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Laboratory & Imaging
Laboratory & Imaging: Thyroid
Laboratory diagnosis of hypothyroidism: Interpretation of test results
The clinical diagnosis is supported by laboratory testing with the ultrasensitive TSH assay. If the TSH is elevated, repeat testing should be done as there may be transient elevations due to non-thyroidal illnesses. After confirming the TSH elevation, a free T4 level is measured, either directly by T4 RIA or estimated by obtaining a total T4 and a T3 resin uptake. Cost determines the choice of methods.
Note: In pregnancy, there may be increased T4 and decreased T3 resin uptake due to an increased production of binding protein, but free T4 and TSH are normal.
The interpretation of test results is presented below:
Adapted from Pinsky LE