Collect a FULL EDTA tube and send to the laboratory without delay.
An EDTA sample can be transported at room temperature but must be separated within 6 hours of collection . If arrival at LabPlus cannot be guaranteed within this time, the sample should be centrifuged and the EDTA plasma separated and frozen before transport.
Thawed and refrozen samples will not be assayed.
Heparin or plain tubes are unsuitable.
Units: pmol/L
|
normal : 2 - 11 (at 0900 hrs) |
Conversion factor : 1 pmol/L = 4.5 pg/mL
Uncertainty of Measurement
: 15%
Performed Weekly.
Principle: Sandwich chemiluminescent immunoassay
Assay: Diasorin
Analyser: Diasorin Liaison
Primary adrenal insufficiency : A plasma ACTH level performed at any time has very high diagnostic accuracy. A high value, usually > 100 pmol/L, is diagnostic of primary adrenal failure while a normal value excludes the diagnosis.
Secondary adrenal insufficiency
: A random plasma ACTH is an unhelpful test in this situation. The value may be normal or low. For the investigation of secondary adrenal insufficiency, the following tests should be considered:
- Serum cortisol at 0900 hours
- Synacthen stimulation test
- Insulin tolerance test
- Overnight metyrapone test
Metyrapone test:
Metyrapone is given, which blocks the 11-hydroxylase step of steroid synthesis. If the HPA axis is intact, this results in a rise in
11-deoxycortisol
to at least 200 nmol/L .
(ACTH also rises, usually to at least 22 pmol/L, but this is not routinely measured as part of the test at Auckland Hospital).
Note that the cortisol result after taking metyrapone is not valid due to crossreaction of cortisol metabolites in the cortisol assay.
Cushing's syndrome : Hypercortisolism should first be confirmed by a high 24h urine cortisol or abnormal low dose dexamethasone suppression test.
If hypercortisolism is confirmed, then a high or "normal" ACTH value (> 4 pmol/L) indicates a pituitary or ectopic source of excess ACTH production, while a low ACTH value (< 2 pmol/L) suggests a cortisol-secreting adrenal tumour or hyperplasia.
References:
1. Chakera AJ, McDonald TJ, Knight BA, et al. current laboratory requirements for adrenocorticotropic hormone and aldosterone/renin sampling are unnecessarily restrictive. Clinical Medicine 2017; vol 17, No 1: 18-21
2. Reisch N, Reincke M, Bidlingmaier M. Preanalytical stability of adrenocorticotropic hormone depends on time to centrifugation rather than temperature. Clin Chem. 2007; 53(2): 358-9. DOI: 10.1373/clinchem.2006.080622
3.Papanicolau et al. Diagnosis and complications of Cushing's syndrome: a consensus statement. J Clin Endocrinol Metab 88: 5593-602, 2003.
4.. Staub JJ, Noelpp B, Girard J et al. The short metyrapone test: comparison of the plasma ACTH response to metyrapone and insulin-induced hypoglycaemia. Clin Endocrinol (Oxf). 1979;10:595-601
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
| Sample | 1 FULL EDTA tube |
|
Sample Preparation
|
- Samples may be transported to the collecting laboratory at room temperature - Separate EDTA plasma within 6 hours of collection - Freeze |
|
Transport to LabPlus
|
- Samples should be frozen prior to transporting to Lab Plus |