TSH, fT3, fT4

Clinical information

The hormones free triiodothyronine (fT3), free thyroxine (fT4), calcitonin and TSH (thyroid stimulating hormone,) are closely involved in the regulation of the human organism via the hypothalamus, pituitary gland and thyroid gland. The binding of TSH to the TSH receptors of the thyroid gland causes the synthesis and secretion of the T3 and T4 hormones. The largest proportion of circulating T3 and T4 is bound. Only free T3 and free T4 are biologically available.

Diagnostics

In primary thyroid overfunction the thyroid gland produces too much T3 and T4, which inhibits the pituitary gland from releasing TSH. The TSH concentration in blood decreases; FT4 and FT3 are borderline high or increased. In secondary thyroid overfunction FT3 and FT4 are increased. The defect lies in the pituitary gland. It may release too much TSH– because of a TSH-producing tumour, which stimulates the thyroid gland to produce more T3 and T4. The cause may also be a thyroid hormone resistance. As well as being caused by disturbances in thyroid hormone regulation, the symptoms of a hyper- or hypothyroidism can also be the result of thyroiditis (inflammation of the thyroid gland).

Alongside the observation of the clinical disease signs, the determination of TSH, fT3 and fT4 concentrations is critical in the diagnostics of thyroid gland diseases.

Selected Products

Method
Parameter
Substrate
Species
RIA
thyroglobulin (TG)
coated tubes (CT); IRMA
antibody-coated
tubes
native
thyroglobulin
RIA
free triiodothyronine (FT3)
coated tubes (CT)
antibody-coated
tubes
triiodothyronine,
human
ELISA
reverse triiodothyronine (RT3)
antibody-coated
microplate wells
RIA
free thyroxine (FT4)
coated tubes (CT)
antibody-coated
tubes
thyroxine,
human
RIA
Turbo thyrotropin (TSH)
coated tubes (CT); IRMA
antibody-coated
tubes
thyrotropin,
human
RIA
calcitonin
coated tubes (CT); IRMA
antibody-coated
tubes
calcitonin,
human
ELISA
calcitonin
antibody-coated
microplate wells
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