Cortisol Test
Also known as: Serum Cortisol, Hydrocortisone
What is Cortisol?
Cortisol is a stress hormone produced by the adrenal glands. It regulates metabolism, immune response, and helps the body respond to stress.[MedlinePlus (NIH)]
What This Test Measures
This test measures cortisol levels in blood, urine, or saliva. Levels follow a daily pattern, highest in the morning.[Mayo Clinic]
Why It's Important
Cortisol testing helps diagnose Cushing syndrome (excess cortisol) and Addison disease (cortisol deficiency).[MedlinePlus (NIH)]
Chronic high cortisol affects metabolism, immune function, mood, and cardiovascular health.[Cleveland Clinic]
Who Should Get This Test?
Cortisol testing helps diagnose adrenal disorders.
Risk Factors
- Symptoms of Cushing syndrome (weight gain, purple stretch marks, moon face)
- Symptoms of Addison disease (fatigue, weight loss, low blood pressure)
- Pituitary disorders
- Long-term steroid use or recent withdrawal
- Unexplained high blood pressure or diabetes
- Muscle weakness and bone loss
- Adrenal masses found incidentally
- Severe fatigue unresponsive to rest
Screening Schedule
Not routine; ordered when adrenal or pituitary disorders are suspected. Multiple tests at different times may be needed.
What Happens During the Test
A blood sample is drawn from a vein, typically in the morning (8 AM) when cortisol is highest. Evening and midnight samples may also be collected. Salivary and urinary cortisol tests are alternatives.
Duration
5-10 minutes for blood draw; results typically available within 1 day
Discomfort Level
Minimal discomfort from needle insertion
Risks & Side Effects
Standard blood draw with minimal risks.
- •Brief pain at needle site
- •Small bruise may develop
- •Rare: lightheadedness
- •Very rare: infection at puncture site
Normal Range
Morning (8 AM): 6-23 mcg/dL. Evening (4 PM): 3-15 mcg/dL.
Note: Levels vary by time of day, stress, and testing method.
Source: MedlinePlus (NIH)Unit Conversion
Convert between mcg/dL and nmol/L
| mcg/dL | nmol/L |
|---|---|
| 5 | 138 |
| 10 | 276 |
| 15 | 414 |
| 20 | 552 |
| 25 | 690 |
High Values
High cortisol (Cushing syndrome) causes weight gain, high blood pressure, diabetes, and muscle weakness. Causes include pituitary tumors, adrenal tumors, and steroid medications.[Mayo Clinic]
Low Values
Low cortisol (Addison disease) causes fatigue, weakness, low blood pressure, and salt cravings. It can be life-threatening during stress.[Mayo Clinic]
Test Limitations & Accuracy
Cortisol testing requires careful interpretation:
- ⚠Single random cortisol has limited diagnostic value
- ⚠Cortisol varies significantly throughout the day (diurnal rhythm)
- ⚠Stress, illness, and exercise acutely elevate cortisol
- ⚠Pregnancy and estrogen-containing medications raise cortisol-binding globulin
- ⚠Night shift workers have altered cortisol patterns
- ⚠Some assays have cross-reactivity with synthetic steroids
- ⚠Multiple tests often needed to confirm diagnosis
Alternative & Complementary Tests
Cortisol evaluation often requires multiple tests:
Measures total daily cortisol output; good for Cushing screening
Screens for Cushing syndrome; elevated levels indicate lack of normal evening suppression
Distinguishes pituitary vs adrenal causes of cortisol abnormalities
Confirms Cushing syndrome; cortisol should suppress with dexamethasone
Diagnoses adrenal insufficiency; cortisol should rise after ACTH injection
Test Preparation
Morning tests should be done at 8 AM. Evening tests at 4 PM. Avoid stress before testing.[Cleveland Clinic]
References
Medical Disclaimer
This information is for educational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for interpretation of test results and medical decisions.
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