of the Week: March
is a cosyntropin stimulation test and how do I do it?
a diagnostic test
to determine the functional reserve of the adrenal gland for the production
of cortisol (also called hydrocortisone, the predominant glucocorticoid
produced by the body).
In patients with normal adrenocortical
function, neurogenic stimuli will cause the release of corticotropin-releasing
factor (CRF) from the hypothalamus. CRF is transported to the anterior
pituitary where corticotropin is secreted . Corticotropin then stimulates
the adrenal cortex to secrete cortisol and several other steroidal substances.
of glucocorticoids include the regulation of protein, carbohydrate, lipid
and nucleic acid metabolism; maintaining the vascular responsiveness to
circulating vasoconstrictors and opposing the increase in capillary permeability
during acute inflammation; and inhibition of the production and action
of the mediators of inflammation.
Cortisol levels respond
within minutes to stress. Elevated levels will protect the organism
under stress; deficiency under stress may lead to hypotension, shock and
death. Patients may be deficient due to prior steroid use, immunosuppresion,
or infarction of the adrenal glands.
Cosyntropin is a
synthetic polypetide which is identical to the portion of corticotropin
that has full biological activity. It is the preferred agent
for stimulation tests as it is far less immunogenic than exogenously produced
corticotropin and less likely to produce allergic reactions.
obtain a baseline
cortisol level (7 ml red top tube);
administer 250 ug
(0.25 mg) cosyntropin in 50 ml NS IV over 5 minutes (may also be given
obtain second cortisol
level 30 minutes post infusion of cosyntropin.
criterion for a normal
response is a stimulated cortisol level of >500 nmol/L (>18 ug/dL) and
a minimal stimulated increment of >200 nmol/L (>7 ug.dL) above baseline;
test performed only
on Wednesdays thus may be delay in obtaining results;
baseline serum levels
will be higher in the morning than in the evening due to diurnal variations,
but the test may be done at any time of the day;
baseline levels may
be higher in patients receiving hydrocortisone, oral contraceptives or
pregnant patients, severely ill patients;
LHSC lab uses the
luminescent assay, which may erroneously measure spironolactone, hydrocortisone
and cortisone; these agents should be held on the day of the test.
Prednisone, dexamethasone, betamethasone and methylprednisilone will not
be measured and may be given on the day of the test.
to Suppression test:
are used to document hypersecretion of the adrenal glands (such as in Cushing's
when blood levels
of glucocorticoid are increased in normal individuals, less corticotropin
is released from the pituitary and less steroid is produced by the adrenal
gland. The integrity of this feedback mechanism can be tested clinically
by giving a glucocorticoid and judging the suppression of cortisol secretion
the best screening
test is administration of dexamethasone 1 mg po at midnight with measurement
of plasma cortisol at 8 am the next morning. This value should be
<140 nmol/L (<5 ug/dL) in normal individuals.
Hospital Formulary Service Drug Information, 2000.
Principles of Internal Medicine, 14th Edition.