Pathology tests database

Sample and container requirements

Serum Lithium Heparin Plasma (paediatrics only)

Minimum volume required

Special requirements

None

Patient preparation

The collection time should be noted on the request form.

Sample viability

Turnaround time

This assay is run throughout the day and night. The in-lab turnaround time is normally less than 24 hours.

Reference range

Before 10 am: 101 – 536 nmol/L After 5 pm: 79 – 478 nmol/L (Source: Abbott Diagnostics) In the investigation of suspected adrenal insufficiency, morning (08:00 – 09:00) cortisol measurements are most informative. Guidance from NICE (NG243) suggests that a cortisol <150 nmol/L is consistent with adrenal insufficiency, while >300 nmol/L makes it very unlikely. Values between 150 – 300 nmol/L are indeterminate and may require further assessment with a short synacthen test (SST), depending on the clinical context.

Clinical guidance

Cortisol is the most significant glucocorticosteroid and is essential for the maintenance of several body functions. Please refer to LabTestsOnlineUK to learn more about cortisol. https://labtestsonline.org.uk/tests/cortisol-test

Notes

Please include the clinical indication for the cortisol request and state whether the patient is currently taking any exogenous steroids on the request form. Pregnancy, contraceptives and oestrogen therapy give rise to elevated cortisol concentrations. Samples from patients treated with prednisolone, methyl-prednisolone or prednisone may give falsely elevated concentrations of cortisol. Therefore, if your patient is taking these mediciations please order a Prednisone Test.