Thyroid lab tests explained in under 150 words

The two (TSH and T4) are opposite of each other – high T4/low TSH or low T4/high TSH – that means that the problem is intrinsic to the thyroid gland (Graves disease or Hashimoto thyroiditis, for example) and the pituitary is trying to control the thyroid by producing more or less TSH. Those are the most common types of thyroid disease – those that are intrinsic, or primary to the thyroid gland itself.

On the other hand, if both TSH and T4 are either low or high – high T4/high TSH or low T4/low TSH – that means that the process is being driven by TSH. Either there’s a pituitary adenoma making a ton of TSH, or the pituitary is not working well for whatever reason (it’s been radiated, or has undergone necrosis) and it’s not making enough TSH.

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