Increased Thirst (Polydypsia)
There are a large number of causes of increased thirst (polydypsia) in pets. Besides the expected increase in thirst with hot days, exercise or change to a drier food, any pet showing polydypsia over 2-3 days should be examined by a vet. When making the appointment, try to bring along a fresh urine sample as a lot of information can be found by examining it.
- Kidney (renal) failure
- Cushing's disease (dogs)
- Medications e.g. cortisone, diuretics
- Urinary infections
- Liver failure
Kidney and Urine Tests
A quick examination of a urine sample can rule out the most serious and life threatening of diseases causing polydypsia, diabetes. Examining the strength of the urine (specific gravity) using a special instrument (refractometer) gives a good idea as to how well the kidneys are working. Spinning the urine down in a centrifuge, then collecting the sediment in the bottom of the tube and staining it with a special stain can show bacteria and abnormal cells.
Blood tests (biochemistry and full blood count) give an overall picture of a pet's health. An elevated kidney blood test ( BUN &/or Creatinine) suggests the pet is dehydrated and/or in kidney failure.
A pet has be down to its last 25% of normal kidney function before these blood tests rise.
Pets and humans can donate a kidney (and therefore be down to 50% total kidney function) and still lead a healthy life with no elevation of kidney blood tests or polydypsia.
If their remaining kidney becomes diseased, and loses over half of its ability to function, kidney blood test start to rise i.e. they have less than 1/4 (25%) of normal kidney tissue left in their body. In other words, we don't normally see elevated kidney tests in chronic renal failure until there is only 25% of healthy tissue left.
When there is 25-50% of healthy kidney function, kidney blood tests are often normal, but the urine may be dilute (low specific gravity). At this stage, the pet may be polydypsic as it is making too dilute a urine. The kidneys aren't doing their job of "recycling water" by sucking water out of the urine before it goes to the bladder to be voided. Their urine is dilute instead of concentrated. The brain realises it is losing more "water" than it should be from the body, so it activates the "thirst centre" in the brain which makes the pet look for water.
- A pet can lose up to 3/4 (75%) of its kidneys and still have a normal kidney blood test.
- Between 50-100%, the urine will still be concentrated (high specific gravity), and bloods normal.
- Between 25-50%, the urine starts to become dilutes (low specific gravity), and bloods normal
- Less than 25%, the urine is dilute and blood test abnormal.
It is important to check a urine sample as it can detect kidney failure long before a blood test. Regular testing of the urine specific gravity can be a great guideline as to the progression of the disease &/or response to therapy.