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Old May 28th, 2008, 04:18 AM
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Pets drinking too much - Lecture - By Dr. Lee

There have recently been a few posts on increased water consumption in both dogs and cats so I thought I would write a small crash course lecture on it. So if you are ready, or just can’t sleep, here we go!

PU/PD 101


My pet drinks a lot of water. That’s good right?


Not always. In fact, if it is noticeable or the increase in urination is greater in amount then there may very well be a problem. Increased water consumption or increased urination is call PU/PD or PolyUria/PolyDipsia in the medical realm. Remember what goes in must come out – so increased thirst and increased urination are linked. Occasionally some medical source will sublist the causes as those that cause primary increased thirst with secondary increased urination and those that cause primary increased urination with secondary increased thirst. Usually these are all lumped together since most are a primary increase in urination. Why does this occur? Simply, because the kidneys cannot concentrate the urine so the urine isothenuric, that is the same concentration as the blood. So if my pet has PU/PD then, it must have kidney disease? No. While it is from inability to concentrate, many other factors can influence normal kidneys into PU/PD.
So what causes PU/PD. Usually you will hear vets, and myself, talk about the twelve causes of PU/PD. While this is a wonderfully biblical number, it is an oversimplification. A list which appears below, complied by Dr. Kathy James, lists a more complete 15 causes. If we look at the most common causes, then twelve usually works well. Also dogs and cats have some causes which are the most common.

Most common Causes – top five
Dogs: Diabetes Mellitus, Kidney disease, Kidney Infection, Liver Disease, Cushing’s diseas
Cats: Kidney disease, Diabetes mellitus, Hyperthyroidism, Kidney infection, Liver disease

Complete list for dogs and cats compiled by Dr. Kathy James from VIN, the Veterinary Information Network at U.C.Davis.
(some of these have some major nerdy medical terms, I included this for completeness and to show how complex this can be. I reduced the terms to English only briefly or not at all so this would stay only a thread and not turn into a sweater!)

1. Hyperadrenocorticism (Cushing’s disease)
2. Hypoadrenocorticism (Addison’s disease)
3. Hypercalcemia (high blood calcium)
4. Diabetes mellitus (basic diabetes that most people are familiar with – high blood sugar)
5. Hepatic disease (Liver disease)
6. Pyelonephritis (kidney infection)
7. Leptospirosis (bacterial spirochete infection of the kidneys – a tropic and subtropic disease)
8. Chronic Renal Disease/Renal Failure (May be present without any blood laboratory changes)
9. Hyperthyroidism (over active thyroid, similar to Grave’s disease in people (John Adams was thought to have this disease). It is rare, very rare in dogs)
10. Hypokalemia (Low blood potassium)
11. Pyometra (infection of the uterus)
12. Renal Tubular Diseases (in basenji’s it is called Fanconi’s Syndrome)
13. Chronic Partial Urinary Obstruction or Post-Obstructive Diuresis (urethral obstruction, like a urinary stone lodged in the penis – common in cats)
14. Iatrogenic (caused by human intervention, either therapeutic or not) Disease due to medications such as lasix (diuretic commonly used in heart failure management), phenobarbitol (used to control seizures) ot diets too high in salt or heavily restricted in protein.
15. Pheochromocytoma (unusual intra-abdominal tumor of the adrenal gland)
16. Polycythemia (condition where too many red blood cells are made)
17. Acromegaly (usually have concurrent diabetes mellitus)
18. Paraneoplastic syndromes (syndromes created by the affects of cancers)
19. Pericardial Effusion (fluid accumulation in a sac that envelopes the heart)
20. Psychogenic Polydipsia (as in a true behavioral disorder with a compulsive element)
21. Primary Non-Medical Polydipsia (AKA “I drink a lot because I like it or I engage in activities that promote it, but that doesn’t mean I’m sick”)
22. Primary Nephrogenic Diabetes Insipidus
23. Hypertension
24. Atypical Cushing’s and SARDS
25. Central Diabetes Insipidus

Whew!!! What a list. Thanks again Dr. James.


Luckily we rarely have to go down the whole list. Often the cause PU/PD will be picked up with initial blood and urine testing, plus or minus a few additional tests. On occasion initial testing will be negative and then the diagnostic work up becomes a little more challenging as the list would indicate. So if this happens, give you vet some slack – it may take a bit to diagnose.

How do I know if my pet drinks or pees too much??
PolyDipsia is defined as the consistent drinking of more than 100ml of water per kilogram of weight per day (>100mls/kg/day). PolyUria is defined as the consistent urination of more than 50ml of water per kilogram of weight per day (>50mls/kg/day). If you need help with the conversion of ml/kg/day – let me know I can make a new thread or we can do it by PM). Also you will notice that only half the water drank comes out as pee. Where did that other 50mls go? Insensible losses such as with stool, sweat, evaporation, tears, etc…

Why test, there isn’t anything I am going to do about it anyways?
While probably anybody that is still ready this, would never say this question, I get it a lot. So if you hear someone say it – this is what you can tell them. While these conditions may start out as just increased water consumption most will lead to severe, if not life threatening complications. Early detection can improve survivability, improve chances for a cure (if the disorder is curable such as infections), give the pet longer life expectancy, allow easier management and be less cost to the owner. This is a win-win solution! Early detection is the key. Also many of these conditions, even if not curable, can sometimes be simple and straight forward to manage early. For example, non-infectious kidney failure patients can have their life expectancy doubled by simple diet change. Pretty straight forward huh?

What else can I do to help be proactive?
Yearly blood and urine testing , especially on those dogs older than seven and cats older than ten. If younger – perhaps every other year. If funds are on the watch and we are only looking at PU/PD – then consider just a urine sample. If the urine is concentrated and otherwise normal, we have eliminated 25 diseases in one swoop! Wooohoo. Urine that is collected first in the morning is best because it has the best chance of being concentrated.

I hope this helps. Please feel comment on: whether or not this was helpful, if you would like me to write more of these, make them way shorter or keep the depth of knowledge the same, etc… Any constructive criticisms will be appreciated. Take care.
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Christopher A. Lee, D.V.M., C.V.L.S.
Promoting surgical options and pet comfort through the use of lasers.
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