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Background In normal, euthyroid individuals, 20% of the circulating active thyroid hormone triiodothyronine (T 3 ) comes directly from the thyroid gland and 80% is produced in non-thyroidal tissues by the activation of the inactive prohormone

.2 μIU/ml. However, TSH on admission was low at 0.16 μIU/ml (0.3–4.7), free tri-iodothyronine (FT 3 ) elevated at 1031 pg/dl (249–405), and free thyroxine (FT 4 ) elevated at 5.6 ng/dl (0.8–1.6) ( Fig. 1 ). Pan-cultures returned negative and an 0800 h

conversion of thyroxine (T 4 ) to triiodothyronine (T 3 ) and therefore gaining rapid control of the thyrotoxicosis. However, clinicians need to be aware of the potential adverse drug reactions with high dose PTU treatment and what management options may be

Vestergaard H Nielsen S Christensen SE Seefeldt T Helleberg K Pedersen KM 2007 Sources of circulating 3,5,3′-triiodothyronine in hyperthyroidism estimated after blocking of type 1 and type 2 iodothyronine deiodinases. Journal of

features of primary autoimmune hypothyroidism, who was gradually titrated up with levothyroxine to supraphysiological doses. This eventually led to the normalisation of TSH levels but persistently elevated free triiodothyronine (T3) and thyroxine (T4

nodules with a mildly enlarged thyroid gland. No other abnormalities were found. Investigation Increased fT 4 and free triiodothyronine (fT 3 ) levels were found in the context of unsuppressed TSH levels ( Table 1 ). The determination of fT 4 and

showed a discordant profile with high free T4 (FT4) at 45.7 pmol/L (normal range: 12–22), high free T3 (FT3) at 11.8 pmol/L (normal range: 3.1–6.8) and a TSH 3.19 mIU/L (normal range: 0.27–4.2). Further work up of the proband confirmed a normal alpha

, laboratory tests on routine screening revealed hyperthyroidism: thyrotrophin (TSH) 0.065mIU/L, free thyroxine (fT4) 16.67pmol/L, and free triiodothyronine (fT3) 9.61pmol/L. Methimazole (30mg/day) was administered and the patient was referred to an

(T 4 ) concentration 29.5 pmol/l (reference range 9.0–19.0 pmol/l), TSH concentration 3.672 mU/l (reference range 0.4–4.5 mU/l) and free triiodothyronine (T 3 ) concentration 6.5 nmol/l (reference range 0.9–2.5 nmo/l). This abnormality persisted when

suppressed thyroid-stimulating hormone (TSH) (reference range: 0.3–4.0 mU/L), a free triiodothyronine (T3) of 30.8 pmol/L (reference range: 3.5–6.5 pmol/L) and a free thyroxine (T4) of 62.3 pmol/L (reference range: 9.8–18.8 pmol/L) ( Fig. 1 ). An