By Dr. Laura Hady
While I believe the physical exam is the cornerstone to an accurate diagnosis, I also think that the urinalysis is an excellent screening test. A urinalysis not only provides information about the bladder, such as whether an infection is present, but it also lets us know if your pet’s kidneys and hormonal systems are working properly. Your veterinarian may obtain the urine at the office by sticking a needle directly into the bladder (cystocentesis) or have you to collect it at home by placing a plastic container under your pet as it is urinating (free catch method). The following discusses some of the indicators found in this powerful test.
- How are the kidneys working as a filter? The kidneys filter all of the blood volume in a day, with 99 percent being returned to the blood, and 1 percent released in the animal’s urine. The urine specific gravity indicates how concentrated, or dense, the urine is at a given time. The urine should be most concentrated in the morning, so if the urine concentration is low, the body is losing too much urine, indicating the kidneys or the adrenal gland may not be working properly. If it is too high, the animal may be retaining water, which happens in dehydration. Proteins are very large molecules and have a difficult time passing through the fine filtration of the first part of the filter called the glomerulus. If there are high levels of protein in the urine, this could be a sign of an infection, blood in the urine, muscle proteins, or protein from the blood, which indicates kidney disease.
- Is it abnormal to have glucose and ketones in the urine? Yes, glucose in the urine (glucosuria) is abnormal and occurs when blood glucose levels exceed a maximum threshold of 200 milligrams per deciliter. (Normal is 60-120 milligrams). This will alert your veterinary staff that your pet has diabetes mellitus even before the full blood chemistry panel results are completed. Having glucosuria makes your pet more susceptible to having bladder infections as glucose is a readily available source of energy for bacteria such as E. coli. Ketones in the urine (ketonuria) can be present if your pet has gone a long time without eating. Ketonuria in a diabetic animal can reveal a severe abnormality known as diabetic ketoacidosis (DKA). Animals with DKA will need to be hospitalized and receive intravenous fluids, insulin, and supportive medications such as anti-vomiting medication.
- What is the normal acidity of my pet’s urine? The pH level tells us the acidity of the urine. Animals that eat more meat have more acidic urine. For cats, the pH is about 6.3-6.6, while the pH for dogs is around 7-7.5. Herbivores, such as hamsters, have a higher pH (more basic) because they eat mostly plants. Some bacteria that cause urinary tract infections can release ammonia-like products, which can raise the pH. When the urine pH becomes too high, crystals such as struvite are formed. Crystals in the urine can lead to stones in the bladder. Some crystals, such as calcium oxalate, form at a lower pH, and may also lead to stone formation. Your veterinary staff may treat an existing infection with antibiotics and also use special diets to bring the pH into the more normal range.
- Why would my pet’s urine contain bilirubin? Bilirubin is the yellow byproduct of red blood cells and is normally excreted by your pet’s liver. A small amount in the urine is considered normal. However, high levels can indicate liver disease or an immune system problem where the body attacks red blood cells and causes them to break down quickly.
- Why should the urine sediment be looked at under a microscope? This is the part of the urinalysis that I find most fascinating. Urine sediment is the material that settles to the bottom of tube after urine is spun in a centrifuge. (A good analogy would be the wine sediment that contains impurities and sometimes collects in the bottom of a bottle.) Once the clear urine at the top is poured off, we can see the sediment containing impurities on the bottom. At this point, a stain is added and mixed with the sediment, and a drop is added to a microscope slide. In this drop of urine sediment, the veterinary staff is able to observe the abnormal presence of red blood cells indicating inflammation, white blood cells and bacteria indicating infection, or crystals, which can indicate bladder stones or an abnormal pH to your pet’s urine.
I hope you have learned a little something of the significance of examining your pet’s urine. I will often use the results of a urinalysis as a stepping stone to other diagnostic test,s such as blood work, X-rays, and abdominal ultrasound. That is why it is so important to help veterinary staff get your pet’s urine sample if your pet is having difficulty urinating, urinating in the wrong location, urinating when sleeping, or having abnormally colored urine.
