Cat & Dog - Excess Thirst and Urination

What are the causes of increased thirst and urination?

These are non-specific clinical signs and can be caused by many different conditions and diseases.  For example, a sudden hot spell of weather can result in active animals appearing to drink excessively, although this is a normal reaction to the increased temperatures.  Thirst and urine production are obviously connected and it is usually the production of excess dilute urine (polyuria) that results in compensatory increase in water consumption (polydipsia).  Occasionally the situation is reversed and the condition is one of increased water intake resulting in the production of large volumes of dilute urine.

What causes increased thirst?

The common causes of increased thirst include:

• Conditions associated with the urinary and reproduction systems.  These include kidney failure, infection of the kidney or bladder and infections of the uterus (e.g. pyometra)
• Liver disease
• Fever, pain and certain electrolyte imbalances may also result in increased thirst and urination.
• Endocrine or hormone related conditions including hyperadrenocorticism (Cushing's syndrome), hypoadrenocorticism (Addison's disease), hyperthyroidism, diabetes mellitus (sugar diabetes) and diabetes insipidus (drinking diabetes).
• Behavioural problems can very occasionally be responsible for these signs

From these possible causes how is a definite diagnosis made?

As with any veterinary problem, on initial presentation, a careful clinical examination and, just as importantly, an accurate history, is imperative.  Certain diseases are more common in certain species (i.e.dogs, cats).  In addition, the specific history of the pet including a list of any medication and supplements recently received is very helpful.

Age, diet and general condition of the pet often also supply vital clues.

Are there any specific laboratory tests available?

There are many tests available that may be helpful but first screening tests should include a full urine analysis together with routine blood tests which involve a complete blood count (CBC) and serum biochemistry.  These screening tests may not only provide information regarding the cause of the increased thirst and urination but also sometimes uncover other problems which may need treatment.

Urine analysis is a simple procedure which gives an indication as to the concentration of the urine, its acidity or alkalinity (pH), as well as the presence of red and white blood cells which may be indicative of inflammation or infection.

For example, diabetes mellitus (DM) or sugar diabetes is often picked up from a simple urine test.  If accompanied by a finding of increased serum glucose (blood sugar) this is supportive of a diagnosis of sugar diabetes (DM) which would account for the increased thirst and urination.

Similarly, the urine test can provide information regarding protein and bilirubin (a pigment associated with liver disease) and these results can then be further verified by the blood test.

Ideally a urine analysis should always accompany any routine blood tests involving serum biochemistry.

Serum biochemistry profile

Serum contains many substances including fats (lipids), glucose, proteins and various metabolic waste products.  The amount of these components of the serum together with values for electrolytes and enzymes associated with processes involving the liver, kidney and pancreas can also be measured.  These results, taken in conjunction with the results of the urine analysis may give a pointer to the cause of the increased thirst or urination, or if the biochemistry results are within the normal range, indicate that the presence of certain diseases is unlikely.

Complete blood count

A complete blood count (CBC) measures the total numbers of red and white blood cells together with platelets and can also indicate specific cellular characteristics.

The white blood cell count is particularly important in cases of increased thirst and urination.  Inflammatory or infectious conditions usually result in increase in white blood cell numbers.  For example, Cushing's syndrome is associated with an increase in white blood cells while hypoadrenocorticism (Addison's disease) may result in increased proportions of certain white blood cells (such as lymphocytes and eosinophils).  Examination of the red blood cells may give an indication of the presence of anaemia.  This can be associated with certain types of kidney disease, which again would give an indication of the reasons for the increased thirst and urination.

Will further testing be required?

This depends entirely on the results of the initial screening test.  In most instances the initial test provides either a specific diagnosis or will indicate the need for further investigation.  For example, if the original tests are suggestive of Addison's disease (hypoadrenocorticism) the condition will need to be confirmed by an ACTH stimulation test.  If liver problems are suspected, the level of serum bile acids may have to be measured, often together with imaging studies of the liver including ultrasound and radiographs (x-ray).

Water deprivation tests

If the initial screening tests have ruled out kidney disease, and the reason for the increased thirst and urination is still unclear, a water deprivation test may be necessary.  Normally the kidneys will concentrate the urine to conserve fluid if faced with a situation of reduced fluid intake.

For this test the patient is closely monitored, deprived of fluids for a specified period and the state of hydration and urinary concentrating ability evaluated.  The test ends when the subject either shows signs of adequate urine concentration or is beginning to dehydrate.

If the patient fails to concentrate the urine, ADH tests may be necessary.

Anti-diuretic hormone (ADH) tests

If it is clear that the kidneys are not concentrating the urine adequately during the period that water is deprived, tests may be extended to include the use of anti diuretic hormone (ADH).  This is a naturally occurring hormone that acts on the kidneys to cause the concentration of urine.

Interpretation of the results

Water deprivation tests are very useful when evaluating increased thirst and urination.  The interpretation of the results falls into three categories:

1. If the screening tests are normal and the animal concentrates the urine during the water deprivation test it is likely that increased thirst and urination are related to behaviourally increased water consumption or external factors such as increased ambient temperature as mentioned previously.
2. If the patient fails to concentrate the urine during the water deprivation test period but does so after administration of ADH the cause is likely to be related to central drinking diabetes.  This is caused by a failure by the brain to produce ADH hormone.
3. If the patient failed to concentrate urine during the water deprivation test and also fails to concentrate in response to administration of ADH then the cause is probably related to nephrogenic (kidney related) diabetes insipidus.  This indicates that the kidneys are unable to respond to the ADH or that there are physical factors within the kidney tissue preventing concentration occurring.

Please do contact us if you wish to discuss the matter further.