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Serum/Plasma Free Cortisol by High-Performance Liquid Chromatography (HPLC)

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

This test measures the amount of cortisol (a hormone produced by your adrenal glands) that is not bound to proteins in your blood, helping assess cortisol levels in your serum or plasma.

Quick summary

["Understanding your free cortisol levels can help diagnose conditions like Cushing’s syndrome or adrenal insufficiency."]

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

Key facts at a glance

LOINC
1631-1
Short code
GH 30M p Ins IV SerPl-mCnc
Synonyms
GH 30M p Ins IV SerPl-mCnc
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 This Test Is Done

Your doctor may order this test if they suspect hormonal imbalances, such as an overproduction or underproduction of cortisol. It can also be used to monitor conditions like Cushing’s disease, adrenal tumors, or to check cortisol levels in people with certain genetic disorders or stress-related issues.

How the Test Works

A small blood sample is taken from a vein in your arm. The sample is then processed to separate free (unbound) cortisol from other substances in the blood. High-performance liquid chromatography (HPLC) is used to measure the precise amount of free cortisol.

Sample Collection and Preparation

The test requires a blood draw, typically done in a doctor’s office or lab. Your blood will be collected into a special tube that separates serum or plasma from blood cells. This sample is then sent to a lab for analysis.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to avoid certain medications or foods that could affect cortisol levels, such as some steroids or caffeine. If you are taking medications, let your healthcare provider know.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Cortisol

Frequently asked questions

What does a high or low free cortisol level mean?
A high level of free cortisol may suggest conditions like Cushing’s syndrome, where your body produces too much cortisol, or certain types of tumors affecting cortisol production. A low level could indicate adrenal insufficiency, where your adrenal glands don’t produce enough cortisol, or other hormonal disorders.
How long will it take to get my results?
Results from this test are typically available within 1 to 3 business days, depending on your lab’s processing time. Your healthcare provider will discuss the results with you during your follow-up visit.
Can I eat or drink anything before this test?
Generally, no special diet or fasting is required for this test. However, if your doctor has specific instructions, follow them to ensure accurate results. Avoid caffeine or certain medications that might affect cortisol levels if advised.
  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