Corticosterone Test · Blood

Your adrenal glands make two main stress hormones: cortisol, which gets most of the attention, and corticosterone, which quietly handles jobs cortisol cannot. While cortisol circulates at 10 to 20 times higher concentrations, corticosterone punches above its weight in your brain, where it accounts for roughly 40% of total active stress hormone activity. That means your nervous system depends on corticosterone far more than a standard cortisol test would suggest.

Corticosterone is not part of routine bloodwork, and most doctors never order it. But for specific conditions, particularly rare enzyme deficiencies that disrupt hormone production, this test provides information no other single marker can. It also appears in advanced steroid profiling panels used to investigate unexplained hypertension, hormonal imbalances, or unusual patterns on standard adrenal testing.

What Corticosterone Does in Your Body

Corticosterone is a 21-carbon steroid hormone built from cholesterol in the outer layer of your adrenal glands (the zona fasciculata). The enzyme 11-beta-hydroxylase converts a precursor molecule into corticosterone in response to ACTH, a signaling hormone released by the pituitary gland in your brain. Corticosterone differs from cortisol by one small chemical feature: it lacks a specific hydroxyl group at the 17th carbon position. That tiny structural difference changes how it moves through your body and what it does when it arrives.

Corticosterone acts on two types of receptors found throughout your body: mineralocorticoid receptors and glucocorticoid receptors. Through these receptors, it plays a dual role in your immune system. During acute stress, it promotes inflammation to help fight threats. Once the threat passes, it dials inflammation back down. Your adrenal glands release corticosterone in roughly hourly pulses, and levels spike after stressful events to help your body recover and stay resilient.

One feature that sets corticosterone apart from cortisol is how your body eliminates it. Corticosterone is excreted into bile and undergoes a recycling loop through your intestines, where gut bacteria transform it into byproducts that get reabsorbed and can influence blood pressure by promoting sodium retention. Cortisol does not follow this path, which means corticosterone has a unique relationship with your gut, your blood pressure, and your electrolyte balance.

17-Alpha-Hydroxylase Deficiency

The condition most directly tied to abnormal corticosterone is 17-alpha-hydroxylase deficiency, a rare inherited disorder of the adrenal glands. In this condition, the enzyme that normally converts precursors into cortisol and sex hormones is missing or defective. Because the body cannot make cortisol, it compensates by overproducing corticosterone and a related precursor called deoxycorticosterone (DOC). Both of these molecules promote sodium retention more aggressively than cortisol does.

The result is a characteristic pattern: high blood pressure, low potassium, and absent or delayed sexual development, all driven by the flood of corticosterone and DOC. Corticosterone measurement is specifically indicated for diagnosing this condition. The diagnostic pattern shows markedly elevated corticosterone alongside decreased or undetectable cortisol. The ratio of corticosterone to cortisol, particularly after an ACTH stimulation test, can even identify carriers who have one copy of the gene variant but no symptoms.

Adrenal Insufficiency and Chronic Stress

Because corticosterone is produced alongside cortisol in the adrenal cortex, conditions that damage or suppress adrenal function (such as Addison's disease) reduce both hormones. Cortisol remains the standard diagnostic marker for adrenal insufficiency, but corticosterone levels track in parallel.

On the other end of the spectrum, chronic stress-related conditions such as chronic fatigue syndrome, fibromyalgia, and post-traumatic stress disorder have been associated with lower-than-expected glucocorticoid output. Researchers believe this may develop after prolonged overactivation of the stress axis, a pattern sometimes called "burnout" of the system that controls cortisol and corticosterone together.

Cardiovascular Risk and Glucocorticoid Excess

Direct outcome studies linking corticosterone levels to cardiovascular events in humans do not exist. The epidemiological evidence for glucocorticoid-related cardiovascular risk comes from cortisol studies, not corticosterone. Because these two hormones share a production pathway and generally move in the same direction, cortisol findings provide relevant context, but they are not direct evidence about corticosterone.

In studies of cortisol (the dominant human glucocorticoid), sustained excess is linked to higher rates of cardiovascular events and death. A 15-year study of 198 people with adrenal tumors found that those with subtle cortisol overproduction had cardiovascular event rates roughly 2.5 to 4 times higher than those with inactive tumors, and survival rates were significantly worse. A separate meta-analysis found that long-term glucocorticoid exposure, measured in hair samples, was associated with meaningfully higher cardiovascular disease risk. Whether corticosterone independently contributes to these outcomes beyond cortisol's effects has not been studied directly.

Reference Ranges

Corticosterone does not have established clinical interpretation tiers the way cortisol, cholesterol, or blood sugar do. No major endocrine society has published diagnostic cutpoints for this hormone. The ranges below come from research studies using modern measurement techniques and represent what healthy people typically show, not proven risk thresholds.

Age and sex are the two most important variables affecting where your level falls. In men, corticosterone tends to decline with age. In women, levels vary with menstrual cycle phase, menopause, and oral contraceptive use. Body weight has a weak negative relationship with levels, and people with abnormal cholesterol ratios tend to have upper reference limits about 10 nmol/L lower than the general healthy population.

Because different labs use different measurement techniques, and inter-laboratory variability for corticosterone is high (median 10% between labs, with over a third of cases exceeding maximum acceptable imprecision), you should always compare results from the same lab over time rather than benchmarking a single result against published ranges.

Tracking Your Trend

A single corticosterone reading tells you very little. The within-person biological variability for this hormone runs roughly 18 to 23%, meaning your level can swing by a fifth from one draw to the next even if nothing has changed in your health. Add in the strong circadian rhythm (levels peak around waking and bottom out at night), hourly pulsatile secretion, and sensitivity to acute stress, and a one-time snapshot is easy to misread.

If you are tracking corticosterone, get your blood drawn at the same time of day each time, ideally between 8:00 and 9:00 AM. Aim for at least two readings on separate days before drawing any conclusions, especially if a result looks borderline. If you are investigating a specific condition or monitoring an intervention, a baseline followed by retesting in 3 to 6 months gives you the trajectory you need. After that, annual checks are reasonable to confirm stability.

When Results Can Be Misleading

Several common situations can shift your corticosterone reading without reflecting a true change in adrenal health. Being aware of these helps you avoid acting on a number that does not represent your baseline.

• Time of day: Corticosterone follows a strong daily rhythm. A sample drawn at 4:00 PM will look very different from one drawn at 8:00 AM, and neither is "wrong." Unstandardized timing is the single most common cause of uninterpretable results.
• Fasting: Skipping meals for 18 hours or more raises corticosterone primarily by slowing how fast your body clears the hormone, not by increasing production. If you fast before a morning draw, your result may be artificially elevated.
• Acute illness or surgery: Severe illness can increase cortisol production up to six-fold, and corticosterone tracks in parallel. After major surgery, levels remain elevated for 72 hours or longer with the normal daily rhythm completely disrupted. Wait at least a week after acute illness before testing.
• Medications that alter steroid metabolism: Azole antifungals (ketoconazole, itraconazole), the anesthetic etomidate, and the drug metyrapone all inhibit the enzyme that produces corticosterone. Drugs that speed up cortisol breakdown (rifampin, carbamazepine, phenytoin, phenobarbital) can lower corticosterone as a side effect. CYP3A4 inhibitors like ritonavir slow breakdown and raise levels. These drugs shift the number without causing adrenal disease.

How Corticosterone Responds to Stimulation and Suppression

One of the most distinctive features of corticosterone is how dramatically it responds to ACTH stimulation compared to cortisol. After an ACTH challenge, corticosterone increases roughly 15-fold, compared to only a 1.4-fold increase for cortisol. This outsized response makes it a potentially more sensitive indicator of subtle changes in adrenal reserve, though this observation comes from research settings and has not been incorporated into clinical guidelines.

After dexamethasone suppression (a test that checks whether the stress axis can be "turned off"), cortisol drops to about 14% of baseline, while corticosterone only drops to about 37%. This means the two hormones do not always move in lockstep, and you cannot reliably infer your corticosterone level from a cortisol result alone.