What Is ACTH Test
Why This Test Is Done
The ACTH test measures the level of Adrenocorticotropic Hormone in the blood. This hormone is released by the pituitary gland and plays a key role in controlling how much cortisol the adrenal glands produce. Doctors order the ACTH test when they suspect that a person may have an imbalance in cortisol levels, either too high or too low.
The test helps diagnose several conditions, including adrenal insufficiency, Cushing’s disease, Addison’s disease, pituitary disorders, and certain types of tumors that affect hormone production. It is also used when a person experiences symptoms such as unexplained fatigue, weight changes, blood pressure problems, or hormonal irregularities. Because cortisol is vital for stress response, immunity, and metabolism, understanding ACTH levels helps doctors see how well the adrenal–pituitary axis is functioning.
In many cases, ACTH is tested alongside cortisol to get a clearer picture. The relationship between these two hormones provides important clues that a standalone test cannot always show.
Biological Role and Functions of ACTH
ACTH is a peptide hormone produced by the anterior pituitary gland. Its main purpose is to stimulate the adrenal cortex to release cortisol, the body’s primary stress hormone. Cortisol plays a wide range of roles in the body, including regulating metabolism, managing blood pressure, supporting immune function, and helping the body respond to physical and emotional stress.
When the brain senses that the body needs more cortisol—such as during illness, injury, stress, or low blood sugar—it signals the pituitary gland to release ACTH. This process is called the hypothalamic–pituitary–adrenal (HPA) axis. Once released, ACTH travels through the bloodstream to the adrenal glands, where it triggers cortisol production.
ACTH also supports the production of other hormones like androgens and has a small role in maintaining the adrenal glands’ health. Because ACTH levels change throughout the day, typically peaking early in the morning, it must be measured at the correct time to get accurate results.
Medical Importance of Measuring This Parameter
Measuring ACTH levels is crucial because hormonal imbalances can cause significant health problems if left untreated. High or low ACTH levels can point to specific diseases affecting the adrenal or pituitary glands. Since these glands control key hormones in the body, even small abnormalities can create major symptoms.
One of the most important uses of the ACTH test is in diagnosing adrenal insufficiency. In this condition, the adrenal glands do not produce enough cortisol. Low cortisol can be dangerous, especially during physical stress, because the body fails to mount a proper response. The ACTH test helps determine whether the problem lies in the adrenal glands or the pituitary gland.
In contrast, high ACTH levels may indicate overproduction caused by a pituitary tumor or an ACTH-secreting tumor located somewhere else in the body. ACTH testing is also essential when evaluating symptoms such as extreme fatigue, sudden weight changes, chronic low blood pressure, or excessive cortisol symptoms such as rapid weight gain or muscle weakness.
Doctors often combine ACTH testing with stimulation or suppression tests to understand how the adrenal glands respond. These paired tests give a more complete view of hormonal balance.
Conditions Diagnosed Using This Test
The ACTH test contributes to diagnosing and understanding several endocrine disorders. Some of the main conditions include:
Addison’s Disease
This condition occurs when the adrenal glands cannot produce enough cortisol. ACTH levels are typically high because the pituitary attempts to stimulate the poorly functioning adrenal glands. Patients experience symptoms such as fatigue, low blood pressure, darkening of the skin, and salt cravings.
Secondary Adrenal Insufficiency
This condition results from low ACTH levels caused by pituitary dysfunction. Because ACTH is low, the adrenal glands do not receive enough stimulation to make cortisol. Symptoms are similar to Addison’s disease but without skin darkening.
Cushing’s Disease
A pituitary tumor produces excess ACTH, leading to very high cortisol levels. Symptoms include weight gain, high blood pressure, muscle weakness, round face, and thinning skin.
Ectopic ACTH Syndrome
Some cancers, such as lung tumors, can produce ACTH outside the pituitary gland. This leads to extremely high ACTH levels and rapid cortisol overproduction. Symptoms worsen quickly and require urgent evaluation.
Congenital Adrenal Hyperplasia (CAH)
Certain forms of CAH affect cortisol production. As a result, ACTH levels increase in an attempt to stimulate the adrenal glands. This condition is often discovered early in life.
Stress-Related Hormonal Changes
Severe stress, illness, or pain may temporarily raise ACTH levels. While this is usually not dangerous, ACTH testing can help evaluate whether stress alone is causing the hormonal fluctuation or if an underlying disorder is present.
Limitations of the Test
Although the ACTH test is valuable, it has several limitations. ACTH is a hormone that breaks down quickly, so the blood sample must be handled carefully, usually chilled or processed immediately. Delays can lead to inaccurate results.
Another limitation is the natural daily variation in ACTH levels. Because levels peak early in the morning and fall significantly later in the day, samples must be collected at the correct time to avoid misinterpretation.
ACTH levels by themselves cannot diagnose a specific disorder. They must be interpreted alongside cortisol levels, the patient’s medical history, symptoms, and sometimes imaging studies. Additional tests, such as the ACTH stimulation test or dexamethasone suppression test, are often needed for a conclusive diagnosis.
Medications, stress, infections, and even small lifestyle factors can influence ACTH levels, complicating interpretation. For these reasons, the ACTH test must always be analyzed in a broader clinical context.
Additional Information
The ACTH test is often part of a comprehensive endocrine evaluation. Individuals with fluctuating symptoms or unclear cortisol patterns may require repeated measurements. Because ACTH responds quickly to stress, some doctors may advise patients to rest before the test or avoid emotional strain.
In some cases, the test can guide long-term treatment decisions, such as adjusting steroid medications or planning surgery for pituitary or adrenal tumors. Monitoring ACTH levels also helps patients who are recovering from adrenal insufficiency after long-term steroid therapy.
Test Preparation
The ACTH test is usually performed early in the morning, typically between 7 AM and 10 AM, when levels are naturally highest. Patients may be asked to avoid strenuous activity, stress, or certain medications before the test. Fasting is not always required, but the doctor may advise depending on the combination of tests being ordered. It is important to inform the healthcare provider about recent steroid use, as this can significantly alter results.
When to See a Doctor
A person should seek medical advice if they experience unexplained fatigue, weight changes, abdominal discomfort, or symptoms that suggest cortisol imbalance. Sudden or severe symptoms such as dizziness, fainting, high blood pressure, or unusual skin changes should also prompt medical evaluation.
Individuals diagnosed with pituitary or adrenal disorders should undergo regular testing to ensure stable hormone levels. Anyone starting or stopping steroid medications should do so under medical supervision and may need follow-up ACTH and cortisol testing.
Sample Type
ACTH is measured using a blood sample drawn from a vein. The sample must be handled quickly and kept cold to preserve the hormone. In some advanced diagnostic settings, repeated samples may be taken throughout the day to measure hormone fluctuations.
Important Word Explanations
- ACTH: A hormone released by the pituitary gland that stimulates cortisol production.
- Cortisol: The main stress hormone responsible for metabolism, blood pressure, and stress response.
- Pituitary Gland: A small gland in the brain that controls many hormones.
- Adrenal Glands: Glands above the kidneys that produce cortisol and other hormones.
- Adrenal Insufficiency: A condition where the adrenal glands cannot produce enough cortisol.
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