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Cortisol, Peak Concentration (Serum/Plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures the highest level of cortisol, a key stress hormone, in your blood at its natural peak. Cortisol helps regulate metabolism, immune response, and stress reactions.

Quick summary

["Peak cortisol helps assess how your body responds to stress and supports diagnosis of conditions like Cushing’s syndrome or adrenal dysfunction."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
66735-2
Short code
Cortis AM peak SerPl-msCnc
Synonyms
Cortis AM peak SerPl-msCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your doctor may order this test if you have symptoms of hormonal imbalances, such as unexplained weight changes, high blood pressure, or fatigue. It’s also used to evaluate conditions like Cushing’s syndrome or adrenal insufficiency, especially when other tests suggest abnormal cortisol levels.

What to Expect Before the Test

No special preparation is needed for this test. A blood sample will be taken from a vein in your arm, typically in the morning when cortisol levels are highest. You may feel a slight pinch, but it usually doesn’t cause discomfort.

What Happens During the Test?

A healthcare professional will insert a small needle into your arm to draw blood. The sample is then sent to a lab for analysis using a sensitive immunoassay method to measure cortisol concentration.

What the Results Mean

Results are compared to a reference range that reflects typical cortisol levels in healthy individuals. Elevated levels may indicate conditions like Cushing’s syndrome, while very low levels could suggest adrenal problems or medication effects.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Peak Cortisol Level

Frequently asked questions

What does a peak cortisol test measure?
This test measures the highest cortisol concentration in your blood, typically taken in the morning when cortisol naturally peaks due to daily stress cycles. It helps identify whether your cortisol levels are too high or too low over time.
Why is it important to take the blood sample in the morning?
Cortisol follows a natural daily rhythm, peaking in the early morning. Taking the sample then ensures accurate results, as it reflects your body’s natural stress response. Delaying the test could lead to misleadingly low or high readings.
Can stress or medications affect my cortisol levels?
Yes, stress, illness, or certain medications (like steroids) can temporarily alter cortisol levels. If you’re taking medications or have recent stress, your doctor may adjust testing instructions or timing to avoid misleading results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy