From the Guidelines
To monitor pituitary function and adrenal glands, the most essential laboratory tests include morning cortisol, ACTH, TSH, free T4, and electrolytes, as recommended by the most recent guidelines 1. When evaluating pituitary function, it is crucial to assess the hypothalamic-pituitary-adrenal axis as a whole.
- Key tests for pituitary assessment include:
- Morning cortisol
- ACTH
- TSH
- Free T4
- Consider evaluating LH, FSH, and testosterone levels in males or estrogen in premenopausal females with fatigue, loss of libido, and mood changes, as suggested by 1.
- For adrenal function, the following tests are recommended:
- Morning cortisol (8 AM)
- ACTH stimulation test for indeterminate results (AM cortisol < 3 mg/dL and < 15 mg/dL) 1
- Basic metabolic panel (Na, K, CO2, and glucose)
- Renin and aldosterone
- Consider adrenal CT for metastasis or hemorrhage in cases of primary adrenal insufficiency 1 It is essential to perform these tests in the morning when hormone levels are at their peak and to avoid glucocorticoids before testing, as they can suppress results. Interpretation of these tests requires consideration of the entire clinical picture, taking into account the integrated system of the hypothalamic-pituitary-adrenal axis and its feedback loops that regulate hormone production 1. Multiple measurements may be necessary to establish patterns, particularly for hormones with diurnal variation like cortisol. In cases where primary adrenal insufficiency is suspected, evaluating for precipitating causes of crisis, such as infection, and performing an adrenal CT for metastasis or hemorrhage, is crucial 1.
From the Research
Laboratory Tests for Pituitary and Adrenal Gland Function
To monitor pituitary (hypophysis) function and adrenal gland function, several laboratory tests can be employed. These tests are crucial for diagnosing and managing disorders related to these glands. The key tests include:
- Insulin Tolerance Test (ITT)
- Low-dose Adrenocorticotrophic Hormone (ACTH) stimulation test
- Glucagon Stimulation Test (GST)
- Short Synacthen Test (SST)
- Corticotropin-Releasing Hormone (CRH) test
- Metyrapone test
Tests for Adrenal Insufficiency
For evaluating adrenal insufficiency, the following tests are used:
- ITT is considered the gold standard but is cumbersome and sometimes contraindicated 2, 3.
- Low-dose ACTH stimulation test is a sensitive and safe alternative to ITT 2, 3.
- GST can also evaluate both the hypothalamo-pituitary-adrenal (HPA) and growth hormone (GH)-IGF-1 axes 2.
- SST, particularly with a low dose, can be used but may not identify all cases of adrenal insufficiency 3, 4.
- CRH test can be used, especially when other tests are contraindicated or inconclusive 3.
Baseline Cortisol Levels
Baseline morning cortisol levels can predict pituitary-adrenal reserve, with assay-specific thresholds proposed for different immunoassays 5. This approach can potentially obviate the need for dynamic testing in some patients.
Combined Tests for Hypothalamic-Pituitary Function
In growth-retarded children treated with growth hormone, combined tests assessing the secretion of LH, FSH, TSH, prolactin, and ACTH can provide comprehensive information about hypothalamic-pituitary function 6. These tests help in identifying patients with persistent GH deficiency and those with additional disturbances of the hypothalamic-pituitary axis.
Comparison of Provocative Tests
Different provocative tests have been compared for their diagnostic sensitivity, specificity, and accuracy in evaluating the HPA axis in patients with hypothalamo-pituitary disorders 4. The choice of test depends on the clinical context, availability, and patient-specific factors, with ITT remaining a reference test when feasible.