Inferior petrosal sinus sampling

Investigation Protocol

Indications

To help distinguish between ACTH dependent Cushing’s syndrome of ectopic and pituitary causes.

Patient preparation and precautions

Patients should be fasting from midnight (water only). Patients should bring all their usual medication with them to take after the test, and for documentation. Full blood count, clotting screen and renal function must be documented as normal prior to the test. Blood should also be taken for 'group and save' prior to the test in case transfusion is required.

Allergic reactions, flushing and hypotension have been described after ovine CRH and so the test must only be performed with full medical support present, although human CRH is now in wide usage.

Procedure

Insert a cannula gauge 20 with a three-way tap, and using a syringe or the vacutainer connector system, fill one plain clotted bottle for cortisol, and one EDTA tube for ACTH. This forms the t= -15 minute sample. Both tubes need to be labelled, then the EDTA tube centrifuged, separated and frozen before transport to the laboratory.

Repeat this basal sampling after 15 minutes, and label t= 0 minutes.

The radiologist will then perform selective venous sampling of the petrosal sinuses, via a femoral puncture. After successful bilateral cannulation of the petrosal sinuses, samples will be taken from both petrosal sinuses, and from a peripheral vein, and labelled time 0 prior to CRH. 100mcg CRH is then administered as a bolus via a peripheral cannula. Sampling is then repeated from both sinuses and a peripheral vein, at 2, 5 and 10 minutes after CRH infusion. All samples are taken into EDTA tubes, for immediate centriguation, to be assayed for ACTH only.

The detailed protocol for inferior petrosal sinus sampling is beyond the scope of this guide.

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Patient information sheet

Inferior petrosal sinus sampling

Your doctor has arranged for you to undergo a test called inferior petrosal sinus sampling. The purpose of this is to help us to find out if your pituitary gland is producing the right amount and type of hormones. This involves taking a series of blood samples from the veins draining the inside of the head.

It is normal for patients to be admitted to hospital early on the day of the procedure and to go home later in the day if they are well, sometimes this is not until the evening. There is no special preparation before the procedure apart from a blood test which you must have done about two to three days before the appointment date. 

Please come to the ward at 8am on the morning of the test. We need you in early to prepare you (get you into a special theatre gown and for a doctor to come and talk to you and examine you). You can eat and drink but it is preferable to have a light breakfast because you will be lying flat on an x-ray table during the procedure and in a bed for a few hours after. 

If you are taking Metyrapone then please stop this for five days prior to the procedure. 

The procedure is undertaken in the angiography suite (a special x-ray room) by one of our consultant radiologists (x-ray doctor). They will explain what will happen and you will be able to ask questions before you are asked to sign a consent form. This is your agreement to have this procedure.

During the procedure you will be asked to lie flat on a special X-ray table. The skin in both of your groins will be cleaned with cold fluid before you are given an injection of local anaesthetic to numb the area. You should not feel any pain following this, but you will feel some gentle pushing as catheters (special tubes) are inserted into the main vein in each groin. The catheters are then guided through the veins up into the vein near your pituitary gland.

X-rays are taken during this time to make sure that the catheters are being guided to the correct place. Some patients have reported feeling a sensation behind their nose and eyes during this process, but this is not unpleasant. Once the catheters are in their final position, this is checked by injecting some x-ray contrast. While this is happening patients have reported experiencing a rushing noise in their ears, which lasts for no more than a second or two.

A series of blood samples are then taken over a period of 10 minutes. During this time you will also be given an injection of a hormone, called CRH, through one of the catheters. This may cause you to feel a 'flushing' sensation for a few seconds.  

Once the necessary blood samples have been obtained the catheters are then removed. The nurse will apply gentle pressure to the groin area for about 5 minutes to help stop any bleeding from the small puncture wounds. You will be asked to remain lying flat for about half an hour before you are returned to the ward and gradually allowed to sit up in bed. Following a period of time you will be able to mobilize, get dressed and if all is satisfactory you will be allowed to go home.

If you have any queries about this procedure, please contact: 

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