Cortisol

1. Allow serum samples to clot completely before centrifugation.
2. Within two hours after centrifugation, transfer at least 500 µL of cell-free sample to a storage tube. Tightly stopper the tube immediately.
3. Store samples tightly stoppered at room temperature (15 to 30°C) for no longer than 8 hours. If the assay will not be completed within 8 hours, refrigerate the samples at 2 to 8°C.
4. If the assay will not be completed within 48 hours, or for shipment of samples, freeze at -20°C or colder. Thaw samples only once.

A cortisol test may be used to help diagnose Cushing syndrome, a condition associated with excess cortisol, or to help diagnose adrenal insufficiency or Addison disease, conditions associated with deficient cortisol. Cortisol is a hormone that plays a role in the metabolism of proteins, lipids, and carbohydrates, among other functions. Normally, the level of cortisol in the blood rises and falls in a "diurnal variation" pattern, peaking early in the morning, then declining throughout the day and reaching its lowest level about midnight.