Overnight dexamethasone suppression test: a reliable screen for Cushing's syndrome in the obese.
OBJECTIVE
Reevaluation of the validity of the 1-mg overnight dexamethasone suppression test (ODST) as a screening test for Cushing's syndrome in obese patients.


METHODS
Eighty-six obese patients (body mass index, 30 to 53 kg/m(2)) that were referred to a general endocrine outpatient clinic for evaluation of simple obesity, diabetes mellitus, hypertension, polycystic ovary disease, or pituitary tumor. One milligram dexamethasone was administered orally at 11:00 PM, and serum cortisol levels were measured the following morning between 8:00 AM and 9:00 AM. Suppression of serum cortisol to <80 nM (3 micro g/dL) was chosen as the cut-off point for normal suppression. Patients with serum cortisol levels > or =80 nM were evaluated for Cushing's syndrome.


RESULTS
Suppression of morning cortisol levels to <80 nM occurred in 79 of the 86 obese patients. Seven patients had serum cortisol levels higher than 80 nM; five were eventually diagnosed with Cushing's syndrome and two were considered false positive results in view of normal 24-hour free urinary cortisol and normal suppression on a low dose dexamethasone suppression test (0.5 mg of dexamethasone every 6 hours for 2 days). We found a false positive rate of 2.3% for the ODST using a cut-off serum cortisol of 80 nM.


CONCLUSIONS
The ODST is a valid screening test for Cushing's syndrome in the obese population. The false positive rate was 2.3%, even when using a strict cut-off serum cortisol of 80 nM. Abnormal cortisol suppression in obese patients should be investigated and not be considered false positive results.
Ness-Abramof
Rosane
R
Section of Endocrinology, Diabetes, and Nutrition, Boston Medical Center and Boston University School of Medicine, Massachusetts 02118, USA. rosane.abramofness@bmc.org
Nabriski
Dan
D
Apovian
Caroline M
CM
Niven
Mark
M
Weiss
Eliahu
E
Shapiro
Menachem S
MS
Shenkman
Louis
L
D000328:Adult; D015992:Body Mass Index; D003480:Cushing Syndrome / Q000150:complications / Q000175:diagnosis*; D003907:Dexamethasone; D005189:False Positive Reactions; D005260:Female; D005938:Glucocorticoids; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*
D005938:Glucocorticoids; D003907:Dexamethasone; D006854:Hydrocortisone