The Ins and Outs of Urinalysis
How do we collect urine from animals?
There are three typical methods for collecting urine from a pet.
- Free catch- This is the method used most often for urine collection because it is the least invasive. The urine is simply caught in a sterile cup while the animal is urinating. For dogs, we will either bring the dog outside to collect a sample, or we can send you home with a collection cup if the patient is unwilling to urinate for us at the clinic. Collection of urine for cats can be more complicated. Some cats will urinate in the clinic for us with gentle pressure on their bladders. Other times, we will recommend using Kit4Cat at home to collect a sample without stressing the cat. Kit4Cat is a litter replacement that repels urine and causes it to bubble up on top. The litter box is cleaned and emptied of regular litter. The sand from the Kit4Cat is put into the box and the patient urinates on it. A syringe provided in the kit is used to suction up the urine from the top of the sand.
- Cystocentesis- This is collection of urine directly from the bladder using a needle and syringe. Although it sounds intimidating, most animals tolerate this very well with minimal response to the procedure. This method allows us to more thoroughly assess the quality of the urine in the bladder itself, without concern about contamination from the fur and environment. If we are planning to culture bacteria from a urinary tract infection, we will want to collect the urine in this manner to get the most beneficial results.
- Catheterization- This method involves passing a urinary catheter up the urethra and into the bladder. This is uncommonly done because it can be uncomfortable for patients and there are simpler ways to collect a urine sample from most animals. However, a catheter may be used to collect a urine sample in patients who have a urinary obstruction or who are paralyzed and unable to empty their bladders on their own.
How soon do we need to look at the urine?
Ideally we would like to evaluate the urine sample within 30 minutes of collection. This minimizes the number of changes that occur to the urine outside of the patient and in the urine collection cup. If it is not possible to evaluate the urine this quickly, it should be kept in the refrigerator and evaluated within 24 hours. Urine that is older than 24 hours can still be evaluated, but changes may have occurred in the sample that make it more difficult to interpret.
Parts of the urinalysis:
- Color/cloudiness: The first quality of the urine that is assessed is its visual appearance. Normal urine is light yellow in color, although there can be some variation depending on hydration status and time of day. Clear urine may suggest that the patient is overhydrated or has a medical problem that prevents him/her from concentrating the urine appropriately. Dark urine may suggest dehydration or other substances in the urine that should not be there (such as blood or other pigments). We also assess the cloudiness of the urine, as cloudy urine is more likely to have cells or debris present within it.
- Specific gravity: This is a measurement of the concentration of the urine, or how “dense” it is. We measure specific gravity with a refractometer. If we are concerned about a dog’s ability to concentrate the urine (for example, with kidney disease), we may ask you to collect a first morning sample to evaluate the urine at its most concentrated. Cats are desert animals and their urine should always be concentrated, so time of day is less important for evaluation of their specific gravities.
- pH: The pH is one of several urinary parameters that is measured on a dipstick. This is a measurement of how acidic or basic the urine is. pH can change with diet and time of day, but it can also be affected by infections or other diseases. The pH of the urine is especially important for patients with a history of crystals or bladder stones.
- Protein: Normal urine should have minimal to no protein present in it. If there is protein in your pet’s urine sample, we may recommend a secondary test called a urine protein:creatinine ratio. This test lets us know if the amount of protein in the urine is significant or not. Some patients can have a small amount of protein in very concentrated urine and that can be normal. Significant protein in the urine should be further evaluated, as it can indicate problems with the kidneys or elsewhere in the body.
- Glucose: Glucose should not normally be present in the urine of dogs and cats. If there is glucose in your pet’s urine sample, diabetes is the primary concern. Sometimes stress can cause glucose to spill into the urine (especially in cats). Less commonly, kidney disease can also cause glucose to enter the urine.
- Ketones: Ketones are a byproduct of fat metabolism. They are most commonly seen in the urine of unregulated diabetics.
- Bilirubin: Bilirubin is produced by the liver and is not normally present in large amounts in the urine, although healthy dogs can have small amounts present. Large amounts of bilirubin in the urine can indicate liver disease or autoimmune disease.
- Blood: Blood in the urine either indicates bleeding in the urinary tract or passing of blood products into the urine from the body. There may be a small amount of blood in a urine sample due to collection if the urine was removed from the bladder using a needle. Other reasons for bleeding in the urinary tract include bladder stones, inflammation, infection, or tumors. The presence of blood in the urine is confirmed in the urinary sediment, as other molecules such as hemoglobin and myoglobin (from the blood or muscles) can cause this test to be positive on the dipstick.
- The urine sediment: In this stage of the urinalysis, the urine is spun down in a centrifuge to concentrate any cells or crystals that may be present. The sediment is then evaluated under a microscope. This can either be done manually or with new technology that uses a machine to spin and evaluate the urine. Our clinics are now using the Sedivue, which is a machine that images and analyzes the urine sediment using facial recognition technology. The veterinarian then evaluates and assesses the produced images. This technology allows us to evaluate urine samples more quickly, which increases the amount of information that we can get from them.
- Red blood cells- Red blood cells can be present in the urine in small numbers normally, but large numbers can indicate infection, stones, clotting abnormalities, trauma, inflammation, or tumors.
- White blood cells- Increased white blood cell count is indicative of inflammation or infection.
- Bacteria- Some bacteria can be present normally in a free catch sample due to environmental contamination. In a cystocentesis sample there should be no bacteria. Increased numbers of bacteria and white blood cells may indicate a urinary tract infection.
- Crystals- There are several different types of crystals that can form for different reasons. Pets who make crystals can also make bladder stones but these do not always correlate perfectly. Crystals can also be formed with urinary tract infections, liver disease, or certain toxins. Sometimes crystals will form while the urine is sitting in the collection cup, not in the patient. In this situation, we may wish to evaluate a urine sample immediately after production to eliminate this variable.
- Casts- Casts are collections of cells or protein that are formed in the shape of the kidneys’ tubules. These can be normal in low numbers or indicative of kidney dysfunction.
- Cells- There can be clumps of tissue cells in the urine sample normally. These come from the lining of the bladder and the urethra. If these cells look abnormal, more testing may need to be completed. Sometimes bladder cancer can be diagnosed in this manner.
- Sperm- Sperm may be seen in the sediment of intact male animals.
Overall, a urinalysis provides us with a lot of important information in both healthy and sick pets! Although it can sometimes be frustrating to collect (especially in cats), it allows us to diagnose problems that we cannot always find with just bloodwork and a physical exam. Some diseases like kidney disease can be found in urine before they cause clinical signs and bloodwork changes. This allows us to begin management and monitoring for your pet sooner.