Glucocorticoids Laboratory Tests

ACTH Stimulation Assay

Baseline serum cortisol + administer 250 ug Cosyntropin (synthetic ACTH)

ACTH Stimulation Assay

Normal response: > 18-20 ug/dL

Overnight Metyrapone Test

Inhibits 11-ß-hydroxylase

Cosyntropin

Synthetic ACTH

Overnight Metyrapone Test

Normal: 11-deoxycortisol >7 ug/dL (200 nmol/L)

CRH Test

> Safe but expensive

CRH Test

IV: 100 ug ovine or human CRH

high ACTH

-Primary Al: _post-CRH

Urine Free Cortisol

Sensitive indicator of endogenous cortisolism

Urine Free Cortisol

> When serum cortisol exceeds the capacity of its carrier protein binding, free cortisol levels rise rapidly, increasing the free cortisol filtered into the urine

Urine Free Cortisol

> Affected by hydration (3-5 L/day)

24-Hour Urine Cortisol

• measured by Tandem Mass Spectrometry

24-Hour Urine Cortisol

• most sensitive and specific for excess cortisol

Urine 17-Hydroxycorticosteroid

Produced when the liver and other tissues break down cortisol

CRH Stimulation Test

> Helpful in distinguishing forms of ACTH-dependent Cushing's Syndrome

CRH Stimulation Test

Cushing: High ACTH

Ectopic ACTH syndrome: same before and after

Dexamethasone Suppression Test

> As cortisol substitute, suppresses ACTH if the pituitary gland is normal and cortisol secretion if the adrenal gland is normal