Why is my dog drinking and urinating more recently?

Drinking and urination are inextricably related. Most dogs will drink between 50 and 100 ml/kg/day or less and produce 30-50 ml/kg/day or less. Urine production over 100 ml/kg/day is considered excessive. Excessive drinking (polydipsia (PD)) and excessive urination (polyuria (PU)) in dogs usually indicates a significant health concern.

Because there are many possible causes of PU/PD, laboratory evaluation is needed. Often, we can identify the problem with routine blood chemistry evaluation, complete blood count, and a urinalysis. These tests help determine if the problem is in the kidneys, pancreas, or elsewhere in the body. In many cases, we must evaluate further.

Some of the causes of PU/PD are hormonal diseases. The most common problems are Cushing’s disease and diabetes mellitus. In Cushing’s disease (hyperadrenocorticism) there is usually a tumor of the pituitary or adrenal gland, which causes the adrenal gland(s) to produce too much cortisol (steroid). The cortisol acts in the kidneys to produce more urine that is dilute.

Diabetes mellitus is a pancreatic disease. In the dog, there is an immune mediated destruction of the cells that produce insulin. This results in very high blood glucose. The kidneys are not able to reabsorb the glucose from the urine. Water follows the glucose into the urine causing increased urine production.

Less commonly, diabetes insipidus occurs. This hormonal disease is related to antidiuretic hormone produced in the pituitary gland. Either the pituitary gland does not produce the hormone, or the kidneys are unable to respond to the hormone. Without antidiuretic hormone, the kidneys are not able to concentrate the urine so very dilute urine is produced.

Some problems are directly related to the kidneys. In chronic kidney disease, the kidneys become functionally smaller and often physically smaller. Because of the decreased capacity to filter the blood and produce urine, the kidneys are unable to concentrate or actively dilute the urine. This type of problem is usually not apparent until late in the disease process, after about two thirds of the kidney function has disappeared.

For similar reasons, kidney infections (pyelonephritis), some kidney tumors, and some stages and causes of acute kidney failure will also sometimes produce unconcentrated urine.

There are also disease processes that affect the kidneys secondarily. During post-obstructive diuresis, the kidneys will produce more urine to help clear the toxins from the blood that could not be removed while the urethra was blocked. Hypercalcemia (too much calcium in the blood) will cause the kidneys to produce dilute urine. Hypercalcemia causes include kidney disorders, hormonal disorders, nutritional derangements, bone diseases and cancers.

The brain must also be considered for reasons for excessive drinking. Problems with the thirst center can cause a dog to drink excessively. These problems can include inflammation, tumor, developmental problems, and injuries. We sometimes see dogs with what is referred to as psychogenic polydipsia. With this problem, the dog drinks more than it needs for behavioral reasons.

We must never forget to consider causes from human interaction. Many medications will cause dogs to drink and/or urinate excessively. The most common drugs include steroids, some hormones, phenobarbital, diuretics and fluids. Supplementing the diet with salt will also cause many dogs to produce more urine.

By no means is this list of causes complete. Most of these problems affect the kidneys and or urine production directly. As a result, if water is limited, severe dehydration and other life threatening, secondary problems can occur quite rapidly. Therefore, do not limit your dog’s water until you identify the underlying problem.

If your dog seems to urinate and drink excessively, please have it evaluated by a veterinarian. If left untreated, many of these disease processes will have life threatening consequences. Even with treatment of some diseases, the best we may hope for is an improved quality of life for a time. Other diseases are not life limiting and/or respond to treatment.

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