A safer way to determine if your pet has CDI
Rather than put your pet through the dangers and the discomfort of a water deprivation test, your vet can do, or, better yet, have you do, an ADH (or DDAVP) trial. This is a VERY SAFE test and can be done at home.This test is mentioned in "The 5 Minute Veterinary Consult, Canine and Feline" by Larry P. Tilley and Francis W. K. Smith, Jr., (Published by Williams and Wilkins, 1997), in the section on Diabetes Insipidus, p. 514. The details are very sketchy, but here is what the book says in the section “DIAGNOSIS / Other diagnostic procedures … ADH trial -- therapeutic trial with synthetic ADH product (DDAVP®); a positive response (water intake decreases by 50% in 3–5 days) is diagnostic for central diabetes insipidus. Note: all other causes of polyuria and polydipsia (PU/PD) should be ruled out before conducting an ADH trial.”
This test is also mentioned specifically for cats in the monograph on Desmopressin Acetate in "Veterinary Drug Handbook" by Donald C. Plumb, Third Edition, Iowa State University Press, 1999. The section of the monograph is as follows: "CATS: To help differentiate central diabetes insipidus from the nephrogenic form: 1 drop into the conjunctival sac twice daily for 2-3 days; a dramatic reduction in water intake or a 50% or greater increase in urine concentration gives strong evidence for a deficit in ADH production. For treatment of central DI: 1-2 drops into the conjunctival sac once or twice a day; duration of activity 8-24 hours. (Bruyette 1991)"
To do this test, your vet will need to get desmopressin acetate (generic name) or DDAVP (brand name) nasal spray. You can either instill two to three drops of the solution into your pet’s eyes twice a day, or you can inject 0.05 mL under the skin twice a day (see the section on treatment by injection for more details on doing the injections.)
We have found that the injections will give you a better test because they are absorbed better and act for longer than the eye drops. Plus, if you use the injections for your test, it appears that the 2-3 days of water restriction prior to the test are unnecessary. If you use eye drops for the test, you may still have to do the water restriction.
You will need to measure water consumption for a 12 hour period before the test begins. Measuring water intake is pretty easy to do. If you have more than one pet, you will need to isolate the pet suspected of having DI when you measure water consumption. Then fill the water bowl to a known level and be sure the pet has access to NO other sources of water (no dripping faucets, no toilets, etc.). After 12 hours measure how much water you need to add to bring the bowl back to the same level as when you started. Record how much water has been consumed in 12 hours.
Now start the medication and after 4-10 doses of it (2-5 days), you will need to again measure water consumption for a 12 hour period. If you see a 50% decrease in consumption, your pet may have Central Diabetes Insipidus.
If you cannot measure water consumption (cannot isolate the pet from others or for any other reason), your vet can get a urine sample before you start the test and determine its specific gravity. Then, within 8 hours of the last dose of medication, have your vet again get a urine sample and check the specific gravity. If the specific gravity has increased significantly, your pet may have Central Diabetes Insipidus.
For this test to work, the pet MUST get enough of the drug.
From the experience of people we have helped over the past couple of years, we believe you need to stop the medication and verify the return of abnormal water consumption or quite low urine specific gravity before deciding for sure that your pet has CDI. You do not want to treat with an expensive drug if you do not need to, no matter how safe the drug appears to be! There have been a couple of animals where excessive water drinking was observed and then went to a normal level on a DDAVP trial. But when the drug was stopped, water consumption continued at the normal level and did not go back to the high levels observed before the 3-5 day trial with the drug.
So, to sum up how to do the DDAVP trial:
• Measure water consumption OR measure urine specific gravity before the test begins
• Give plenty of the drug for 3-5 days
• Measure water consumption OR measure urine specific gravity at the end of the 3-5 days, but WHILE STILL giving the drug
• Stop giving the drug
• Wait a day or two and again measure water consumption OR measure urine specific gravity
If your pet responds while getting DDAVP, then gets worse (drinks more and/or has less concentrated urine) when you discontinue it, then gets better if you start it again, it is pretty certain that he has CDI.If he does not respond (does not drink much less and/or still has a low urine specific gravity), he may have DI, but it is not CDI or he may have some other disease that causes the same symptoms as DI does.
Diabetes Insipidus Topics
It all started with Puff ... DI Central home What is diabetes insipidus How is DI diagnosed What are the problems with the water deprivation test A safer way to determine if your pet has CDI If your pet has been diagnosed with nephrogenic diabetes insipidus Traditional treatments Treatment of central diabetes insipidus by subcutaneous injection of desmopressin References Where your vet can get more information and help How to treat by subcutaneous injection of desmopressin What you need How much to use Breaking into the bottle and transferring the drug Pictures to guide you the first time through What about using the pills? How to keep the cost down A cost comparison - eye/nose drops vs. injections Puff's opinion - Use the injections … here's why A picture gallery of pets with diabetes insipidus Puff's story You can email Puff for more information or to ask questions.
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It was not written by a veterinarian and is not intended to be used as if it was.