From the Guidelines
The CRH test is a diagnostic procedure that involves administering 1.0 μg/kg of corticotrophin-releasing hormone intravenously to assess the pituitary gland's response, with a cortisol increase of >=20% indicating a positive response, as supported by the most recent guideline from 2024 1.
Overview of the CRH Test
The CRH test is utilized to evaluate disorders of the hypothalamic-pituitary-adrenal (HPA) axis, particularly in differentiating between Cushing's disease and other forms of Cushing's syndrome.
- It involves the administration of synthetic CRH intravenously, typically at a dose of 1.0 μg/kg, as recommended in the 2024 guideline 1.
- Blood samples are collected before and after the injection to measure ACTH and cortisol levels, with the test's sensitivity and specificity supported by recent evidence 1.
Clinical Applications
The CRH test has several clinical applications, including:
- Diagnosing Cushing's disease by identifying an exaggerated ACTH and cortisol response to CRH, as indicated by a >=20% increase in cortisol from baseline 1.
- Distinguishing between primary and secondary adrenal insufficiency, based on the pattern of hormone response to CRH stimulation.
- Evaluating the integrity of the HPA axis in various clinical conditions, with the test's results informing further diagnostic and therapeutic decisions.
Procedure and Preparation
To ensure accurate results, patients should:
- Fast for 8-12 hours before the test, as recommended for other endocrine function tests.
- Avoid stress and other factors that may influence cortisol levels.
- Discontinue medications that affect cortisol levels, under the guidance of a physician, to minimize potential interference with test results. The CRH test is a valuable diagnostic tool in endocrinology, providing insights into the function of the HPA axis and guiding the management of related disorders, as supported by the recent guideline evidence 1.
From the Research
Overview of the CRH Test
- The CRH (Corticotropin-Releasing Hormone) test is used to diagnose and differentiate various endocrine disorders, including Cushing's syndrome, adrenal insufficiency, and pituitary diseases 2, 3, 4, 5, 6.
- The test involves administering a bolus of CRH, usually 100 μg, and measuring the response of adrenocorticotropic hormone (ACTH) and cortisol levels in the blood.
Diagnostic Applications
- The CRH test is used to differentiate Cushing's disease from ectopic ACTH secretion, and to assess autonomous cortisol secretion by the adrenal glands 2, 4, 5.
- It is also used to diagnose pseudo-Cushing's syndrome, adrenal insufficiency, and to characterize the type of secondary adrenal failure due to exogenous administration of glucocorticoids or endogenous overproduction of cortisol by an adrenal adenoma 3, 6.
Test Procedure and Interpretation
- The test is typically performed by administering a bolus of CRH, and measuring ACTH and cortisol levels at baseline and at various time points after administration 2, 4, 5.
- The peak values of ACTH and cortisol, as well as the percentage increases, are used to diagnose and differentiate various endocrine disorders 2, 4, 5.
- The diagnostic accuracy of the CRH test can be affected by various factors, including the dosage and species of CRH used, and the assay method used to measure ACTH levels 5.
Limitations and Controversies
- The CRH test has limitations in diagnosing adrenal insufficiency, with a low sensitivity of 76% and a high specificity of 96% 6.
- The test is not recommended as a second-line test for adrenal insufficiency due to its low sensitivity, and basal cortisol levels are suggested as a first-line test instead 6.