Are there any interactions between replacement hormones?
- Because GH therapy can decrease circulating free T 4 levels in adults with GH deficiency, free T 4 should be measured 6 weeks after initiation of GH replacement and after each dose escalation to rule out a mild case of central hypothyroidism.
- This also applies to those patients with central hypothyroidism already receiving LT 4 who are being started on GH therapy.
- Patients with GH deficiency have increased activity of 11-beta hydroxysteroid dehydrogenase type 1, resulting in increased conversion of cortisone to cortisol.
- Thus, GH replacement, by decreasing the conversion of cortisone to cortisol, may expose occult central adrenal insufficiency in patients with borderline ACTH reserve or those receiving subtherapeutic doses of glucocorticoids.
- Gonadal steroids influence GH-mediated hepatic IGF-1 generation. Because oral estrogens decrease IGF-1 levels, women on estrogen replacement therapy need higher doses of GH to reach their target IGF-1 concentrations.
- Commencement of glucocorticoid replacement therapy can unmask central diabetes insipidus.
- Finally, because thyroid hormone increases the metabolic clearance rate of cortisol, initiating LT 4 in patients with coexistent but unrecognized adrenal insufficiency can precipitate an adrenal crisis.
