Hydrocortisone day curve

Investigation Protocol


Monitoring the adequacy of hydrocortisone (+/-fludrocortisone) replacement therapy in patients on replacement therapy. This includes patients with hypopituitarism, Addison’s disease, adrenal failure of other causes or post adrenalectomy.

This is also performed to monitor patients with Nelson’s syndrome.

Preparation and precautions

Patient may eat and drink normally prior to the test, but must bring in all their usual medication to be documented and to take after the first blood test at 8am. Estrogen containing medications, including the contraceptive pill and hormone replacement therapy, should be stopped for six weeks prior to measuring serum cortisol. This is because estrogen induces cortisol binding globulin and leads to elevations in measured serum cortisol. Any other steroid containing medications should also be avoided, as they may interfere with the hypothalamo-pituitary-adrenal axis, or cross react with the cortisol assay.


Cannulation may be offered. Insert cannula gauge 20 with a three-way tap, and using the vacutainer connector system or a syringe fill one plain clotted tube for each sample taken. Clearly mark with the patient’s details, date and time of sample.

Samples for serum cortisol are taken at t=0 (typically 8am) prior to the patient’s first hydrocortisone dose, then at one, two, five and nine hours after this dose. For patients taking hydrocortisone three times a day, the second dose should be given after the five hour sample and the third after the nine hour sample. Patients taking hydrocortisone twice daily should take their second dose at seven hours with an additional sample taken at that time. Clearly mark the patient’s details, date and time on each bottle.

The nurse or doctor looking after the patient will ask and document  the exact time and dose of steroids taken by the patient. This should be recorded on the request form, in the patient’s notes and results sheet. 

In some cases, or for research purposes, additional samples may be taken at 30 minutes, and then hourly for 11 hours after the first dose is taken.

Post adrenalectomy, and in patients with Addison’s disease, ACTH and renin may also be requested. In this case, additional blood should be drawn into an EDTA tube for ACTH, and into a lithium heparin tube for renin, at times 0 and 120 minutes pre and post the first hydrocortisone and fludrocortisone doses. These samples need to be labelled, then centrifuged, separated and frozen before transport to the laboratory.

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Patient information sheet

Hydrocortisone day curve

Your doctor has referred you to have a series of blood tests performed over a day. This is to see if you are taking the correct amount of steroids as a replacement for your body’s daily requirements.

We will be taking a sample of blood at 8am, 9am, 10am, 1pm and 5pm. You will be resting in a reclining chair in the unit throughout the test. You may eat and drink as normal on the day of the test. If you are in the unit over the lunch period you will be offered something to eat. You do not have to stay in the unit for the whole day but you may do so if you choose.

Please bring all your medications with you to be checked and documented on the day. We need to take the first blood test just before your first dose of hydrocortisone, so it is usually easier if you bring tham all with you to take on the unit. However, if you take the contraceptive pill, hormone replacement therapy, or any other steroid tablets, nasal drops, inhalers, skin cream, or have recently had a joint injection, it is important that you inform us before the test date.

You may take your other medication as normal on the day of the test. However, if you take any steroid tablets, nasal drops, skin creams, or have recently had a joint injection, it is important that you inform us before the test date. You can contact us either by writing to the address at the top, or by phoning the number given at the end of this sheet.

You may wish to bring a book or magazine to read. We do have a radio, or you can access Patientline; alternatively you may like to bring your own personal radio/cd player (please bring your own headphones). You may bring someone to stay with you during the test but there is not enough space for more than one person.

Children are discouraged, as this can be disruptive to other patients. However, if this poses a particular problem for you please discuss this with the senior nurse in the unit. You should be able to undertake normal activities after the test is finished and it should not interfere with your ability to drive home. 

If you have any queries about the test, please contact:

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