What this test measures
Adrenocorticotropic hormone (ACTH) is secreted by the anterior pituitary in response to corticotropin-releasing hormone (CRH) from the hypothalamus. ACTH then stimulates the adrenal cortex to produce cortisol. The system runs on a negative feedback loop — high cortisol switches off ACTH, low cortisol raises it.
Measuring plasma ACTH alongside a cortisol level lets a clinician place a problem at the right level of the hypothalamic-pituitary-adrenal (HPA) axis. ACTH is extremely labile — it must be collected in a pre-chilled EDTA tube, kept on ice, separated within 30 minutes, and frozen for transport.
Why it matters
Cortisol abnormalities (Cushing's syndrome, Addison's disease, secondary adrenal insufficiency from long-term steroid use) cannot be sorted out without an ACTH level. In Cushing's, a suppressed ACTH points to an adrenal tumour while a high or normal ACTH points to a pituitary or ectopic source. In adrenal insufficiency, a very high ACTH with low cortisol indicates primary disease (Addison's — often autoimmune, tuberculous adrenalitis is still relevant in India), while a low ACTH with low cortisol indicates secondary (pituitary) disease.
Long-term oral or even high-dose inhaled steroid use is the most common cause of HPA-axis suppression seen in Indian clinics — patients can have a clinical adrenal crisis on abrupt withdrawal.
How to prepare
Morning sample (between 7 and 9 am) is essential because ACTH has a strong diurnal rhythm — values fall through the day. Avoid stress, exercise and prolonged fasting before the draw. Do not stop oral steroids without medical advice; if a midnight ACTH or low-dose dexamethasone suppression test is part of the workup, follow the specific timing your doctor gives. The tube must be EDTA, pre-chilled and kept on ice — confirm with the collection technician.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| ACTH (pg/mL)[1][2] | 7.2 – 63 pg/mL (morning, ambulatory adult) | Suppressed ACTH with high cortisol = adrenal Cushing's (adrenal adenoma or carcinoma producing cortisol independently). Suppressed ACTH with low cortisol = secondary adrenal insufficiency from pituitary disease or chronic exogenous steroids. | High ACTH with high cortisol = Cushing's disease (pituitary adenoma) or ectopic ACTH syndrome (small-cell lung cancer, carcinoid). High ACTH with low cortisol = primary adrenal insufficiency (Addison's disease) — autoimmune in most cases, but tuberculous adrenalitis is still a consideration in India. |
ACTH + Cortisol — paired interpretation
| ACTH | Cortisol | Likely cause |
|---|---|---|
| Low | High | Adrenal Cushing's (adrenal adenoma / carcinoma) |
| High | High | Cushing's disease (pituitary adenoma) or ectopic ACTH (lung cancer, carcinoid) |
| Low | Low | Secondary adrenal insufficiency — pituitary disease or chronic exogenous steroid use |
| High | Low | Primary adrenal insufficiency (Addison's) — autoimmune, TB adrenalitis, adrenal haemorrhage |
| Normal | Normal | HPA axis intact — look for other causes of symptoms |
Frequently asked questions
Why does ACTH have to be drawn in the morning?
ACTH peaks around 6–8 am and falls 50–80% by evening. An afternoon sample can look "normal" in someone who actually has Cushing's, or "low" in someone perfectly healthy. Morning timing is critical.
Why does my report say "chilled tube — keep on ice"?
ACTH is a peptide that degrades quickly at room temperature. The sample must be collected in a pre-chilled EDTA tube, kept on ice, separated within 30 minutes, and frozen for transport. A poorly handled sample gives falsely low results.
I have been on steroids for asthma — will it affect my ACTH?
Yes. Long-term oral or even high-dose inhaled steroids suppress your own ACTH and cortisol. This is the most common cause of "low ACTH with low cortisol" in Indian clinics. Never stop steroids abruptly — taper with your doctor.
Can ACTH be tested alone?
It almost never is — ACTH is interpreted with a simultaneously drawn cortisol. The pair tells the story; either one alone is hard to make sense of.
My cortisol is high and my ACTH is also high — is that bad?
It points to ACTH-dependent Cushing's — either a pituitary tumour (Cushing's disease) or an ectopic ACTH-secreting tumour. Further workup (high-dose dexamethasone suppression, pituitary MRI, sometimes inferior petrosal sinus sampling) is needed.
Does stress raise ACTH on the day of the test?
Yes — acute pain, severe illness, hypoglycaemia or surgery raise ACTH sharply. For a routine outpatient draw, normal levels of stress (traffic, mild anxiety) do not interfere meaningfully.
What is an ACTH stimulation test?
It is a separate test where synthetic ACTH (cosyntropin/Synacthen) is injected and cortisol measured before and at 30/60 minutes. A poor cortisol rise confirms adrenal insufficiency — useful when a baseline cortisol is borderline.
Related Hormones / Endocrine tests
Tests commonly ordered alongside ADRENOCORTICOTROPIC HORMONE (ACTH), or that help interpret an unexpected result.
Sources & references
- Endocrine Society — Cushing's Syndrome Clinical Practice Guideline · accessed 2026-05-30T00:00:00.000Z
- Endocrine Society — Adrenal Insufficiency Guideline · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — ACTH Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Adrenocorticotropic Hormone · accessed 2026-05-30T00:00:00.000Z
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