Test Background Cortisol is secreted in a diurnal pattern with peak values occurring in the early morning. Random serum cortisol may be difficult to interpret. The diurnal rhythm may be disrupted or lost in Cushing’s syndrome. Free cortisol measured in a 24 hour urine collection may be a more useful diagnostic tool in some patients.
Clinical Indications Most specific diagnostic indicator of Cushing’s syndrome Differential diagnosis of phaeochromocytoma and Conn’s syndrome
Reference Range 50-270 nmol/L
Sample Required 24 hour urine collection
Sample Collection Please include time and volume for the 24 hour collection.
Sample Volume 1 mL
Stable at 2-8oC for 24 hours. Please freeze pending dispatch for analysis.
Can be sent by first class post.
Turnaround Time 2 weeks
Notes Acidified samples are unsuitable for this assay.