What is a urinalysis?
Urinalysis is a simple test that assesses the physical and chemical composition of urine. Abnormal results usually indicate that there is a disorder affecting the kidneys and/or urinary system. However, a urinalysis can also provide clues about problems in other organ systems, or may indicate the presence of a metabolic disease, such as diabetes mellitus. Urinalysis is necessary for a complete assessment of the kidneys and urinary system, and should be included in any thorough evaluation of a pet’s health status.
How is urine collected?
There are three ways to collect urine in cats and dogs. The best way is by cystocentesis, which involves passing a sterile needle through the abdominal wall into a full bladder and withdrawing the urine directly into a sterile syringe. The advantage of this method is that the urine is not contaminated by miscellaneous debris from the lower urinary passage that can interfere with the interpretation of the urinalysis. The cystocentesis method of urine collection is performed by the veterinarian in the clinic.
The second way to collect urine is by catheter, which involves passing a very thin sterile tube, called a catheter, up the urinary passage into the bladder and then collecting the urine by either allowing it to flow into a sterile container or by withdrawing it into a sterile syringe. This method of urine collection may be performed by either the veterinarian or veterinary technician in the clinic.
The last and simplest way to collect urine is by mid-stream “clean catch” or “free flow”, in which urine is collected into a sterile container as the pet urinates The advantage of this method, is that the pet-owner can collect the urine sample at home.
How is a urinalysis performed?
There are four steps to a urinalysis.
a) assessment of color and turbidity (cloudiness)
b) measurement of specific gravity (concentration)
c) measurement of pH (acidity) and analysis of the chemical components of the urine.
d) microscopic examination of the cells and solid material (called sediment) present in the urine
Most of the measurements are made on whole urine, but evaluation of the cells and solid material is performed on a “sedimented sample”. A sedimented sample is prepared by centrifuging the urine, which causes the solid particles (or sediment) to settle to the bottom of the tube. The sediment is then drawn off and examined under the microscope.
What do changes in color and turbidity mean?
Normal urine is pale yellow to light amber, and is generally clear to slightly cloudy. Urine that is dark yellow suggests the pet is dehydrated, while very pale yellow or clear urine indicates the pet is not concentrating urine well and may have kidney disease or another disease that interfere with urine concentration.
If the urine is any color other than yellow (for example orange, red, or black), it is likely that pigments are present in the urine, which may signal a serious underlying disease.
Increased turbidity is associated with the presence of blood, inflammation, crystals, mucus, and/or debris in the urine, and careful sediment evaluation is warranted to investigate the cause of the turbidity.
What is Specific Gravity and how does it help detect disease?
In simple terms, specific gravity is a measure of urine concentration.
One of the kidney’s jobs is maintain the body’s water level within fairly narrow limits. If there is an excess of water in the body, then the kidney allows the excess water to pass out in the urine, and the urine becomes more watery or dilute; if there is a shortage of water in the body (dehydration), then the kidney conserves water by reducing the amount of water lost in urine, and the urine that is passed is “thicker” or more concentrated.
A highly concentrated urine usually signals some degree of dehydration. The need to intervene with treatment will depend on what other clinical signs are present in the pet. If there are no other signs of illness, the pet may just need a drink of water. However, dehydration is a feature of many diseases, and the pet may need to be hospitalized for fluid therapy to correct the dehydration.
Normal animals may have dilute urine from time to time during the day, and a single dilute urine sample may not be cause for concern. However, if the pet is continuously passing dilute urine, it may indicate the presence of one of several diseases, and the veterinarian may want to investigate further. A common first step is to check the specific gravity of a first morning urine sample, since the first urine of the day is often the most concentrated. If the specific gravity of this sample is within acceptable limits, then there may be less cause for concern.
What is urine pH and why is it measured?
The pH of urine is a measure of how acidic or alkaline the urine is. The urine pH can be influenced by the pet’s diet, but it is often a reflection of the pet’s metabolic state, and it can also be an indicator of infection and underlying disease. Normal urine in the cat and dog ranges from mildly acidic to mildly alkaline. Extremes in urine pH are more likely to be associated with disease. For example, a pet that always has highly acidic urine may develop calcium oxalate stones; on the other hand, a pet that always has highly alkaline urine is more susceptible to bladder infections, and may develop struvite stones.
How is the chemical analysis of the urine performed?
The chemical analysis of urine is performed using a “dipstick”, which is a small strip of plastic with a series of individual test pads attached. Each test pad measures a different chemical component of the urine and changes color to reflect the amount of that substance in the urine. The dipstick is dipped into the urine and after a specified time interval, the color in the test pads is compared to a chart that translates the intensity of the color to an actual measurement.
What substances are detected by the chemical analysis of urine?
The presence of protein in urine is called proteinuria. Mild proteinuria in a concentrated urine sample may not be a cause for concern. However, any degree of proteinuria in dilute urine may be abnormal. The significance of proteinuria is often determined by doing a second test called the protein:creatinine ratio.
b) Glucose (sugar):
Glucose should not be present in the urine of normal cats and dogs. The presence of large amounts of glucose usually indicates the pet is suffering from diabetes mellitus. Smallamounts of urine glucose may be found in pets with some types of kidney disease.
Ketones appear in urine whenever there is excessive breakdown of fat to meet the energy needs of the animal. This occurs most frequently in diabetes mellitus, and less frequently during prolonged fasting and starvation.
d) Occult Blood:
A positive reading on the blood test pad usually indicates that there is blood in the urine, likely due to bleeding somewhere in the urinary system. A less common cause for a positive reading is a disease called hemolytic anemia, in which red blood cells are destroyed, releasing a protein called hemoglobin, which enters the urine, causing a positive color change on the blood test pad. An uncommon but occasional cause for a positive reading is muscle inflammation or injury, which causes the release of protein called myoglobin; this protein is very similar to hemoglobin and can cause the blood test pad to turn positive.
A detectable level of urobilogen in the urine indicates that the bile duct is open and that bile is able to flow out of the gall bladder into the intestines.
Bilirubin is a substance that is produced in the liver and normally excreted from the body in the bile. Bilirubin is not found in the urine of healthy cats, although it may be found in small quantities in the urine of healthy dogs. In some diseases, abnormally high levels of bilirubin may build up in the blood, and will be filtered out by the kidney, resulting in large quantities of bilirubin in the urine. The presence of bilirubin in the urine is often associated with liver disease or conditions involving red blood cell injury.
Why examine the urine sediment?
Many times there are details in the urinary sediment that are not found elsewhere in the urinalysis. Sometimes these details make a crucial contribution to the diagnosis. Therefore, examination of the urinary sediment should be included with every complete urinalysis.
What sorts of things can be found in a urinary sediment and what do they mean?
The most common things found in the sediment are red blood cells, white blood cells, crystals, bacteria, and tissue cells shed from the bladder and other portions of the urinary system. Parasite eggs and can also be found in urine, but this is very uncommon.
a) Red blood cells
Red blood cells may be found in small numbers in the sediment if the urine was collected by cystocentesis or catheterization. However, large numbers of red blood cells usually indicate bleeding, which may be caused by conditions such as bladder stones, infection, coagulation problems, trauma, cancer, etc.
b) White Blood Cells
Small numbers of white blood cells in a “free-catch” sample may not be significant, but in general, an increased number of white blood cells indicates inflammation somewhere in the urinary system. Inflammation is often secondary to bacterial infection.
c) Tissue Cells
Increased numbers of tissue cells often indicate underlying inflammation, bladder stones, or prostate problems (in the male dog). If the cells appear abnormal, there may be concern for cancer, especially in the older pet, and a special preparation of the urinary sediment, called a cytological preparation, may be requested to allow a more detailed examination of the tissue cells.
Crystals are often identified by their shape and color. Certain types of crystals are associated with specific disorders, and if these crystals are found in a pet’s urine, the veterinarian may advise doing additional tests. Conditions such as liver disease, anti-freeze poisoning, or bladder or kidney stones may be suspected if the appropriate type of crystal is present.
Crystals in the urine do not always indicate disease; some crystals are found because of medication the pet is receiving, and some crystals form in urine after it is collected – this usually occurs if the urine is stored incorrectly, or if there is a long delay between the time the sample is collected and the time it is examined.
Bacterial infection is a common cause of inflammation of the bladder and sometimes of the kidneys. The presence of both bacteria and inflammatory cells in a urine sediment usually indicates that there is bacterial infection somewhere in the urinary system. If a bacterial infection is identified, the veterinarian may want to send the urine to the laboratory to find out what kind of bacteria are present and which antibiotic is best suited to treat the infection.