Specimen Collection

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

Sample stability:

• 24 hours at 20-25 ^o C
• 4 days at 2-8 ^o C
• 12 months at -20 ^o C

4.5 mL PST Blood (Preferred)

0.5 mL Paediatric Micro-PST Blood (Preferred)

4 mL EDTA Blood

5 mL Heparin Blood

4 mL Plain Blood

3.5 mL SST Blood

0.5 mL Paediatric Microsample Blood
Reference Intervals

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

Uncertainty of Measurement: 6%

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.

Turnaround Time: Within 3 hours
Assay Method

Principle : Competitive type immunoassay with chemiluminescence detection

Reagents: Roche Elecsys Cortisol II

Analyser: Cobas e801

Diagnostic Use and Interpretation

Random or early morning cortisol measurements are of limited value due to the diurnal variation. Appropriate stimulation or suppression tests are usually necessary to determine the status of the HPA axis.

Hypercortisolism (Cushing's syndrome) may be due to pituitary or adrenal tumours, or to ectopic ACTH-secreting tumours.

In Cushing's syndrome, the early morning cortisol is often within the reference interval.

Screening tests for Cushings syndrome:

24 hour urine cortisol

Bedtime urine cortisol/creatinine ratio

Bedtime plasma cortisol

Bedtime salivary cortisol

Overnight low-dose dexamethasone suppression test

Plasma cortisol concentrations are decreased in Addison's disease and hypopituitarism and in patients taking synthetic glucocorticoids (e.g. prednisone, dexamethasone).An ACTH level can help to distinguish these conditions. Past prolonged exogenous steroid use can suppress endogenous ACTH and steroid production for weeks to months, even after stopping the exogenous steroid. A careful examination of the patient's medications, including oral, topical, inhaled, intra-articular and other injected steroids is important in this situation. Steroids injected into joints etc. may have a very long half-life (days to weeks). Some remedies/supplements bought overseas may have added steroids and may be associated with abnormal cortisol results. If the clinical features do not match the laboratory results, please contact the on-call chemical pathologist.

Variable cross-reactivity with other steroids can occur as demonstrated in the downloadable document below (see " Roche Elecsys Cortisol II assay steroid cross-reactivity").

Dexamethasone Test

Synacthen test

Download: Roche Elecsys - Cortisol II assay steroid cross-reactivity.docx

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Last updated at 15:26:00 06/01/2025