, in case of T3 hyperthyroidism, the T3-RIA are most suitable. In case of suspected hypothyroidism, the T4 and T3 tests and the calculation of the free thyroxin index are still the first method to be employed. If the findings are unclear, the TSH value, too, should be determined in addition to the classical parameters Achilles jerk, cholesterol, and CPK. This should be enough in practically all cases. For course control in cases of hypothyroidism, the T4 test, in addition to cholesterol and Achilles jerk time, is greatly recommended. This programme is the most simple and low-cost procedure currently available for diagnostics of the renal function. (orig.)