TRH TEST

Purpose

Pituitary stimulation by TRH in order to measure pituitary production of both TSH and its isolated alpha sub-unit, and to estimate the pituitary stocks of TRH-inducible prolactin. This test also detects TRH receptors on somatotropic cells. Stimulation of these receptors leads to the release of growth hormone (GH) if an adenoma is present (acromegaly) but not if the pituitary gland is functioning normally.

Subject preparation

Fasting and at rest for 30 min.

Product

TRH (Stimu-TSH®, 250 µg vials).

Dose

• Adults: 250 µg.
• Children: 200 µg/m2 body surface area (do not exceed 250 µg).

Protocol

• Samples (dry or EDTA tubes) at time intervals: -15 min (T-15) and 0 (T0).
• Intravenous injection of the correct dose of TRH.
• Samples (dry or EDTA tubes) T+15,T+30, T+60, T+90 and possibly T+120 min after the injection of TRH.

Samples

After centrifugation, draw off the serum or plasma and store at +4°C; freeze the samples for the GH and alpha sub-unit assays.

Assays

TSH and/or the alpha sub-unit and/or GH and/or prolactin.

Side effects

Rare and transient: hot flushes, pins and needles, nausea, headache, dizziness.

Comments

A TRH test can be performed in conjunction with: 

• a LH-RH test (both stimulants injected at the same time).
• an insulin hypoglycaemia test (in which case, it should be carried out in the morning because of the importance of fasting) with or without an arginine test.