Cortisol (Blood)

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Auckland Te Toka Tumai

Test Guide

Cortisol (Blood)

Testing Laboratory

Auckland Te Toka Tumai | Auckland Hospital

Department

Chemical Pathology

Delphic Registration Code (Alpha Code)

COR

Test Code (Numeric Code)

3006

Laboratory Handling

Phlebotomy

Rapid serum cortisol (Adrenal Catheter placement):
- These must be arranged with the Section Head of Automation, Chemical Pathology, LabPlus (ext 22118, or contact via LabLink ext 22000) at least one day before the catheter placement procedure.
- The turnaround time is approximately 35 minutes from receipt of the sample.
- Hand deliver samples to ensure no transport delays.

Synacthen and dexamethasone tests:
- Pre-synacthen or pre-dexamethasone samples: request " cortisol ". Send immediately.
- Post-synacthen sample: Use separate form and request "post-synacthen cortisol" . Send in a separate bag
- Post-dexamethasone sample: Use separate form and request "post-dexamethasone cortisol". Send in a separate bag

Transport

Rapid serum cortisol: Hand deliver samples to ensure no transport delays.

Registration

Cortisol (Plain, Heparin, EDTA): Timed specimens require separate numbers.
Treat Rapid serum cortisol requests as orange forms and hand deliver at each step of the process.
The yellow form must accompany the specimen throughout the process.

Test Adds Requirement

Lablink: Note requirements under Specimen Collection in regards to arranging this test request. Please refer calls related to these samples to the Automation Section Leader or a Technical Specialist so that the correct tracking form can be filled out.

Sample Stability

24 hours at 20-25°C, 4 days at 2-8°C, 12 months at -20°C

Associated Tests

Synonyms

Hydrocortisone

Turnaround Time

3 hours

Specimen Type

Plasma
Serum

Specimen Requirements

Tube/Container Type:

Preferred

Lithium Heparin PST- Gel (Light Green Cap)

Acceptable

EDTA (Lavender Cap)
Lithium Heparin - Non-gel (Green Cap)
Plain (Red Top)
SST II (Gold Cap)

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

3.5

No of Samples Required

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

Lithium Heparin PST- Gel (Light Green Cap)

Acceptable

Plain (Red Top)

Preferred Sample Volume (ml)

0.5

Minimum Sample Volume (ml)

0.5

Pre-testing Requirements

See Phlebotomy section.

Additional Specimen Information

0.5 mL Paediatric Microtainer PST Blood (Preferred)
0.5 mL Paediatric Microtainer Plain Blood

Diagnostic Use

Cortisol testing may be helpful to assess the status of the HPA axis, however there are limitations in the acute/tertiary setting:

Steroid suppression – It is not uncommon for a patient to receive a dose of corticosteroid as an inpatient, especially in ED if the underlying diagnosis is still not known. Depending on the dose and steroid, it is possible for cortisol to be suppressed for two or more days after a dose. Prolonged use of steroid medications (or use of long half-life steroids, e.g. intra-articular) can result in much longer suppression (at least weeks).
Diurnal variation – At its physiological trough level, cortisol is about half the value of its peak level (in early morning). This introduces variation to the expected results, especially if there is sleep disturbance.
Unrelated pathology – Cortisol secretion may be increased in response to acute illness/stress that is unrelated to the underlying illness.

Therefore random or early morning cortisol measurements are of limited value in the hospital setting. Appropriate stimulation or suppression tests are usually necessary to determine the status of the HPA axis. A very low cortisol can still be useful if hypocortisolism is suspected.

Screening tests for Cushing syndrome:

24 hour urine cortisol
Bedtime urine cortisol/creatinine ratio
Bedtime plasma cortisol
Bedtime salivary cortisol
Overnight low-dose dexamethasone suppression test

Interpretation

Low serum cortisol:
- Consider the non-pathological explanations listed in ‘Diagnostic Use’ above.
- Consider ACTH testing to help differentiate adrenal disease/recent discontinuation of long-term steroids (high ACTH expected) vs. pituitary disease/steroid suppression (low ACTH expected).
- Synacthen stimulation testing may be useful in this context.
High serum cortisol:
- Genuine non-iatrogenic Cushing syndrome is quite uncommon. In most cases, suspicion should be confirmed by at least two positive screening tests for hypercortisolism, e.g. 24hr urine cortisol and dexamethasone suppression test.

Reference Intervals

Morning sample reference interval (6 to 10 a.m.) : 170 – 500 nmol/L

There is a diurnal variation in plasma cortisol; the level is highest shortly before waking and lowest at bedtime.
The following comments apply to early morning samples if the patient is not undergoing an adrenal suppression or stimulation test:
1. An early morning serum cortisol < 170 nmol/L in the absence of recent exogenous steroids is suggestive of primary or secondary adrenal insufficiency. A synacthen stimulation test may be indicated.
2. Early morning cortisol between 170 and 300 nmol/L in the absence of recent exogenous steroids: adrenal insufficiency (primary or secondary) is unlikely but possible. If clinical concern exists, discuss with an endocrinologist .
3. A plasma cortisol higher than 300 nmol/L in an unstressed person excludes adrenal insufficiency (primary or secondary) in the vast majority of cases.
Notes: a new cortisol assay has been used from 2 Sept 2015. The results are approximately 26% lower than the old assay. New reference intervals apply.

Test Method

Performed in: LabPlus Automation
Principle : Competitive type immunoassay with chemiluminescence detection
Reagents: Roche assay
Analyser: Roche Cobas

Limitations / Interference

This assay may cross-react with some exogenous steroids, though in general the degree of cross-reactivity is low compared to the amount of cortisol suppression from the steroid. For dexamethasone, there is minimal cross-reactivity.

Uncertainty of Measurement

Last updated: 04/08/2026

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Testing Laboratory

Department

Delphic Registration Code (Alpha Code)

Test Code (Numeric Code)

Laboratory Handling

Phlebotomy

Transport

Registration

Test Adds Requirement

Sample Stability

Associated Tests

Synonyms

Turnaround Time

Specimen Type

Specimen Requirements

Tube/Container Type:

Preferred

Acceptable

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

No of Samples Required

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

Acceptable

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Pre-testing Requirements

Additional Specimen Information

Diagnostic Use

Interpretation

Reference Intervals

Test Method

Limitations / Interference

Uncertainty of Measurement

Resources

Contact Information

Enquiry Form

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Cortisol (Blood)

Overview

Testing Laboratory

Department

Delphic Registration Code (Alpha Code)

Test Code (Numeric Code)

Laboratory Handling

Phlebotomy

Transport

Registration

Test Adds Requirement

Sample Stability

Associated Tests

Synonyms

Turnaround Time

Specimen

Specimen Type

Specimen Requirements

Tube/Container Type:

Preferred

Acceptable

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

No of Samples Required

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

Acceptable

Preferred Sample Volume (ml)

Minimum Sample Volume (ml)

Pre-testing Requirements

Additional Specimen Information

Referral

Clinical Information/Test Method

Diagnostic Use

Interpretation

Reference Intervals

Test Method

Limitations / Interference

Uncertainty of Measurement

Additional Information

Resources

Contact Information

Contact Information

Enquiry Form

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