Cortisol Blood Test

Q: What does a cortisol blood test measure?

A cortisol blood test measures cortisol, a steroid hormone made by the adrenal glands that helps regulate your stress response. Since cortisol also affects metabolism, blood sugar, immunity, blood pressure, and energy balance—and changes throughout the day—the test helps evaluate how well your HPA axis (stress hormone system) and adrenal function are working.

Q: How do I interpret cortisol results based on time of day?

Cortisol naturally peaks in the morning and declines through the day, so timing matters. General reference ranges include morning (6–8 a.m.) 6–23 µg/dL, afternoon (4–6 p.m.) 3–10 µg/dL, and evening/night <3 µg/dL. Functional medicine often focuses on the daily pattern—high in the morning and low at night—because rhythm disruption can signal stress overload or circadian issues even if a single value looks borderline.

Q: What lifestyle factors can change cortisol levels?

Stress (acute or chronic), poor or irregular sleep, intense exercise (which can temporarily raise cortisol), certain medications (like steroids, birth control pills, and some antidepressants), and diet factors such as caffeine, alcohol, and high sugar intake can all influence cortisol test results. Supporting healthy cortisol often includes stress-management practices, consistent 7–9 hours of sleep, a balanced diet to help maintain stable blood sugar, and moderate consistent exercise.

Q: What tests can help me learn more about Cortisol Blood Test?

The Functional Health Genetic Test delivers over 750 personalized genetic insights across 10 in-depth genetic reports to support whole-body, systems-level health understanding. The Womens Health and Wellness Blood Test translates your results into personalized, actionable guidance. Your healthcare provider can also recommend targeted blood tests based on your specific pathway results and health history to complement your genetic insights with current biomarker data. Medical and Editorial Standards Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims. Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed. Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice. Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.

Last reviewed: May 12, 2026 Last updated: May 12, 2026

Written by: Jay Hastings , CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance. His work has included scaling healthcare startups, leading CLIA lab integrations, and helping expand consumer access to precision health tools.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

Cortisol Blood Test: Understanding the Stress Hormone and Its Impact on Health

The Cortisol Blood Test is an important biomarker included in the PlexusDx Women’s Health & Wellness Blood Test. Cortisol, produced by the adrenal glands, is often referred to as the “stress hormone.” While it plays a vital role in helping the body respond to stress, it also influences many other systems, including metabolism, immunity, cardiovascular health, and energy balance. Because cortisol levels fluctuate naturally throughout the day and rise in response to meals, exercise, or stressful events, measuring this hormone provides valuable insight into overall health and resilience.

What is Cortisol?

Cortisol is a steroid hormone made in the adrenal glands, small structures located on top of each kidney. Its release is controlled by the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the body’s stress response. When the brain perceives stress—physical or emotional—it signals the adrenal glands to release cortisol into the bloodstream. This hormone prioritizes short-term survival functions while temporarily dialing down processes that are not immediately necessary.

Functions of Cortisol in the Body

Although it is often associated with stress, cortisol is essential for everyday health. Its key functions include:

Fight-or-Flight Response: Provides a rapid boost of energy during stressful situations by mobilizing stored glucose.
Metabolism Regulation: Helps the body use carbohydrates, fats, and proteins efficiently for energy.
Blood Sugar Balance: Ensures stable blood glucose levels, especially during fasting or stress.
Blood Pressure Regulation: Supports healthy cardiovascular function by helping control vascular tone.
Anti-Inflammatory Effects: Helps modulate immune response and reduce inflammation.
Circadian Rhythm: Cortisol levels follow a daily pattern—highest in the morning to promote wakefulness and lowest at night to support rest.

Why Measure Cortisol Levels?

Measuring cortisol levels helps evaluate how well the adrenal glands and HPA axis are functioning. Both abnormally high and abnormally low levels may be linked to health concerns. Doctors often recommend cortisol testing for:

Adrenal Disorders: Diagnosing conditions such as Addison’s disease (low cortisol) or Cushing’s syndrome (excess cortisol).
Stress and Fatigue: Assessing whether chronic stress is affecting hormone balance and energy levels.
Metabolic Concerns: Investigating unexplained weight changes, blood sugar imbalances, or insulin resistance.
Immune and Inflammatory Issues: Evaluating whether cortisol imbalances are contributing to weakened immunity or chronic inflammation.
Sleep Disorders: Identifying cortisol rhythm disruptions that may cause insomnia or irregular sleep patterns.

Specimen Collection Method

The PlexusDx Women’s Health & Wellness Blood Test uses a convenient at-home dried blood spot (DBS) collection with an ADX card. This method requires only a simple finger prick, allowing you to collect your sample in minutes and mail it directly to the lab. Results are accurate and reliable, without the need for a clinic visit.

Reference Ranges for Cortisol

Cortisol levels fluctuate throughout the day, so timing of the test matters. General reference ranges are:

Standard Laboratory Ranges (serum values)

Morning (6–8 a.m.): 6 – 23 µg/dL
Afternoon (4–6 p.m.): 3 – 10 µg/dL
Evening/Night: <3 µg/dL

Functional and Optimal Ranges

Functional medicine often emphasizes the pattern of cortisol production rather than a single measurement. Ideally, cortisol should be highest in the morning (to support energy and alertness) and steadily decline throughout the day, reaching its lowest levels at night to allow restful sleep. Deviations from this rhythm can indicate stress overload, adrenal fatigue, or disrupted circadian health.

Symptoms of Low Cortisol

Low cortisol, also known as hypocortisolism, can occur in conditions such as Addison’s disease or chronic adrenal fatigue. Symptoms may include:

Chronic fatigue or weakness
Low blood pressure or dizziness
Unexplained weight loss
Salt cravings
Low blood sugar (hypoglycemia)
Mood changes, such as irritability or depression

Symptoms of High Cortisol

Elevated cortisol levels are commonly linked to prolonged stress or conditions like Cushing’s syndrome. Symptoms may include:

Weight gain, particularly around the abdomen and face
High blood pressure
Elevated blood sugar or insulin resistance
Sleep problems or insomnia
Frequent infections due to suppressed immunity
Mood swings, anxiety, or irritability

Factors That Influence Cortisol Levels

Several lifestyle and health factors can affect cortisol test results:

Stress: Both acute and chronic stress elevate cortisol production.
Sleep: Poor sleep or irregular sleep schedules can disrupt cortisol’s natural rhythm.
Exercise: Intense workouts temporarily increase cortisol, while moderate exercise supports healthy levels.
Medications: Steroids, birth control pills, and some antidepressants can influence cortisol results.
Diet: Caffeine, alcohol, and sugar intake may alter cortisol balance.

Supporting Healthy Cortisol Levels

Balancing cortisol involves both lifestyle and medical strategies:

Stress Management: Meditation, yoga, deep breathing, and mindfulness practices help regulate the HPA axis.
Consistent Sleep: Aim for 7–9 hours of quality sleep to restore natural cortisol rhythm.
Balanced Diet: Include protein, healthy fats, and complex carbs to maintain stable blood sugar and support adrenal health.
Exercise: Favor moderate, consistent physical activity over excessive high-intensity training.
Medical Care: For diagnosed adrenal disorders, treatment may involve hormone replacement or targeted therapies.

Cortisol and Whole-Body Health

Cortisol is much more than just a stress hormone—it is a critical regulator of metabolic health, immunity, cardiovascular balance, and emotional well-being. When cortisol levels are too high or too low, the effects can ripple through multiple systems, causing fatigue, weight changes, mood imbalances, or chronic inflammation. Measuring this biomarker provides a powerful tool for identifying hidden stress patterns and optimizing long-term health.

Why Choose PlexusDx?

The PlexusDx Women’s Health & Wellness Blood Test offers a comprehensive look at hormone health, including cortisol, through a convenient at-home dried blood spot test. With fast and accurate results, you can better understand your body’s stress response, work with your healthcare provider, and make informed choices for your health and wellness journey.

Key Takeaways

Cortisol is a steroid hormone that regulates stress response, metabolism, blood sugar, blood pressure, and immunity.
Levels naturally peak in the morning and decline throughout the day, supporting energy and circadian rhythm.
Both high and low cortisol can contribute to health issues such as fatigue, weight changes, immune dysfunction, and mood disorders.
Functional health emphasizes the daily rhythm of cortisol as much as the absolute level.
The PlexusDx at-home dried blood spot test makes it simple to measure cortisol as part of a complete women’s wellness panel.

By testing cortisol levels with the PlexusDx Women’s Health & Wellness Blood Test, women gain actionable insights into how stress, lifestyle, and adrenal health are shaping their overall well-being. Understanding this key hormone helps empower better choices for energy, resilience, and long-term health.

Frequently Asked Questions About Cortisol Blood Test

What does a cortisol blood test measure?

A cortisol blood test measures cortisol, a steroid hormone made by the adrenal glands that helps regulate your stress response. Since cortisol also affects metabolism, blood sugar, immunity, blood pressure, and energy balance—and changes throughout the day—the test helps evaluate how well your HPA axis (stress hormone system) and adrenal function are working.

How do I interpret cortisol results based on time of day?

Cortisol naturally peaks in the morning and declines through the day, so timing matters. General reference ranges include morning (6–8 a.m.) 6–23 µg/dL, afternoon (4–6 p.m.) 3–10 µg/dL, and evening/night <3 µg/dL. Functional medicine often focuses on the daily pattern—high in the morning and low at night—because rhythm disruption can signal stress overload or circadian issues even if a single value looks borderline.

What lifestyle factors can change cortisol levels?

Stress (acute or chronic), poor or irregular sleep, intense exercise (which can temporarily raise cortisol), certain medications (like steroids, birth control pills, and some antidepressants), and diet factors such as caffeine, alcohol, and high sugar intake can all influence cortisol test results. Supporting healthy cortisol often includes stress-management practices, consistent 7–9 hours of sleep, a balanced diet to help maintain stable blood sugar, and moderate consistent exercise.

What tests can help me learn more about Cortisol Blood Test?

The Functional Health Genetic Test delivers over 750 personalized genetic insights across 10 in-depth genetic reports to support whole-body, systems-level health understanding. The Womens Health and Wellness Blood Test translates your results into personalized, actionable guidance. Your healthcare provider can also recommend targeted blood tests based on your specific pathway results and health history to complement your genetic insights with current biomarker data.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance. References are included at the end of the article when scientific, medical, or health-related claims are discussed.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.