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©2013 UpToDate ® Print Email Patterns of thyroid function tests during assessment of thyroid function Serum TSH Serum Free T4 Serum T3 Assessment Normal hypothalamic-pituitary function Normal Normal Normal Euthyroid Normal Normal or high Normal or high Euthyroid hyperthyroxinemia Normal Normal or low Normal or low Euthyroid hypothyroxinema Normal Low Normal or high Euthyroid: triiodothyronine therapy Normal Low normal or low Normal or high Euthyroid: thyroid extract therapy High Low Normal or low Primary hypothyroidism High Normal Normal Subclinical hypothyroidism Low High or normal High Hyperthyroidism Low Normal Normal Subclinical hyperthyroidism Abnormal hypothalamic-pituitary function Normal or high High High TSH-mediated hyperthyroidism Normal or low* Low or low-normal Low or normal Central hypothyroidism * In central hypothyroidism, serum TSH may be low, normal or slightly high.