Skip to content

Cortisol concentration (overnight serum sample)

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

This test measures the level of cortisol, a hormone produced by your adrenal glands, in your blood after fasting overnight. It helps assess adrenal function and potential issues like Cushing’s syndrome or adrenal insufficiency.

Quick summary

["This test checks your body’s natural cortisol production under resting conditions."]

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

Key facts at a glance

LOINC
97765-2
Short code
Cortis p Dex overnight SerPl-sCnc
Synonyms
Cortis p Dex overnight SerPl-sCnc
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 recommend this test if you have symptoms like unexplained weight gain, fatigue, high blood pressure, or changes in your mood and energy levels. It’s also used to diagnose or monitor conditions affecting your adrenal glands, such as Cushing’s disease or Addison’s disease.

What to Expect Before the Test

You’ll need to fast (not eat or drink anything except water) for 10–12 hours before the test. Your blood will be drawn early in the morning after this overnight fast to get an accurate reading of your cortisol levels.

How the Test Works

A blood sample is taken from a vein in your arm. The sample is collected in the morning after fasting to measure cortisol levels, which naturally rise and fall throughout the day. This overnight fasting helps isolate cortisol production during a low-stress period.

What the Results Mean

Results are compared to standard ranges to determine if your cortisol levels are too high or too low. Abnormal results may indicate hormonal imbalances or other health conditions that require further medical evaluation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Overnight Serum Cortisol

Frequently asked questions

How long does it take to get my results?
Results are typically available within 1–3 business days, depending on your lab’s processing time. Your healthcare provider will discuss the findings with you during your follow-up visit.
What should I do if I feel unwell before my test?
If you experience severe symptoms like dizziness, fainting, or extreme fatigue before your test, contact your doctor immediately. In rare cases, you may need to reschedule or receive temporary adjustments to your treatment.
Can I take medications before this test?
Some medications may affect cortisol levels. Always inform your doctor or lab technician about all medications, supplements, or herbal products you’re taking. They may advise you to stop certain medications temporarily or adjust your schedule.
  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