Total thyroxine (T4)


The review is needed in the suspected diagnosis of hyper- or hypothyroidism.


T4 is the main hormone secreted by the thyroid, the free form is the only active.

Total thyroxine (T4)Technique:

Blood Sample EDTA (ethylene diamine tetra-acetic acid).

radioimmunoassay or enzyme immunoassay.


They went in 1-3 days.

Normal values:

from 45 to 110 mcg / L, 60 to 140 mol / L.

(Conversion factors: ug x 1.29 = nmol; nmol x = 0.77 mcg.)

Pathological changes:

the rate is:

– Increased in hyperthyroidism accompanying low levels of TSH;

– Lowered in hypothyroidism with an elevated TSH.

If hypothalamic-pituitary reached, the TSH is normal.



Practical advice:

Beware of medications that can interfere with thyroid function as antithyroid, Lugol, lithium, but also those containing thyroid hormones and iodine.


Editor-in-chief of the Medical Actu website; general practitioner graduated from the Faculty of Medicine of Algiers in 2005 currently practicing as a liberal.

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