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| CANTERBURY HEALTH LABORATORIES |
You have been diagnosed with Cushing's syndrome which results from excessive production of the hormone cortisol, made by the adrenal glands. In your case, the adrenal glands are being driven by excessive amounts of another hormone called ACTH. This test is to determine where that ACTH is coming from. Constant high levels of ACTH are usually caused by a tumour. Approximately 80% of cases are tumours of the pituitary gland while the remainder may occur in the lung, pancreas and other sites (known as "ectopic" sites).
This test relies on the fact that if the source of your high ACTH is the pituitary gland, blood levels taken from very near the gland will be higher than the blood level in an arm vein. Pituitary gland tumours are often tiny and can't be seen even with the most modern scanners. This test will help your endocrinologist to know with almost 100% certainty whether the pituitary gland is the source or if a search is needed elsewhere (for example in the lungs or abdomen). This guides treatment, for example the recommendation for pituitary surgery.
You are allowed water only from midnight the night before (nothing else to eat or drink). You will be given a light sedative, but will be awake during the procedure. You will be taken to the Radiology Department where the procedure will take place. The radiologist will place some local anaesthetic into the groin on each side over the main vein that drains blood from each leg. Then a fine bore catheter will be passed up the vein, past the heart and into the major vein in the neck (the jugular vein). From there it is passed into a smaller vein that drains blood directly from the pituitary gland, known as the inferior petrosal sinus. The procedure is repeated for the other side. X-ray screening guides the radiologist to know where the catheters are positioned. A small butterfly needle is inserted into an arm vein.
Once the catheters are in place, blood samples will be taken from the right and left petrosal sinus, and an arm vein at exactly the same time. After two baseline samples, a hormone called CRH is injected into the arm vein. This increases ACTH when a pituitary gland tumour is present, but has no effect on ectopic ACTH production. Further blood samples are taken for another 10 to 15 minutes, then the catheters are withdrawn. Pressure is applied to the groins to minimise bruising. Often sampling is continued from the arm vein only, for a total of 90 minutes. You will have to remain lying on your back for at least 2 hours afterwards.
This procedure is very safe when performed by an experienced radiologist. Rarely, there have been reports of people having a stroke at the time of this procedure (in the USA, not locally) but this was related to a catheter of faulty design which is now no longer used. Bruising, which is common in Cushing's syndrome, may occur after the catheters are pulled out. Some people notice flushing of the face after the CRH and rarely it can result in a fall in blood pressure.
