Analysis of sweat is well-established for the diagnosis of cystic fibrosis and for testing for drug abuse. Cortisol, cortisone and aldosterone were identified in sweat in 1948, and the presence of 11 beta hydoxysteroid dehydrogenase type 2 in the epidermis was reported in 1990. At present there are no studies of the diagnostic value of sweat cortisol measurement. We have evaluated the use of a sweat patch comprising a small 47 by 32 mm rectangle of filter paper secured by a waterproof dressing which allows the skin to breathe. Patches were worn on the upper arm for 7 days by 24 healthy volunteers and by 5 patients with Cushing's syndrome ( 4 with pituitary adenoma, 1 with adrenal adenoma). Samples were also collected for salivary cortisol profiles and 24 hour urine cortisol.
Sweat patches were extracted into distillled water and an aliquot taken for sodium assay. They were then extracted into dichloromethane and the dried extract was analysed with a DELFIA salivary cortisol assay which can detect 1.3 nmol per litre cortisol.
Sweat cortisol / sodium ratios in Cushing's patients were all above the upper limit of 200 nanomoles per mole sodium established in normal subjects.
For combined patient and cortisol results correlations were found between sweat cortisol/ sodium ratios and 24 hour urine cortisol ( r equals 0.93; p less than 0.0001), the area under the salivary cortisol day curve ( r equals 0.53; p equals 0.027) , and morning salivary cortisol ( r equals 0.56; p less than 0.01)
Sweat patch cortisol/ sodium ratios can be used as a non-invasive screen for Cushing's syndrome alongside salivary cortisol measurements, and have advantages for the investigation of cyclical Cushing's syndrome.
22 - 24 Mar 2004
British Endocrine Societies