Thyroid disease examination

Indicators of Thyroid Dysfunction

Control of thyroid hormone secretion

Thyroxine

Triiodothyronine

Serum TSH

• Its concentration is inversely proportional to the concentration of T₄,
  • assuming normal function of the hypothalamo-pituitary axis reflects the level of T₄,
• significantly increased: primary hypothyroidism,
• sometimes a modified version is produced - it is also possible to find out
• method of first choice when primary hypothyroidism or hyperthyroidism is suspected,
• monitoring T₄ replacement therapy,
• is examined in hypercholesterolemia and hyperprolactinemia.

Functional test with TRH

• Reflects TSH secretion,
• in central hypothyroidism, in TSH-producing tumors.

Total thyroxine (TT4) and free (FT4) in serum

• Indicators of current secretion,
• FT4 indicates the availability of the hormone to the tissue,
• free thyroxine index - FTI.

$FTI={\frac {concentration\ T4\cdot \%T3-Uptake}{100}}\$

• Priority in the treatment of hyperthyroidism, TSH secretion can still be suppressed in the long term.

Serum total (TT3) and free (FT3) triiodothyronine

• High levels of T₃ during thyroxine treatment – ​​autonomous hyperactivity of the gland,
• indication – examination of hyperthyroidism, severity of primary hypothyroidism, differential diagnosis of low TSH values.

Reverse T₃ (RT3)

• Indirect indicator of conversion of T4 to T3,
• investigation of unknown causes of low TT3 or TT4.

Serum Thyroglobulin (TG)

• Indicator of TG release from an active, inflammatory or tumor gland,
• follow-up of patients after thyroidectomy for differentiated ca as a tumor marker - diagnosis of relapse (rising TG).

α-subunit of hCG

• In general, they detect the formation of molecules with this subunit - also TSH.

Calcitonin, serum thyrocalcitonin

• Indicator of secretory activity of C-cells thyroid glands,
• in the diagnosis of medullary tumors.

Thyroid hormone transport disorders

Thyroxine binding globulin (TBG) in serum

• Quantitatively the most significant carrier,
• high values: genetically, during pregnancy, with contraception,
• low concentrations: malnutrition, malabsorption, hepatic synthesis disorders,
• we investigate T3 and T4 values, which do not correlate with the clinical condition.

Prealbumin, transthyretin in serum

• The second most important transmitter.

Binding capacity of transport proteins, T-uptake

• Meaning and indications as for TBG, we saturate the serum sample with a known concentration of T3 and determine the unbound fraction.

Indicators of autoimmune thyroid diseases

Antibodies against thyroperoxidase (Thyreoperoxidase Antibodies, TPOAb)

• Previously described as antimicrosomal,
• reveal the presence of an autoimmune process, a possible risk of dysfunction,
• indication: goiter of unknown etiology, differential diagnosis of hyperthyroidism,
• risk screening after birth.

Thyroglobulin antibodies

• They reveal the autoimmune process, can explain incorrect results of TGB determination,
• monitoring of differentiated carcinomas of the thyroid gland.

Antibodies against TSH receptors

• They can either stimulate or inhibit,
• risk of developing Graves disease, risk of endocrine ophthalmopathy,
• differential diagnosis of hyperthyroidism.

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