A rare cause of Cushing's syndrome demonstrates analytical discrepancies between the Roche E170 and Bayer Centaur testosterone assays.

The initial biochemical investigations of a female patient with suspected Cushing's syndrome revealed abnormal endocrine results, including a marked elevation of serum testosterone. Overnight and low-dose dexamethasone suppression tests confirmed the diagnosis of Cushing's syndrome. Imaging investigations revealed an appearance compatible with adrenocortical carcinoma with metastases in the lungs and liver. This tumour is a rare cause of Cushing's syndrome. Two different automated testosterone immunoassays were used during the investigation of this patient, and analytical discrepancies in the patient's testosterone results were found. The two assays used, as well as potential causes of the difference in results will be discussed.