The rational use of pituitary stimulation tests

Abstract

Background: Diseases of the pituitary gland can lead to the dysfunction of individual hormonal axes and to the corresponding clinical manifestations. The diagnostic assessment of pituitary function has not yet been standardized.

Methods: The members of the Neuroendocrinology Section and the Pituitary Study Group of the German Society for Endocrinology (Deutsche Gesellschaft für Endokrinologie) prepared outlines of diagnostic methods for the evaluation of each of the pituitary hormonal axes. These outlines were discussed in open session in recent annual meetings of the Section and the Study Group.

Results: For the evaluation of the thyrotropic axis, basal TSH and free T4 usually suffice. For the evaluation of the gonadotropic axis in men, the testosterone level should be measured; if the overall testosterone level is near normal, then calculating the free testosterone level may be additionally useful. In women, an intact menstrual cycle is sufficient proof of normal function. In the absence of regular menstruation, measurement of the basal estradiol and gonadotropin levels aids in the diagnosis of the disturbance. For the evaluation of the adrenocorticotropic axis, the basal cortisol level may be helpful; provocative testing is in many cases necessary for precise characterization. The evaluation of the somato-tropic axis requires provocative testing. Aside from the insulin tolerance test, the GHRH-arginine test has become well established. Reference ranges normed to the body mass index (BMI) are available.

Conclusion: The diagnostic evaluation of pituitary insufficiency should proceed in stepwise fashion, depending on the patient's clinical manifestations and underlying disease. For some pituitary axes, measurement of basal hormone levels suffices; for others, stimulation tests are required. In general, the performance of combined pituitary tests should be viewed with caution.

Figure 1

Hormones of the anterior pituitary lobe, their regulation by hypothalamic peptides, and the hormones of the peripheral endocrine glands that are under their control GHRH, growth-hormone-releasing hormone; CRH, corticotropin-releasing hormone; TRH, thyrotropin-releasing hormone; GnRH, gonadotropin-releasing hormone; GH, growth hormone; IGF-1, insulin-like growth factor 1; PR, prolactin; ACTH, adrenocorticotropic hormone; TSH, thyroid-stimulating hormone; T4, thyroxine; LH, luteinizing hormone; FSH, follicle-stimulating hormone

Figure 2

Structured assessment of basal pituitary hormones followed by evaluation with dynamic testing methods The relevant anterior pituitary axes are shown in the upper portion of the diagram as in Figure 1, while the steps to be followed in endocrinological assessment are shown in the lower portion. CI, contraindications; IGF-1, insulin-like growth factor 1; fT4, free thyroxine; TSH, thyroid-stimulating hormone; LH, luteinizing hormone; FSH, follicle-stimulating hormone; CRH, corticotropin-releasing hormone; ACTH, adrenocorticotropic hormone; IHT, insulin hypoglycemia test; GHRH, growth-hormone-releasing hormone; TRH, thyrotropin-releasing hormone; GnRH, gonadotropin-releasing hormone; SHBG, sex-hormone binding globulin