Endocrine Abstracts

Urine free cortisol (UFC) is analysed in 24 h urine collections in suspected Cushing’s syndrome, and provides an integrated measure of cortisol secretion over the whole day. The aim of this audit was to review how clinically useful UFC results were, and whether this analytical service was still justified. The current automated immunoassay with manual sample preparation was time-consuming, expensive (disproportionate quality control / external quality assessment (EQA) sample analysis, and unused reagent frequently discarded), and prone to cross-reactant interference.

Requests from April 2010 to March 2011 were examined. Of 202 samples, 102 were requests from within the Trust, mainly from Adult Endocrinology (40%), 22% were EQA samples, and 28% were GP or referred samples.

Of internal requests, 34% were clinically appropriate (e.g. ‘Cushing’s syndrome’, ‘hypertension’, ‘relapse, known Cushing’s’), and 17% were inappropriate (e.g. ‘adrenal insufficiency’, ‘tall stature’ (paediatric), ‘renal stones’). Analysis was hampered, as 48% of requests had no clinical details. For 20% of requests a random urine sample was sent, the results of which are not clinically interpretable.

Clinical details, sample type, and whether the UFC result was raised or normal (<340 nmol/24 h) were considered in conjunction with the results of other biochemical and dynamic function tests to judge whether the test had ‘added value’ in the patient pathway. In only 10% of requests was the UFC test considered to add value. In a further 12% of samples UFC may have added value, although dynamic function testing was preferable (e.g. 48 h low dose dexamethasone suppression test).

Discussion with the clinical colleagues informed a consensus regarding when UFC is clinically required, and it was agreed to switch the assay to an LCMS method, which is more specific. Measures introduced following the audit have reduced requests by 30%, and prevented inappropriate samples and requests being assayed, reducing analyses by 80%.