To Pee or Not to Pee – That is the Question
When I was a senior veterinary student, our dermatologist at UT was on maternity leave. Normally, we had one rotation with her, two rotations in general medicine, and one rotation in neurology. Since Dr. Schmeitzel was off clinics, I had three medicine rotations, and my extra one was with Dr. Leland Thompson. He loved endocrinology, and we saw tons of cool endocrine cases (you know that is probably why I love endocrinology to this day). Dr. Thompson was a quirky man, and he called urine “the golden juice of life.” Kinda gross, but you know, there is a lot of truth in that.
The urinalysis can give information about the urinary system as well as other systems. When we perform a urinalysis, there are actually four things that we evaluate. First, we look at the physical characteristics of the urine. Then, we evaluate the specific gravity followed by urine chemical properties and microscopic examination of the urine sediment.
Before we go too far, there are three ways that urine can be collected. We can use a free catch sample, and just like the name sounds, this sample is caught mid-stream during normal voiding. If we ask you to do this at home, you can buy an inexpensive soup ladle at a dollar store, and it works great to collect a urine sample. This is often the easiest way to collect urine, but it can be contaminated since it passes through the distal urethra, genital tract, and external skin. Urine can be obtained through a catheter. This sample can be contaminated as well. Lastly, urine can be obtained by cystocentesis, which means the urine is collected directly from the bladder with a needle and syringe. I know that sounds terrible, but honestly, most dogs and cats object less to cystocentesis than to having their blood drawn.
Back to performing our urinalysis. When we evaluate the physical characteristics, we look at the color. Normal urine should be light yellow to straw in color. If it is red, it contains blood. If it is brown, it may have blood, hemoglobin (a breakdown product of blood) or myoglobin (a breakdown product of muscles). We look at the clarity of the urine. Clear is good. Cloudy or turbid suggests increased numbers of cells, which are often caused by infection. Odor can be important, too. Strong odors can be associated infection or dehydration.
Specific gravity is actually the ratio of the weight of a volume of liquid to the weight of an equal volume of distilled water. Urine specific gravity is measured on a refractometer for veterinary species. A drop of urine is placed on the daylight plate of the refractometer and pointed in the direction of a bright light. The number will be reported as 1.0XX. Urine that is maximally concentrated will have a specific gravity of 1.035 or above. Urine that is not maximally concentrated will be in a range of 1.013 – 1.034. If urine specific gravity is between 1.008 – 1.012, the pet likely has primary kidney disease, and urine that has a specific gravity of 1.007 or lower is being actively diluted because the pet is drinking water excessively.
Now, we will talk about urine chemistries. These are evaluated with a urine dipstick, and we read color changes on pads. These color changes occur within a certain time after urine is applied to the pad, and this has historically been read by a person. There are several analyzers that now read these test strips with great accuracy.
Urine pH is often acidic in dogs and cats, but this is dependent on diet, medications, or disease. Dogs and cats with urinary tract infections are more likely to have alkaline urine. Urine pH will affect the presence of crystals in some urine samples. In an alkaline pH, struvite crystals are more likely to form, but in an acidic urine sample, calcium oxalate crystals are more common.
Protein, primarily albumin, is evaluated in urine. Normally, very low quantities are present. When protein is observed, it can be associated with primary kidney diseases, fevers, seizures, or any type of inflammation/hemorrhage/infection in the genitourinary tract. We will often perform a test called a protein:creatinine ratio to more accurately assess the true amount of protein being spilled into the urine if the protein is present because of primary kidney disease.
Glucose is typically not seen in urine. The most common reason to have glucose in the urine is diabetes mellitus, but cats can have a transient increase in urine glucose from stress. There are also certain diseases of the tubular portion of the kidneys that can cause glucose to be spilled in the urine even though serum glucose is normal.
Ketones are chemicals in your body that are produced when fat is used as the energy source instead of carbohydrates. They are normally not detectable in urine. When present in the urine, they are usually seen in ill diabetic patients. They can also be seen in starving patients.
Bilirubin is a breakdown product of hemoglobin. If bilirubin in high in the urine, serum bilirubin levels should be checked. The three reasons that bilirubin can be seen in the urine are destruction of red blood cells, severe liver disease, or obstruction of the bile duct into the GI tract.
The pad on the urine dipstick that evaluates the presence of blood in the urine actually reacts to free hemoglobin (associated with destruction of red blood cells), free red blood cells (true blood in the urine), and myoglobin (seen following severe muscle damage). The most common reason for a positive reading for occult blood is true hemorrhage in the urinary tract, and a sediment examination should always be performed to further evaluate this abnormality.
Now, we will move on to the urine sediment. This part of the urinalysis is performed with a microscope. We look for the presence of red blood cells or white blood cells in excess. Bacteria can be seen with infection, but bacteria are much harder to find in really dilute urine. So, in patients at high risk of infection (diabetics, immunosuppressed patients, cancer patients), we will submit a sample for culture even if bacteria aren’t seen on the sediment. Crystals can be seen on the sediment. Struvite crystals are often seen with infection. Calcium oxalate crystals can form because of excess calcium in the body or because of excess of secretion of calcium with normal levels in the body. These crystals are the hardest to keep from coming back. Ammonium biurate crystals are seen in Dalmatians and English bulldogs normally, and if seen in other dog breeds or any cat breed, they suggest liver disease. Sperm can be seen normally in intact male dogs.
Earlier, I mentioned that strip analyzers are now available to read dipsticks. There are also sediment analyzers to evaluate urine microscopically. They contain microscopes inside of the unit, and they take multiple pictures of the urine sediment and print them so that they can be evaluated at any time. Cool, huh? Below is a picture of our urine analyzer. We have been using it for almost two months, and if you ask me or Jane, it is really doing a fantastic job of evaluating urines for us.
As I close this blog, I think the answer to my rhetorical question is definitely to pee! It answers lots of questions!