The urine specific gravity test in dogs is a test many dog owners may not be aware about, but it's run in countless veterinary office world-wide on a daily basis. If you never hear about this test before, rest assured you are not alone. Many vets run it without explaining it to dog owners and the first time dog owners hear about is when a dog's urine specific gravity test results are too high or too low. Following is information about the urine specific gravity test in dogs, how it's measured and what abnormal levels may mean by veterinarian Dr. Ivana Crnec.
The Role of Urine in Dogs
All the activities that a dog performs, from eating and breathing to running and jumping, are made possible by chemical reactions in its body cells. Wastes produced as a result of these reactions collect in the bloodstream.
For a dog to stay healthy, its urinary tract must filter, pull these wastes from the blood and excrete them. In addition to filtering the blood and excreting waste products and excess water, the urinary tract is also responsible for regulating the level of fluids and certain salts in the dog’s body, thus maintaining the acid-base balance.
Simply put, a dog's urinary tract consists of: a pair of kidneys, located on either side of the spine just under the last rib, the bladder, ducts that connect each kidney to the bladder and a duct through which urine flows when leaving the body.
Urine passes from the kidneys, where it is made, through the ducts to the bladder. When the bladder is full and its walls become stretched, the dog feels the need to pass urine, which goes through a special duct through which urine flows out.
Generally speaking, a healthy dog excretes about 0.5-2 pints or 0.25-1.0 liters of urine each day. More precisely, the daily urine output in dogs is 20 to 40 milliliters of urine per kilogram of body weight. However this number varies between breeds and individuals of the same breed.
Unfortunately, diseases and medical issues related to the urinary tract are not uncommon in the everyday practice. Diseases of the urinary tract can affect: the efficiency of kidney filtration, the quantity and quality of the urine, the frequency of the need to urinate, the control over when urination occurs.
How to Collect Urine from Dogs
The examination of a fresh urine sample is a diagnostic procedure that offers a plethora of useful information. Therefore, it is only natural to ask yourself how to collect urine from your dog.
Well, males are quite easy. Just clean a glass jar under hot water, then put on a rubber glove and catch a urine sample in the jar as the dog lifts his leg. For a female, it is more convenient to slip a clean saucer under her as she urinates and then transfer the urine to a jar.
Collecting a urine sample can be difficult with very small dogs. In that case, ask your veterinarian for a syringe so that you can immediately draw up a sample from a relatively clean surface.
It is highly recommended to take a sample a few moments after the dog has started urinating. This is to avoid contamination by bacteria from the opening where urine flows out of.
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It is also recommended to discuss with your vet the amount of sample he needs. The amount of sample needed depends on the tests he plans to perform. For instance, to do a urine stick test and measure specific gravity, your vet needs no more than a teaspoonful of urine.
Urine Specific Gravity Test in Dogs
Once the urine sample is collected and brought to the vet’s office it is time to examine it. The first on the examination list are the urine’s physical properties. The physical properties include all observations that can be made without a microscope and chemical reagents, like volume, color, odor, transparency and specific gravity.
The volume, color, odor and transparency features are simple and self-explaining, but what about specific gravity? Specific gravity is defined as the weight or density of a quantity of liquid as compared with that of an equal amount of distilled water.
In this case, simply put, the specific gravity of the urine is a comparison between the urine’s density and the water’s density. Since the specific gravity is determined by the number and molecular weight of the dissolved substances, the specific gravity of the urine can be defined as a measurement of the number of its particles. In a nutshell, determining the specific gravity of the urine gives a useful estimate of the urine's concentration.
How is the urine specific gravity measured? The urine specific gravity is most commonly determined by a refractometer. The refractometer measures the density of urine as compared to that of pure water. Basically, the urine contains substances that absorb different wavelengths of light. As the waves pass through the medium they bend. The refractometer captures how much each wave bends.
When using the refractometer, the procedure is quite simple:
step 1 – place a drop of urine on the glass
step 2 – close the protective cover
step 3 – read the values by looking through the viewfinder
step 4 – interpret the results
The urine specific gravity can also be measured with a urine test strip, but in that case the results are not very precise. Ultimately, the specific gravity can be determined with a urinometer. Unfortunately, the instrument requires a large sample volume and the results are not always quite accurate.
Interpretation of a Dog's Urine Specific Gravity Test Results
Under normal circumstances, in healthy dogs, the urine specific gravity may range from 1.001 to 1.060. Depending on the dog’s hydration status, the urine specific gravity varies throughout the day and between different days. For example, drinking excessive amounts of water just before the test or not drinking any water for several hours before the test will result in abnormal specific gravity values. However, these values are physiological.
Unfortunately, not all alterations in the urine specific gravity are physiological. Put as simply as possible concentrated urine suggests the dog is dehydrated, in acute renal failure or in shock. On the other hand, diluted urine usually suggests that the kidneys are not functioning properly. The urine may also be diluted as a result of:
certain medications – corticosteroids, diuretics, certain disease processes – some liver conditions, diabetes insipidus, cancers and pyometra.
Isosthenuria (USG of 1.008-1.012) indicates that the urine has been neither diluted nor concentrated by the kidneys. The condition is associated with chronic renal failure.
Luckily, more than for any other body system, the diagnosis of most urinary tract diseases can be made from careful examination of a fresh urine sample and from accurate information from you about your dog’s drinking and urinating habits.
This is because almost all urinary tract disorders lead to changes in the normal pattern of drinking and urinating. When the drinking and urinating patterns are changed, the urine’s features are also altered.