What is the differential for elevated T3 (with suppressed T4 and normal TSH) in a patient not taking any thyroid hormones?

Female is in her later 40s with surgical oophorectomy taking Sertraline 50 mg daily and prn Trazodone and Lamotrigine. Has some weight loss and fatigue. No goiter nor any signs of hyperthyroidism on exam. Labs: TSH 0.14; TT4 1.6; Free T4 0.4 (normal range 0.8-1.8); free T3 4.6 (2.3-4.2). Repeat labs 4 months later: TSH 0.41; free T4 0.6; TT3 402 (76-181); free T3 8.0. Prolactin 7.2; FSH 2.1; LH 1.7. What can cause these abnormal TFTs?

1 Answer

Mednet Member

Endocrinology · University of Missouri School of Medicine

Answered on

This patient has a low to low normal TSH, with weight loss and fatigue so I would approach this as mild hyperthyroidism, or T3 thyrotoxicosis. Sertraline has been associated with abnormal TFTs, usually an elevated TSH and low T4, not with increased T3 levels.

Assess the patient for any other symptoms of hyperthyroidism. Is she having palpitations? Ask why the labs were done, and if there are any previous labs to compare. Do a good physical exam to assess for thyroid nodules.

The differential diagnosis for this can include a relatively common diagnosis, like early Grave’s disease or an autonomous thyroid nodule. Also, consider the unintentional exogenous intake of thyroid hormone. This could be an OTC supplement or nontraditional medication...

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