There are a number of tests for AVP Deficiency which can lead to a diagnosis. AVP Deficiency is also known as diabetes insipidus and people with this condition often have excessive urine production.
What tests are carried out and how will these feel?
Investigation methods for patients with excessive urine production would be:
- Measurement of 24 hour urine output
- Measurement of plasma osmolality from a blood test (a measure of sodium and glucose circulating in the blood)
- Water deprivation test (described below)
The water deprivation test deprives you of fluid for 6-8 hours to see if there is a reduction in the volume of urine. You can expect to feel quite thirsty during this test. The next stage is to give you a small quantity of desmopressin, usually as an injection. If you have CDI, you should notice a reduction in the amount of urine you pass. This shows that your kidneys are responding to the hormone.
If you have NDI, this response does not occur or is impaired, as the kidneys don’t recognise the effect of the hormone in small doses. Once you are allowed to drink again, you will begin to feel better. If you need other hormone treatments, you will need to continue taking them during the test. This test can be performed as a day case.