Arginine stimulation test (with copeptin measurement)

What is an Arginine Stimulation Test?

Your doctor has requested that you have the Arginine Stimulation Test (AST) with copeptin measurement has been requested by your doctor to investigate whether you may have arginine vasopressin (AVP) deficiency.

This condition, is also known as central diabetes insipidus, can lead to an inability to concentrate urine which in turn can lead to

• large urine volumes
• thirst
• increased fluid intake.

Arginine is an amino acid that stimulates release of a number of pituitary hormones. This should stimulate the hypothalamus and pituitary to release the hormone AVP.

AVP acts on the kidneys to concentrate urine and reduce urine output. Because Copeptin is released at the same time and is more easily measured; it is used as an indicator for the AVP concentration in your blood.

How you need to prepare for the test?

In preparation for the test, please:

• Fast (no food) from midnight before the test.
• Only drink plain water during the fasting period.
• Do not drink fluids (water, tea, coffee, etc.) for at least 2 hours before the test starts. This start time will be indicated in your appointment letter.
• Avoid nicotine and alcohol for 24 hours prior to the test.
• Avoid strenuous exercise for 24 hours prior to the test.
• If you are taking a medication called Desmopressin (DDAVP), you should usually stop taking it 24 hours prior to your visit (or omit your 8pm dose the night before). This can be discussed with your medical team.
• Bring all of your regular medications with you.
• Let us know if there is any possibility that you may be pregnant.

What happens on the day of the test?

Please come to the Endocrine Investigation Unit, Wolfson Diabetes & Endocrine Clinic (Clinic 32), Addenbrooke's Treatment Centre at Addenbrooke's Hospital and check in at reception. The test should last no more than 4 hours. You may wish to bring something to read or occupy yourself with (a quiet activity).

Upon arrival, we will measure your weight and height in the first instance. We will also need to collect a small sample of urine.

Two small plastic cannulae (thin tubes) are placed in a blood vessel of each arm: one is used for the infusion of arginine (over 30 minutes), the other is used for regular blood sampling during the test. Your blood pressure and heart rate will also be checked regularly, and we will ask you before and after the test about any symptoms you may be experiencing.

Before and at 60 and 90 minutes after the start of the infusion, blood samples for later copeptin measurements are taken. The catheter is flushed with a saline solution after each blood sampling. At the end of the test, the plastic catheters are removed and you are allowed to eat something before being discharged.

Will I experience any side effects?

Thirst and mild nausea are the most commonly reported symptoms, and may be experienced by some patients. Although the medical licence for arginine does not include this test, it has been widely used for endocrine testing such as this for many years.

When will I get my results?

The results can take some time to process and interpret. They will be discussed with you at a later date by your medical team.

MyChart

We would encourage you to sign up for MyChart. This is the electronic patient portal at Cambridge University Hospitals that enables patients to securely access parts of their health record held within the hospital’s electronic patient record system (Epic). It is available via your home computer or mobile device

More information is available on our website: MyChart

Contacts/further information

Please contact the Endocrine Investigation Unit and leave a message on 01223 217848 (voicemail) from 09:00 – 16:00, Monday – Friday.

References/sources of evidence

A Copeptin-Based Approach in the Diagnosis of Diabetes Insipidus. Fenske et al. N Engl J Med 2018;379:428-39.