Specimen Collection
LOW DOSE OVERNIGHT DEXAMETHASONE SUPPRESSION TEST
SPECIMEN:
|
Day 1:
0900h:
5 mL blood. PST tube preferred. Request "
cortisol
".
2300h:
Give 1 mg dexamethasone, orally.
|
|
Day 2:
0900h:
5 mL blood. PST tube preferred. Request
"post-dexamethasone cortisol
".
|
Reference Intervals
Plasma cortisol (nmol/L): Reference ranges
|
Day 1
basal
|
0900h:
|
170 - 500
|
|
Day 2
post DMZ
|
0900h:
|
<50: excludes Cushings syndrome
50 - 100: Equivocal result - may be normal but is also consistent with early Cushings disease
>100: Cushings syndrome
|
-
High dose Suppression Test: - see below, under Diagnostic Use.
Diagnostic Use and Interpretation
Failure to suppress plasma cortisol to <100 nmol/L indicates the presence of
hypercortisolism
.
Suppression to <50 excludes Cushings syndrome. Suppression to levels between 50 and 100 may be normal, or may be consistent with early Cushing's.
False positives may be due to failure to take the DEX , vomiting, or malabsorption.
Hypercortisolism can be due to:
-
Cushings syndrome (due to pituitary, adrenal, or ectopic ACTH tumours)
-
Sickness or stress can cause increased cortisol production and lack of suppression.
-
Pseudo-Cushing's syndrome from alcohol abuse, or depression
Differential diagnosis of the cause of Cushing's syndrome:
A combination of clinical assessment, plasma ACTH measurement, high dose dexamethasone suppression test and possible venous catheterisation of petrosal veins is required to establish the source of the hypercortisolism.
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