Skip to content

Cortisol, Serum (Free Cortisol)

Published: August 9, 2026Updated: August 17, 2026

This test measures the amount of free cortisol, a form of the hormone cortisol, in your blood. Free cortisol is the active, unbound portion that circulates freely in your serum.

Quick summary

["Free cortisol helps regulate metabolism, immune response, and stress reactions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
41407-8
Short code
Cortis Pre ACTH SerPl-mCnc
Synonyms
Cortis Pre ACTH SerPl-mCnc
Category
hormone
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
60
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 healthcare provider may order a free cortisol test to check for conditions affecting your adrenal glands, such as Cushing’s syndrome (overproduction of cortisol) or Addison’s disease (underproduction of cortisol). It can also help diagnose adrenal insufficiency or evaluate symptoms like fatigue, weight changes, or hormonal imbalances.

What to Expect Before the Test

No special preparation is typically needed, but you may be asked to fast for 8–12 hours before the test if your blood is drawn early in the morning, as cortisol levels naturally rise in the morning. Avoid caffeine or stress-inducing activities for a few hours before testing.

How the Test Works

A blood sample is taken from a vein in your arm. The serum (liquid part of blood after clotting) is then analyzed to measure free cortisol levels using an immunoassay method.

What the Results Mean

Results are compared to reference ranges for your age, gender, and health status. Abnormally high or low levels may signal underlying conditions requiring further evaluation, such as hormone disorders or medication side effects.

Reference range

NCBI: ACTH 10-60 pg/mLN/A

Specimen: serum

Typically collected in the morning (8-10 AM). Inform your provider if taking steroid medications.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Cortisol plays a critical role in managing stress, immune function, and metabolism. Abnormal free cortisol levels may indicate adrenal gland dysfunction, pituitary disorders, or other endocrine conditions. Your doctor will interpret results in the context of your symptoms and medical history.

Short name

Free Cortisol

Frequently asked questions

What causes cortisol levels to be tested?
Cortisol levels may be checked if you have symptoms like unexplained weight changes, fatigue, muscle weakness, or frequent infections. It’s also used to diagnose conditions like Cushing’s syndrome, Addison’s disease, or to monitor treatment for hormone-related disorders.
How do I prepare for a cortisol blood test?
If your test is done in the morning, avoid caffeine and stress for a few hours before your appointment. Follow any fasting instructions your doctor provides, but always confirm with them to avoid unnecessary delays.
Can cortisol levels change based on my daily activities?
Yes, cortisol follows a natural daily rhythm, peaking in the morning and dropping at night. Stress, exercise, or illness can temporarily alter levels, so your doctor may consider timing (e.g., morning vs. evening) when interpreting 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 17, 2026. · Read our editorial policy