Medical management of central hypothyroidism is controversial due to lack of reference for evaluation of pituitary negative feedback. Therefore, titration of medical treatment is based on T4 levels, measured with variable laboratory methods. Patients who have central hypothyroidism usually have concomitant deficiencies in other pituitary hormones for which they need replacement therapy such as steroids, testosterone and growth hormone. This combined hormone deficiency makes clinical and laboratory evaluation challenging among these patients. Symptomatically, central hypothyroidism is relatively mild and lack non-specific and it might be overlooked due to other hormonal deficiencies. Replacement therapy for central hypothyroidism is titrated by arbitrary target free T4 levels of above 50th percentile of normal. The goal of our study is to compare the standard results from well known measure methods to a new method for measuring Ft4 using Liquid chromatography - tandem mass spectrometry.

Inclusion Criteria:

• Clinical evidence of central hypothyroidism: status post pituitary surgery and/or radiotherapy plus laboratory documentation of central hypothyroidism, with or without concurrent hormonal deficiencies in other axes, such as ACTH, LH, FSH

Exclusion Criteria:

• Primary hypothyroidism