Urinalysis

What is a urinalysis?

Urinalysis is a routine test that evaluates the physical and chemical properties of urine. It is used to assess the health of the kidneys and urinary system and can also help identify problems elsewhere in the body, including diseases such as diabetes mellitus.

Urinalysis is a valuable test in both healthy and sick animals and should be part of a pet's health assessment. If your pet’s urination habits change, a urinalysis can help identify the cause.

How is urine collected?

There are three main ways to collect urine in cats and dogs.

1. Cystocentesis. A sterile needle and syringe are used to collect urine from the bladder. The needle passes through the abdominal wall into a full bladder. Urine is then drawn directly into the sterile syringe.

This type of sample is ideal for assessing the bladder and kidneys and for detecting bacterial infection. The advantage is that the urine is not contaminated by debris from the lower urinary tract. 

However, this method is more invasive than other methods, and the bladder must be relatively full. Some pets may not lie still for collection. Ultrasound may help visualize the bladder and guide the needle, especially in larger or obese pets where the bladder cannot be easily felt (palpated).

2. Catheterization. A very narrow, sterile tube (catheter) is passed through the urethra into the bladder. The urethra is the tube that carries urine out of the body. A sterile syringe is attached to the catheter to draw urine from the bladder. Catheterization causes mild irritation to the urethra and may carry bacteria into the bladder. Female dogs and cats of either sex typically require sedation.

3. Midstream free catch. Urine is collected into a sterile container as the pet urinates normally. Ideally, the sample is collected midstream (partway through urination). This type of sample is often called a “free flow” or “free catch” sample. 

The advantages are that it is non-invasive, and the pet owner can collect the sample at home. However, collecting a midstream sample from some pets may be difficult. The urine is also more likely to contain debris and potentially bacteria from the urethra or the environment.

How is urinalysis performed?

There are four parts to a urinalysis:

1. Assess the urine’s appearance (color and turbidity, or cloudiness).
2. Measure how concentrated the urine is (urine concentration or specific gravity).
3. Measure pH (acidity/alkalinity) and evaluate the urine’s chemical makeup including the presence of any glucose (sugar).
4. Examine cells and solid material in the urine under a microscope.

Most of the analysis is done on whole urine (as it comes from the animal). To examine cells and solid material under a microscope, the solid contents, including cells and crystals, must be separated from the liquid. Urine is placed in a tube and spun at high speed in a centrifuge. This causes any cells and solid material to settle at the bottom. This material, called sediment, is collected, spread on a slide, and examined under a microscope.

What do changes in urine color and cloudiness mean?

• Normal urine is pale yellow to light amber and is generally clear to slightly cloudy. 
• Dark yellow urine may mean the pet needs water or is dehydrated. 
• Very pale yellow or clear urine suggests the pet is drinking a lot of water and urinating frequently. This may signal kidney disease or another disorder that affects the pet’s ability to produce concentrated urine. 
• Urine that is another color, such as orange, red, brown, or black, may contain substances not normally found in healthy urine. This may reflect injury or disease.

Increased cloudiness (turbidity) means there are cells or other solid materials in the urine. Examining the sediment shows what is present, and your veterinarian will determine whether it is a concern. Cloudiness is typically associated with blood, inflammatory cells, crystals, mucus, or debris.

What is urine specific gravity and how does it help detect disease?

Urine specific gravity measures how concentrated the urine is. Healthy kidneys can concentrate urine. Watery (dilute) urine may signal disease, depending on the pet’s water intake and hydration.

One of the kidneys’ jobs is to keep the body’s water level within a narrow range. If there is too much water in the body, the kidneys allow the excess to pass out in the urine. The urine then becomes more watery, or dilute. If there is a shortage of water (as in dehydration), the kidneys reduce the amount lost in urine. The pet then passes more concentrated urine.

Healthy animals may pass dilute urine at times during the day. A single dilute sample is not necessarily a cause for concern. If a pet continues to pass dilute urine, kidney disease or another disorder may be the cause. Further testing is recommended.

What is urine pH and why is it measured?

Urine pH measures how acidic or alkaline (the opposite of acidic) the urine is. The pH can change with diet but can also signal infection or a disease that affects how the body works (a metabolic disease). Urine in cats and dogs ranges from mildly acidic to mildly alkaline. Values outside this range are more likely to be associated with disease.

How is the urine’s chemical makeup tested?

The urine’s chemical makeup is tested using a dipstick: a small plastic strip with several test pads. Each pad tests for a different substance and changes color to show the amount present. The dipstick is dipped into the urine. After a short wait, the pad colors are compared with a chart to estimate how much of each substance is present.

What substances does the dipstick detect?

Protein. Protein in urine is called proteinuria. A small amount in concentrated urine may not be a cause for concern. However, protein in dilute urine should be investigated because it may signal developing kidney disease. A second test, called the urine protein:creatinine ratio, often helps determine whether proteinuria is a concern.

Glucose (sugar). Glucose should not be present in the urine of healthy cats and dogs. Large amounts usually indicate diabetes mellitus. Small amounts may also be found in pets with kidney disease.

Ketones. Ketones appear in urine when the body breaks down too much stored fat to meet its energy needs. This occurs most often with diabetes mellitus. It can also occur in healthy animals during prolonged fasting or starvation.

Blood. Blood in the urine usually means there is bleeding somewhere in the urinary system. Sometimes this is due to how the sample was collected. For example, small amounts of blood are often found in samples collected by cystocentesis or catheterization. Blood in the urine is also associated with bacterial infection, bladder stones, injury, or cancer. If it does not appear to be due to the collection method, further testing is recommended.

A positive result for blood can also occur with hemolytic anemia. In this disease, red blood cells are destroyed and release a protein called hemoglobin. Hemoglobin passes into the urine and causes the blood test pad to show a positive result, even without bleeding in the urinary system.

Occasionally, muscle inflammation or injury can cause a positive result for blood. Damaged muscle fibers release a protein called myoglobin, which is similar to hemoglobin. Myoglobin also causes a positive result, even without bleeding in the urinary system. A specific test for myoglobin can be done if muscle injury is suspected.

Urobilinogen. This test does not provide diagnostic information in veterinary patients.

Bilirubin. Bilirubin is a substance that is normally processed by the liver and excreted into the intestine in bile, where it then leaves the body. It is not found in the urine of healthy cats but may be found in small amounts in healthy dogs. Abnormal amounts in urine are associated with liver disease or red blood cell destruction (hemolysis) and should always be investigated.

Why examine the urine sediment?

Urine sediment is the material that settles at the bottom of the tube when a sample is spun in a centrifuge. It most often contains red blood cells, white blood cells, crystals, bacteria, and tissue cells from different parts of the urinary system. Small amounts of mucus and debris are often found in free-catch samples. Rarely, parasite eggs are found in the urine.

Red blood cells. Small numbers are often found in urine collected by cystocentesis or catheterization. Large numbers usually indicate bleeding. Causes may include bladder stones, infection, blood clotting problems, injury, or cancer.

White blood cells. Small numbers in a free-catch sample may not be a concern. In general, increased numbers indicate inflammation somewhere in the urinary system. This is often due to bacterial infection.

Bacteria. Bacteria and inflammatory cells in the sediment suggest a possible bacterial infection in the urinary system. Ideally, the urine should be sent to a laboratory for culture and sensitivity testing. This testing identifies the bacteria and helps determine which antibiotics may work if treatment is needed.

Crystals. There are many types of crystals, which vary in size, shape, and color. When found in urine, their meaning also varies. Some crystals help pinpoint a specific diagnosis. In more common conditions, such as bladder infection and bladder stones, crystals may help guide treatment; however, the type of crystal may not reflect the type of stone.

Crystals in the urine do not always indicate disease. Some form when a pet is given certain medications. Crystals can also form after urine is collected, especially if testing is delayed. Your veterinarian may examine a fresh sample right after collection to determine whether the crystals are a concern.

Tissue cells. Increased numbers of tissue cells are often seen in samples collected by catheterization. This alone is not a sign of disease. However, increased numbers can also occur with urinary tract inflammation, bladder stones, prostate problems in male dogs, or cancer. If the cells look abnormal, your veterinarian may prepare a slide for a more detailed cell examination (cytology). A pathologist may examine the cells if needed.

What is subclinical bacteriuria?

Subclinical (silent) bacteriuria means there are bacteria present in the urine sample, but no signs of a urinary infection, such as straining to urinate, urinating small amounts frequently, or blood in the urine.  

Certain conditions can weaken the body’s natural defenses, making it easier for bacteria to survive in the urinary tract. Some of these conditions, such as urinary sphincter weakness, may be treatable, while others are not. When possible, treatment of subclinical bacteriuria should include managing or correcting the underlying condition.

Antibiotics are usually not recommended for subclinical bacteriuria because they do not correct the underlying condition and may result in bacteria becoming resistant to antibiotics, making future infections much more difficult to treat. However, your veterinarian may recommend antibiotics in certain situations.  Subclinical bacteriuria is not believed to have negative effects if left untreated.