Usually, the first indicated examination is the determination of the thyrostimulant hormone (TSH), which is produced by the pituitary and acts on the thyroid by stimulating the release of the hormones T3 and T4 in the bloodstream.
The dosage of TSH is commonly considered the most accurate examination to analyze the activity of the thyroid gland. The test allows you to identify situations of hypothyroidism and hyperthyroidism:
- if the TSH is reduced, it means that the liver is working too much (hyperthyroidism);
- otherwise, if it has high values, the thyroid is working too little (hypothyroidism).
In addition, this examination is useful for screening for hypothyroidism in newborns and for monitoring thyroid replacement therapy.
If the TSH level is abnormal, your doctor will prescribe a dosage of total T4 and/or free T4, to confirm the suspected diagnosis. In addition to this determination, the dosage of total or free T3 may also be required.
Other laboratory tests
Other analyses to explain possible thyroid dysfunction include:
- Thyroid antibodies: their assessment helps to distinguish different types of thyroid and to identify autoimmune thyroid diseases;
- Calcitonin: allows you to determine the cause of ofa hypercalcemia.
Only in some particular cases, to understand if there are anomalies, more complex laboratory tests are carried out, such as the TRH test (also known as TSH stimulation tests).
If the results of the laboratory tests show incorrect values, then the endocrinologist will be able to deepen the evaluation by prescribing one or more instrumental examinations, including ultrasound, scintigraphy with a radioisotope (radioiodine or technetium 99m pertechnetate) and agoaspirato.
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|Normal thyroid values|
|Thyroxine (T4) total (TT4)||60 – 150 nmol/L|
|Free Thyroxin (T4) (fT4)||10 – 25 pmol/L|
|Triiodotironine (T3) total (TT3)||1.1 – 2.6 nmol/L|
|Free Triiodothyronine (T3) (fT3)||3.0 – 8.0 pmol/L|
|Tire-stimulant hormone (or thyrotropin) (TSH)||0.15 – 3.5 mU/L|
NOTE: Normal ranges can vary from laboratory to laboratory; In addition, different units of measurement (e.g. mcg/dl and ng/dl) are sometimes used: in this case, the numerical values are completely different from those listed.
High Values – Causes
- Hormone T3 (triiodothyronine) and T4 (tiroxine): if the dosage result is higher than average values (generally for both hormones) it means that the person probably suffers from hyperthyroidism, the most common form of which is Basedow-Graves disease. In other cases, hyperthyroidism can be caused by nodules in the thyroid.
- FT3 and FT4: If their value is higher than usual, it means that the person suffers from hyperthyroidism.
- TSH or hormone thyrotropic: generally, its value is altered and is very high when the person suffers from hypothyroidism.
Low Values – Causes
- Hormone T3 (triiodothyronine) and T4 (thyroxine): if the result is lower than average values, it is probably hypothyroidism, that is, a reduction in the function of the thyroid, with deficient production of hormones. Often, however, the values turn out to be in the norm even if you suffer from hypothyroidism. In any case, this disease may be present from birth, but it can also begin in adulthood or may be due to Hashimoto’s thyroiditis.
- FT3 and FT4: If their value is lower than usual, it means that the person suffers from hypothyroidism.
- TSH or thyrotropic hormone: a meager value indicates the presence of hyperthyroidism.