TRH Test

The TRH test is used to detect thyroid hormone resistance or other thyroid disorders that could not be reliably detected by standard tests.

TRH (thyroid-releasing hormone; produced in the hypothalamus) stimulates the pituitary gland to release TSH (thyroid-stimulating hormone) and prolactin (breast growth and milk secretion are promoted by prolactin).

Indications

  • Evidence of thyroid hormone resistance (hyperstimulability).
  • DD suppressed and decreased TSH (TSHB; TSH, basal; basal TSH).
  • In hyperprolactinemia (in the context of: fertility diagnostics; male libido disorder) – to detect latent hypothyroidism.
  • Confirmation of therapeutic suppression of TSH in thyroid carcinoma.
  • Diagnosis of unclear cases of thyroid dysfunction.

Contraindications

Possible side effects

  • Nausea
  • Dizziness
  • Headache
  • Increased urination
  • Allergic reaction
  • Asthma attack in asthmatics

Symptoms usually persist for only a few minutes.

Material needed

  • Blood serum, taken in the morning before taking the medication.

Preparation of the patient

  • Two blood samples are needed: the first to measure basal TSH concentration (basal TSH value; TSHB), and the second to be taken 30 minutes after the administration of TRH intravenously (stimulation value).

Confounding factors

The following drugs inhibit the increase in TSH levels:

  • Barbiturates
  • Hormones
    • Doaminagonist (bromocriptine)
    • Dopamine
    • Glucocorticoids
    • Levodopa(dopamine precursor)
    • Prolactin inhibitors (bromocriptine, lisuride).
    • Somatostatin – engl: growth hormone inhibiting hormone (GHIH) or somatotropin release-inhibiting factor (SRIF).
  • Morphine
  • X-ray contrast agent
  • Salicylates (acetylsalicylic acid, ASA)

The following drugs increase the increase in TSH levels:

  • Biperiden
  • Chlorpromazine
  • Domperidone
  • Hormones
    • Clomiphene
    • GnRH (gonadotropin releasing hormone)
    • GHRH (growth hormone releasing hormone)
    • Estrogens
    • Prostaglandins
  • Haloperidol
  • Metoclopramide
  • Spironolactone

For these reasons, the affected person should appear for blood sampling in the morning before taking the medication.

Normal values and evaluation of the TRH test

TSH increase after stimulation Assessment
ΔTSH > 2.0 mU/l and TSHmax < 25 mU/l Inconspicuous findings
ΔTSH < 2.0 mU/l
  • Suspected hyperthyroidism (overactive thyroid gland).
  • Secondary hypothyroidism (hypothyroidism) (rare) [TSH ↓/normal; fT3, fT4 ↓]
  • Severe general illness and other disorders that lower TSH.
  • Acromegaly (metabolic disorder with overproduction of growth hormone with gigantism).
  • Cushing’s disease (metabolic disease with increased cortisone secretion).
ΔTSH > 2.0 mU/l andTSHmax > 4.0 and TSHmax < 25 mU/l Latent hypothyroidism* (mild hypothyroidism).
TSHmax > 25 mU/l Hypothyroidism

ΔTSH = TSHstimulated – TSHbasal* There is still no final agreement among experts for the thresholds of latent hypothyroidism!