DI Central

How is DI diagnosed?
Before getting to a diagnosis of DI, your vet will need to rule out other diseases that could make your pet pee a lot and drink a lot. Your vet may refer to this as PU/PD for polyuria (pee a lot) and polydipsia (drink a lot.) The most common diseases causing PU/PD include kidney infection or kidney disease, hyperthyroidism (cats), and diabetes mellitus. Other diseases the vet may want to rule out include hyperadrenocorticism (usually dogs, rarely cats), liver disease, hypercalcemia (high blood levels of calcium), acromegaly (cats) and pyometra (infection of the uterus in unspayed female pets only.) Generally, a physical exam coupled with blood and urine tests can help rule these problems out.

The next step is to test the urine and see how concentrated it is. If it has a low specific gravity, your vet may suspect DI.

There is a test that is used to diagnose DI and differentiate between CDI and NDI. This is the water deprivation test (or modified water deprivation test.) Many vets suggest doing this test when they suspect DI. However, you should know that there are dangers and problems associated with this test. There is a safer way to determine if your pet has CDI.

What are the problems with the water deprivation test?

First, since water is withheld, if you pet has DI, they will begin to dehydrate. As part of the test, your vet will weigh your pet. The test does not stop until your pet loses 5% of its body weight (or gets sick from retention of toxins in the blood.) This can be very dangerous. If your vet does this test, be sure to check what type of scales they use to weigh the pet. Baby scales and holding the pet while standing on a human bath scale are probably not accurate enough to make the test safe. If a cat weighs only 6 pounds, 5% of the body weight will be less than 5 oz! So the scales used must be both consistent and accurate enough to show this loss.

Second, since the end point of the test depends on when your pet has lost 5% of its body weight (or gets sick from retention of toxins in the blood), the test may last longer than the vet's office is open. If your vet does this test, be sure that they will stay with your pet until the test ends, even if it is after hours.

Third, to be done right, your pet has to be water restricted for 3 days prior to the actual beginning of the test. If you are not asked to do this, the results of the test may be inaccurate and you may get an incorrect diagnosis. But, if you do water restrict your pet, you must be very careful that they do not get too dehydrated. Doing the water deprivation test on a dehydrated pet is contraindicated! So, you may find yourself in a catch-22 situation!

Puff did go through this test. Believe me, the water restriction was one of the hardest things we have ever done! She was desperate for water! It was very heartbreaking to see how miserable we were making her!

Diabetes Insipidus Topics

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 Information on these pages is the result of personal experience and study.
It was not written by a veterinarian and is not intended to be used as if it was.