ACTH, Plasma
The ACTH, Plasma test measures adrenocorticotropic hormone, the pituitary peptide that drives cortisol secretion. Drawn with simultaneous cortisol in a timed morning sample, it separates ACTH-dependent from ACTH-independent hypercortisolism and distinguishes primary adrenal insufficiency from central causes, guiding the diagnostic algorithm in established cortisol disorders.
1
Biomarkers
Blood (plasma)
Sample
2–4 business days
Turnaround
No (but morning collection is mandatory)
Fasting
What is the ACTH test?
The ACTH, Plasma test measures the concentration of adrenocorticotropic hormone, the pituitary peptide that regulates cortisol secretion. It is ordered to localise the cause of established cortisol excess or deficiency rather than as a first-line screening test. Plasma ACTH is labile, circadian, and highly dependent on timing and handling, so its interpretation requires simultaneous cortisol measurement and attention to pre-analytical detail. Practitioners use ACTH to separate pituitary Cushing disease and ectopic ACTH syndrome (both ACTH-dependent) from adrenal adenoma or carcinoma (ACTH-independent), and to distinguish primary adrenal insufficiency (high ACTH, low cortisol) from central causes (low or normal ACTH, low cortisol). The test is a step in a structured diagnostic algorithm — hypercortisolism must be biochemically confirmed before ACTH is drawn, and adrenal insufficiency is confirmed by dynamic cortisol testing before ACTH guides aetiology.
What does the ACTH test measure?
Adrenocorticotropic hormone is a 39-amino-acid peptide cleaved from pro-opiomelanocortin in corticotroph cells of the anterior pituitary. Its secretion is driven by hypothalamic corticotropin-releasing hormone and follows a pronounced circadian rhythm, peaking in the early morning and reaching a nadir near midnight. ACTH binds melanocortin-2 receptors on adrenal cortical cells, stimulating cortisol synthesis and, to a lesser extent, adrenal androgen production. Cortisol exerts negative feedback on both the pituitary and hypothalamus, forming the central axis of glucocorticoid homeostasis.
Plasma ACTH distinguishes ACTH-dependent from ACTH-independent causes of hypercortisolism and is essential in the work-up of adrenal insufficiency. An elevated ACTH with low cortisol points to primary adrenal failure, while a low or inappropriately normal ACTH with low cortisol suggests secondary (pituitary) or tertiary (hypothalamic) insufficiency. Suppressed ACTH in the setting of hypercortisolism indicates autonomous adrenal production, whereas elevated or non-suppressed ACTH suggests a pituitary or ectopic source.
Why is the ACTH test ordered?
- Localisation of the cause of biochemically confirmed hypercortisolism (Cushing syndrome), to separate ACTH-dependent (pituitary, ectopic) from ACTH-independent (adrenal) sources
- Differential diagnosis of confirmed adrenal insufficiency, distinguishing primary adrenal failure (Addison disease) from secondary or tertiary causes
- Evaluation of an incidentally discovered adrenal mass with features of autonomous cortisol secretion, where suppressed ACTH supports the diagnosis
- Investigation of suspected ectopic ACTH syndrome in patients with features of Cushing syndrome and a known neuroendocrine tumour or occult malignancy
- Monitoring of patients treated for Cushing disease after transsphenoidal surgery, where a detectable ACTH may indicate residual or recurrent disease
- Assessment of suspected congenital adrenal hyperplasia in conjunction with 17-hydroxyprogesterone and cortisol, where ACTH is typically elevated
- Work-up of unexplained hyperpigmentation with suspected primary adrenal insufficiency, as elevated ACTH stimulates melanocortin receptors
- Part of a paired 0800 h cortisol and ACTH sample in the investigation of suspected hypothalamic–pituitary–adrenal axis dysfunction
Sample collection and turnaround
Sample type
Blood (plasma)
Fasting required
No (but morning collection is mandatory)
Collection method
Venipuncture at patient service centre
Turnaround
2–4 business days
Collection notes
Phlebotomy at a Quest draw site. Sample must be collected in the morning (ideally 0800 h) into a chilled EDTA tube, separated promptly, and frozen if not analysed immediately. Record the exact time of collection. Avoid prolonged tourniquet time and patient stress during the draw. ACTH is highly labile; adherence to cold-chain and rapid processing is critical.
Specimen requirements
Minimum 1 mL EDTA plasma, collected into a pre-chilled tube on ice. Separate plasma within 15 minutes and freeze at –20 °C or below if transport is delayed. Note the collection time on the requisition. Reject haemolysed specimens.
What can affect ACTH results?
ACTH follows a circadian rhythm with peak concentrations between 0600 and 0800 h and a nadir near midnight; reference intervals are valid only for morning samples, and timing must be recorded for interpretation.
ACTH is rapidly degraded by proteases at room temperature; plasma must be separated promptly, collected into chilled EDTA tubes, and frozen if not analysed immediately. Poor handling yields falsely low results.
Physical or psychological stress acutely stimulates the hypothalamic–pituitary–adrenal axis, raising ACTH and cortisol. Samples drawn during acute illness or a difficult venepuncture may not reflect the patient's baseline state.
Current or recent glucocorticoid therapy suppresses endogenous ACTH secretion; a careful medication history is essential, and washout may be required to interpret results in suspected adrenal insufficiency.
Haemolysed or lipaemic specimens can interfere with some immunoassays, leading to spuriously low or variable ACTH; grossly abnormal samples should be rejected and redrawn under proper conditions.
What do ACTH results mean?
Elevated
High ACTH with low cortisol indicates primary adrenal insufficiency (Addison disease, congenital adrenal hyperplasia, bilateral adrenal haemorrhage or infarction). High or non-suppressed ACTH with elevated cortisol points to ACTH-dependent Cushing syndrome — pituitary Cushing disease or ectopic ACTH secretion from a neuroendocrine tumour. Further localisation requires pituitary imaging, high-dose dexamethasone suppression, or inferior petrosal sinus sampling.
Normal
A normal ACTH in the context of normal cortisol reflects intact hypothalamic–pituitary–adrenal function. However, a normal or low-normal ACTH with low cortisol is inappropriate and suggests secondary insufficiency; the ACTH response should be brisk when cortisol is low. Normal ACTH with elevated cortisol may be seen in the early stages of pituitary Cushing disease, where values are not yet frankly elevated but fail to suppress appropriately.
Reduced
Suppressed or undetectable ACTH with elevated cortisol indicates ACTH-independent Cushing syndrome, typically an adrenal adenoma or carcinoma; adrenal imaging is the next step. Low ACTH with low cortisol suggests secondary (pituitary) or tertiary (hypothalamic) adrenal insufficiency, which may be due to pituitary disease, hypothalamic dysfunction, or chronic exogenous glucocorticoid use. A cosyntropin stimulation test confirms the insufficiency, and pituitary imaging or further dynamic testing identifies the cause.
Note: ACTH must always be interpreted with a simultaneous cortisol drawn from the same sample, and the time of collection must be recorded. Reference intervals are assay-specific and valid only for morning samples. Pre-analytical errors — delayed separation, warm specimens, haemolysis — are common and can render results uninterpretable. ACTH is a localising test in confirmed cortisol disorders, not a screening test for suspected axis dysfunction.
Frequently asked questions
ACTH is the pituitary hormone that stimulates the adrenal glands to produce cortisol. Cortisol is the screening test; ACTH is drawn simultaneously to determine whether a cortisol abnormality originates in the adrenal glands or the pituitary–hypothalamic axis.
How to access the ACTH test
The ACTH reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Fleseriu M, et al. Consensus on diagnosis and management of Cushing's disease: a guideline update. Lancet Diabetes Endocrinol. (2021)
- Bornstein SR, et al. Diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2016)
- Nieman LK, et al. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2008)
- Raff H, Findling JW. A physiologic approach to diagnosis of the Cushing syndrome. Ann Intern Med. (2003)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.