Excessive Thirst and Urination

[Tami]

 Excessive Thirst and Urination
    
When your pet tanks up at the water bowl, is it really a problem? Or is it merely a response to a hot environment or a dry diet?

When excessive thirst or polydipsia is associated with the production of excessive amounts of urine or polyuria, we may safely assume that something is amiss. But the problem could be either behavioral or physical. And which comes first, increased thirst or increased urination? The problem, in fact, might be excessive urine production that drives greater thirst and water consumption.

The diagnostic approach to PU/PD (polyuria/polydipsia) may be simple and straightforward, but often it is not. The veterinarian must be certain that any changes in urination habits are caused by greater than normal urine output, rather than urgency and difficulty urinating or loss of bladder control. Verifying the problem, therefore, is extremely important.

After collecting a detailed history, the veterinarian may wish to observe the pet's urination, so that he or she can assess normalcy and completeness of emptying. The volume and quality of the urine produced is of paramount importance, since the urine's specific gravity directly reflects the concentration of the urine and, indirectly, the volume of urine produced. If the urine sample is very dilute, it will have a low specific gravity, indicating that excessive urine production is probable. However, if the pet produces urine that is particularly well-concentrated, then excessive urine production is not likely.

A urine specimen collected in a sterile fashion, especially by needle procedure or cystocentesis, is frequently used to complement the information provided by a voided specimen. The presence of abnormal cells or protein levels in the urine may suggest urinary infection as the cause of the change in urination habits, rather than too much urine.

Another important step in getting to the bottom of this problem is the owner's measurement of the patient's average daily water consumption. Most dogs and cats will consume 20 to 70ml/kg (1kg = 2.2 lbs) in a 24-hour period -- this figure takes into consideration both free water consumed and dietary water, which is higher in canned foods. Pet owners will be asked to measure carefully the pet's water consumption for three to four consecutive days, and present an average. This can be a challenging task if there are multiple animals sharing a bowl, or if the pet has access to a pool or pond. It is also important to make toilets and other fountains off limits during the test time.

Of course, if these tests reveal no evidence of elevated water intake or no suggestion of increased volume of urine produced, then the problem should be re-defined as something other than PU/PD.

Upon verifying that PU/PD is the problem, the veterinarian will need to determine whether it's thirst (polydipsia) or urination (polydipsia) is the primary problem. Primary polyuria is more common in dogs and cats, and is commonly associated with problems in the kidneys' urine concentrating mechanism. Diseases such as kidney failure, diabetes mellitus, hyperadrenocorticism (Cushing's Disease) and hyperthyroidism are commonly presented with these signs. Any history of medication use is reviewed, especially if corticosteroids or anticonvulsants have been recently prescribed, as these medications are likely to produce PU/PD.

The systemic balance between water intake and water output is controlled largely by the action of the antidiuretic hormone (ADH) on the kidneys. In kidney failure, the kidneys become less responsive to the normal hormonal effects of ADH and they are further challenged by excessive waste products in the bloodstream; both of these problems can contribute to primary polyuria. Certain systemic bacterial infections, especially those associated with uterine or kidney disease, may inhibit the action of ADH at the kidney, as may corticosteroid hormones, either produced naturally or given as medication. The end result is that the dog or cat urinates too much, and drinks excessive water to avoid becoming dehydrated.