Automating the Analysis of Urinary Free Cortisol
The measurement of urinary free cortisol is used in the investigation of possible Cushing’s syndrome. Cortisol is a steroid-hormone synthesized from cholesterol by a multienzyme cascade in the adrenal glands. It is the main glucocorticoid in humans and acts as a gene-transcription factor influencing a multitude of cellular responses in virtually all tissues. Only a small percentage of circulating cortisol is biologically active (free), with the majority of cortisol inactive (protein bound). As plasma cortisol values increase, free cortisol (i.e., unconjugated cortisol and hydrocortisone) increases and is filtered through the glomerulus. Urinary free cortisol (UFC) in the urine correlates well with the concentration of plasma free cortisol. UFC represents excretion of the circulating, biologically active, free cortisol.
At our laboratory in Cambridge we have been working on a minaturised automated solid phase extraction (SPE) method for the extraction and clean-up of urinary free cortisol, followed by tandem mass spectrometry detection. We have been conducting work with spiked urine and commercially available QC materials. To follow soon will be an application note detailing the performance characteristics of the method and recovery data. Currently the automated extraction takes four and a half minutes, which fits well within the LC cycle time of seven minutes, this allows for highest possible throughput for this clinically important assay.