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The overnight dexamethasone (DXM) test can give false-positive results in a few conditions (e.g. stress, strenuous exercise, depression, anorexia, anxiety, anticonvulsive therapy) in diagnosing simple obesity and hypercortisolism (HC). The loperamide (LP; a peripheral opioid agonist) test has proven useful in such conditions in adults. Thirty-one obese subjects (age 10.0-19.7 y) were studied by both overnight DXM test and LP test (8 mg orally, samples for cortisol at 0, 90, 150, 180 and 210 min) on 2 separate days. LP suppressed cortisol (< or = 138 nmol l-1) at a dose of 0.1 mg kg-1 bw (half the minimum recommended dose for the drug's antidiarrhoea effect) in 14 subjects who had normal urinary (< 4970 nmol l-1) and serum (< 552 nmol l-1) cortisol, in the absence of signs and symptoms of HC (group A). The DXM test failed to suppress cortisol in three subjects in group A, two of whom were on anticonvulsive treatment. The LP test suppressed cortisol in all of 13 subjects with elevated urinary and/or serum cortisol and/or with signs or symptoms of HC (but in whom HC was subsequently excluded on clinical grounds) (group B), while the DXM test failed to suppress cortisol in three subjects of this group. One of these was under anticonvulsive treatment and one suffered from anxiety and depression. In four patients with Cushing's syndrome (group C) neither DXM nor LP could suppress cortisol levels. Therefore, the sensitivity was 100% for both DXM and LP, while the specificity was 84% for DXM and 100% for LP. No side-effects were observed with either drug. In conclusion, LP is a useful alternative to DXM in those particular conditions that can affect its specificity in children.

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