Why Is My Dog's Urine Specific Gravity Abnormal ?

Why Is My Cat's Urine Specific Gravity Abnormal ?

To see what normal blood and urine values are for your pet, go here

For an explanation of causes of most abnormal blood and urine tests go here

To see how tests are often grouped, go here

Ron Hines DVM PhD

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Specific Gravity Of Your Pet's Urine

SpGr, USG

Determining the specific gravity of your pet’s urine is the way veterinarians judge how concentrated it is.

The higher the SpGr number, the more concentrated your dog or cat 's urine is - the lower the number, the more dilute it is. Pure water has a specific gravity of 1.000. If your pet’s kidneys are healthy, its urine specific gravity will be constantly changing - but its kidneys will do their best to keep its SpGr between 1.015 and 1.060.

The number will go up when your pet is dehydrated and go down after it drinks water. It will tend to be highest just after it gets up in the morning.

Reasons Why Your Pet’s Urine Specific Gravity Reading Could Be High :

A normal or high urine specific gravity usually indicates that your pet’s kidneys are working well. But it can also be high if your pet has developed diabetes that has allowed sugar to leak into its urine or when the protein content of the urine is abnormally high.

When your pet’s urine specimens repeatedly test high for SpGr, it is often a sign that your pet is not consuming enough fluids throughout the day. That can be a major side effect of maintaining pets (particularly cats) on dry petfood. You see, many pets do not drink sufficient water even when you keep a bowel of water always available to them. Those pets stay marginally dehydrated producing high SpGr urines. They are probably at a greater risk of developing kidney and bladder stones because the salts that form those stones fall out of solution to form crystals (oxalate and struvite) much faster in concentrated (high specific gravity) urine than in dilute urine.

(Chronic, mild dehydration that could elevate your pet's urine specific gravity is thought to be most common in cats consuming dry cat foods. These signs of dehydration, as in humans, can be nebulous (vague) and only significant over time [ref1 , ref2, ref3]. More severe dehydration can accompany any disease in which apathy or reduced mobility occurs.)

Other causes of dehydration that will elevate your pet's urine specific gravity are vomiting, diarrhea, heatstroke and fever.

Reasons Why Your Pet’s Urine Specific Gravity Reading Could Be Low :

Persistently low urine specific gravity in your dog or cat is more common, and potentially more worrisome than high specific gravity. In older pets, it is often the first sign (along with increased water consumption = polydipsia) that their kidneys are failing. Persistently low urine specific gravity is called isosthenuric urine (1.008-1.012). That urine is more or less the same concentration (osmolality) as the pet’s blood plasma and it means that the pet’s kidneys can neither concentrate nor dilute urine once it has initially formed. Those pets are usually azotemic as well. You can have a look at a chart that shows how veterinarians try to sort out the causes of dilute urine here.

A 2015 study found that healthy cats should have a urine specific gravity of 1.035 or greater. That number decreased slightly as the cat's aged and was slightly lower in female cats. Urine submitted to outside laboratories registered slightly higher values than those run with a refractometer at the animal hospitals. In older (≥ 9yrs) cats, lower-than-normal urine specific gravity results should be followed by a blood BUN assay to check the cats for kidney disease. (ref)

Unspayed adult female dogs and cats with a uterine infection (pyometra) often show increased thirst and abnormally dilute (low SpGr) urine. That is due to toxins released by bacteria in their infected womb.

A number of conditions can cause your pet’s blood calcium levels to be too high. You can read about them here. That higher-than-normal blood calcium level can interfere with the ability of your pet’s kidneys to concentrate urine (ie low SpGr).

Dogs and cats with failing livers (hepatic insufficiency) can also produce low specific gravity urine. Those pets will probably also have abnormal blood albumin, bile acids, cholesterol and liver enzyme tests (ALT, AST, AP, bilirubin). Veterinarians are uncertain as to why liver problems affect the SpGr of your pet’s urine.

Overactive Adrenal glands (Cushing’s disease = hyperadrenocorticism) or corticosteroid medications often cause low specific gravity urine in dogs. There is less of that effect in cats. Their urine becomes more dilute because these pets drink more.

Hyperthyroid cats often drink more and produce more dilute urine. It is not clear why that is.

Low blood potassium can also be associated with dilute urine.

Under active adrenal glands (Addison's disease = hypoadrenocorticism) can also cause your pet’s urine to be too dilute.

Diabetes insipidus, a rare form of diabetes, will also cause pets to produce a urine with low specific gravity. This disease is usually due to a failure of your pet’s pituitary gland to produce the hormone ADH.

Complementary Tests That Come To Mind :

Older thin cats run FreeT4 for hyperthyroidism

CBC /WBC and blood chemistry panel, ACTH stimulation test, dexamethasone suppression test, urine cortisol:creatinine ratio

.................... DxMe