From the Guidelines
According to the most recent evidence, a low Adrenocorticotropic Hormone (ACTH) level is generally considered to be below 5-10 pg/mL (1-2 pmol/L) 1.
Importance of ACTH Levels
This threshold is crucial in the evaluation of adrenal insufficiency and Cushing's syndrome. Low ACTH levels typically indicate secondary adrenal insufficiency, where the problem originates in the pituitary gland rather than the adrenal glands themselves.
Interpreting ACTH Results
When interpreting ACTH results, it's essential to consider them in the context of cortisol levels and clinical symptoms. For example, low ACTH with low cortisol suggests pituitary dysfunction, while low ACTH with high cortisol may indicate an adrenal tumor producing excess cortisol.
Clinical Considerations
Time of collection is also crucial as ACTH follows a diurnal rhythm with highest levels in the early morning. Blood samples should ideally be collected in the morning, placed on ice immediately, and processed quickly to prevent degradation of the hormone which could lead to falsely low results.
Key Points to Consider
- Low ACTH levels can indicate secondary adrenal insufficiency
- Interpretation of ACTH results should consider cortisol levels and clinical symptoms
- Time of collection and handling of blood samples are critical to avoid falsely low results
- The relationship between ACTH and cortisol can distinguish between primary and secondary adrenal insufficiency 1
From the Research
Definition of Low Adrenocorticotropic Hormone (ACTH) Level
According to the provided studies, there is no direct reference to the Endocrine Society's definition of a low ACTH level. However, the studies provide some information on ACTH levels in different contexts:
- A study from 2 measured plasma ACTH levels in normal subjects and patients with hypothalamo-pituitary disorders, finding basal levels of 23.1 +/- 13.6 pg/ml in young subjects and 17.5 +/- 11.2 pg/ml in elderly subjects.
- The same study found that plasma ACTH levels were less than the detection limit (5 pg/ml) in patients with isolated ACTH deficiency, and less than 10 pg/ml in patients with hypopituitarism.
Diagnostic Criteria for Adrenal Insufficiency
The studies discuss the diagnostic criteria for adrenal insufficiency, including:
- A study from 3 states that low plasma cortisol and normal to low plasma ACTH indicates a pituitary origin for the deficiency.
- A study from 4 investigates the value of basal cortisol level for prediction of adrenal insufficiency, finding that basal cortisol levels ≤100 and ≥450 nmol/L had high diagnostic accuracy.
ACTH Stimulation Test
The studies discuss the use of the ACTH stimulation test for diagnosing adrenal insufficiency:
- A study from 5 summarizes the recent literature evidence on the conduction and interpretation of the ACTH stimulation test for the diagnosis of secondary adrenal insufficiency.
- A study from 6 defines the effective time frame of adequate serum cortisol response to the short standard 250-microg adrenocorticotropic hormone stimulation test after initiation of high-dose glucocorticoid therapy.
Key points to consider:
- The studies provide information on ACTH levels and diagnostic criteria for adrenal insufficiency, but do not directly address the Endocrine Society's definition of a low ACTH level.
- The ACTH stimulation test is a useful tool for diagnosing adrenal insufficiency, but its interpretation requires careful consideration of the clinical context and laboratory results.