September 19, 2016June 29, 2019
Concerned about your dog or cat’s urinalysis? Last time, you learned all about blood. Now, let’s learn all about pee! I promise, reading this article will beso much more funthan cleaning up a wet spot on your carpet when your petjust can’t cross its legs and hold its bladder any longer.
If your veterinarian is concerned aboutthe health of your pet’s urinary tract, or if your pet has suddenly begun urinating excessive volumesand drinking greatamountsof water (suggestive ofpolyuria andpolydipsia, respectively), analyzing a urine sample (i.e. a Urinalysis) is likelyin order.
- Collection Method: How does one obtain a urine sample from a pet? There are three means of collection: free-catch (where someone with a bowl or ladle catches a mid-stream urine sample from a pet when it’s urinating outside, or when urine is gathered from a kitty’s litterbox), catheterization (in which a urinary catheter is sterilely placed through a patient’s urethra into the urinary bladder), or cystocentesis (which involves a small needle on a syringe directed through the skin of the abdomen directly into the urinary bladder by your vet). Cystocentesis is the “cleanest” means of collection as it removes the potential for contaminates to enter the urine sample, unlike a free-catch sample which can allow fur, grass, dirt, or fecal matter to fall into the sample during collection (altering the results). (Although the thought of having a needle directed into your pet’s abdomen may sound a little scary, it’s very similar to the use of a needle for bloodwork or vaccines.)
- Color / Transparency /Odor: Depending on how concentrated ordilute your pet’surine is at the time of collection, normal urine should be a transparent pale yellow to a darker yellow and should have a typical “urine” odor. Cloudy or white/green urine, especially with a strong odor, is often an indication of a urinary tract infection while red-tinged urine indicates blood and orange urine can be a sign of excessive bilirubin in the urine (as due to liver disease or red blood cell destruction).
USG: Urine Specific Gravity assesses how concentrated your pet’s urine is (i.e. how many molecules of salt and waste products are dissolved in the water portion of urine as appropriately processed by the filtration action of the kidneys). A dog’s kidneys should be able to concentrate urine above USG 1.030, while cats should be able to concentrate over USG 1.035. However, a one-time reading may not be very helpful, so your vet may wish to recheck serial urine samples for a true USG assessment. For instance, if your happy-go-lucky Labrador guzzled an entire bowl of water right before you drove to the vet’s office, then his USG may be very low due to water dilution. However, if a first-morning urine sample was collected before he drank any water, his USG may be well over 1.030 since it is more concentrated. Conversely, one would expect a very dehydrated animal to have a very high USG; if not, then the animal likely has kidney disease, causing the kidneys to leak too much water into the bladder instead of preserving it in the bloodstream where it is needed during periods of dehydration.If your dog or cat’s USG is consistently low (indicating dilute urine), your vet may be concerned about your pet’s kidney function (remember, one of the roles of the kidneys is to remove toxic waste products out of the bloodstream and concentrate all those toxins into urine). USG is analogous to BUN and creatinine on bloodwork. However, with early kidney disease, changes in USG can be perceived prior to changes on bloodwork. Over three-fourths (75%) of kidney filtration units called nephrons must be diseased before alterations in BUN and creatinine occur (known as azotemia); however, when only two-thirds (66%) of nephrons are damaged, USG will begin to decrease (known as isosthenuria when USG is between 1.008-1.012). By assessing USG early in kidney dysfunction, this allows your pet to begin prompt management to slowthe progression of kidney disease as deemed appropriate by your veterinarian (i.e. a prescription diet for kidney health, supplements, fluid therapy, etc.) as well as alert everyone to schedule more frequent rechecks.- Dipstick: Tiny drops of urine are placed on a test strip called a dipstick to assess the urine’s pH (acid-base status) and to detect the presence of various molecules in the sample. Color changes on the test strip denote the presence of the corresponding molecule.
- pH: First, some terminology: alkaline urine has a higher pH than normal while acidic urine has a lower than normal pH. As explained, pH measures the acid-base balance of the body. The body of a living organism is simplistically described as a vat of thousands of chemical reactions across every organ, tissue, and cell that need a certain pH in orderto occur. An elevated pH resulting in alkaline urine can occur following a meal (known as post-prandial alkaline tide), due to alkalosis (in which the body’s pH is too high), or due to someurinary tract infections (in which certain bacteria can alter the urine’s pH). Decreased pH, causing acidic urine, can occur due to a high protein diet (such as a carnivore diet since meat contains a higher amount of protein than a diet with more grains and vegetables), acidosis (when the body’s pH is too low), or certain medication use (such as furosemide or Lasix®). The pH of urine is important to control since certain urinary stones (also known as uroliths or calculi) are more likely to form depending on your pet’s urinary pH. For instance, struvite stones form in alkaline urine while other types (such as dihydrate calcium oxalate stones) tend to occur in acidic urine. (For more information on alkalosis and acidosis, click here to read about TCO2.)
Protein: Protein detected in urine is termedproteinuria.In normal health, a largeamount of protein should not be found in urine. Urinary proteinmay come from three major sources: 1) pre-renal, 2) renal, and 3) post-renal. Protein of pre-renal origin means that the initialcauseis outside the urinary tract and may be due to fever, seizures, red blood cell destruction(i.e.hemolysis), and certain cancers (such as multiple myeloma). Damage to the kidneys can result in proteinuria of renal origin. The kidneys contain a cluster of blood vessels called glomeruli that hug around tubules (little tubes) in the kidney and act to removewaste products from the bloodstream to be filteredinto urine. Most protein molecules are too large to fit through tiny holes in the glomeruli (think of a sieve), so these proteins normally remain in the bloodstream, which is a good thing since they act as transporters, function in the immune system, and maintain normal liquid volume inside blood vessels (for more information on blood proteins, click here.)However, if glomeruli become “leaky” due to disease, their holes can enlarge and allow bigger protein molecules to seep out of the bloodstream and into urine. As more protein molecules try to squeeze their way out of glomeruli holes, they can damage the glomeruli further, starting a vicious cycle that allowsthem to “leak” even more and cause permanent and worsening kidney damage and possible failure. The severity of kidney disease can also be assessed by the relationship of proteinuria to USG. The higher the protein reading paired with the lower the USG (i.e. more dilute urine) = the worse the kidney disease. If too much protein leaks out of the bloodstream into urine (this disease process is known as protein-losing nephropathy), blood protein levels can become dangerously low, resulting in leakage of fluid into the abdomen or lungs as well as blood clotting disorders. In conclusion, causes of post-renal protein stem from infection, stones, bleeding, cancer*, or trauma to the urinary tract or genitalia. Occasionally, a false reading of protein on urinalysis can occur in alkaline urine. (*Note: If bladder or prostate cancer is suspected in your dog, your vet may consider running a noninvasive urine test called the CADET® BRAF gene test by Sentinel Biomedical.)
- Glucose: Glucose (i.e. “blood sugar”) is not normally found in the urine of healthy animals. The kidneys normally do a good job of keeping glucose in the bloodstream. However, if glucose levels rise too high (as in the cases of diabetes mellitus), the kidneys become too overwhelmed to keep all that glucose in the blood, so some leaks out into urine. In addition to diabetes, other causes of glucose detected on urinalysisinclude urine collection following a meal, pancreatitis, Cushing’s disease, severe stress, certain medications (ketamine, steroids), and kidney disease. Why is it bad to have persistent glucose in urine? Because bacteria and fungal organisms LOOOOOVE to get their sugar rush on by feasting on this excess glucose. Thus, urinary glucose provides a prime environment for the development of urinary tract infections (UTIs). This is why diabetic patients and those with Cushing’s disease can have recurrent or persistent UTIs.
- Ketones: Ketones are products formed from the metabolism of fat when the body does not have enough of its typical fuel source (carbohydrates, such as glucose) to be usedfor energy. Ketone formation can occur due to starvation (more typically seen in young animals), a high fat or low carb diet, or due to diabetes mellitus (in which the body’s cells do not have the capacity to normally utilize glucose, so fat ismetabolizedinstead).
- Bilirubin: Bilirubin is a waste product from red blood cells that is processed by the liver. When the body’s bilirubin level is elevated due to red blood cell destruction(hemolysis)or liver disease, it will spill over from the bloodstream into urine. In dogs, bilirubin will be detected on urinalysis before its elevation will be observedon bloodwork.(For more information on bilirubin, click here.)
- Blood: Red blood cells or their related products (such as hemoglobin and myoglobin) can enter urine due to hemolysis, blood clotting disorders, traumatic injuries, severe muscle injuries, urinary tract infections, or cancer.
- Sediment: Following the dipstick test, a small urine sample is spun down in a centrifuge to separate out any solid products (cells, crystals, etc.) from the liquid portion of urine. Any solid material that separates out is then placed on a microscope slide to be visually interpreted under magnification (or high power field, a.k.a. HPF).
- RBC/HPF: a.k.a. Red blood cells per high power field. Hematuria is the presence of red blood cells on urinalysis. Causes are as discussed above under “Dipstick.” Some degree of hematuriais to be expected following a urine sample collected via cystocentesis or catheterization.
- WBC/HPF: a.k.a. White blood cells per high power field. A high white blood cell count in urine is calledpyuria. The presence of white blood cells may be secondary to infection of the urinary tract or genitals, inflammation from urinary stones, or urinary tract cancers (such as transitional cell carcinoma, or TCC).
- Epithelial Cells/HPF: a.k.a. Epithelial cells per high power field. Some cells from the lining of the urinary or reproductive tracts may exfoliate off and enter a urine sample. Squamous epithelial cells from the urethra (the tube leaving the bladder to the outside world) or reproductive tracts are not usually worrisome if seen on urinalysis. Transitional epithelial cells from the urinary tracts may be normally seen in small amounts, but an abundance of the cells seen in the Sediment can occur secondary to urinary tract infections, stones, or cancer. Renal tubular epithelial cells may be seen in cases of kidney damage.
- Casts/HPF: a.k.a. Casts per high power field. Casts are little flexible clumps of proteins and cells that act like “papier-mâché” by molding into the exact shape of the kidney tubule from which theyoriginate. Some casts are not worrisome while others are suggestive of kidney damage.
- Crystals: Crystals are microscopicsolid particlesthat can form in urine either inside the bladder or inside a urine sample collection container if it sits out too long before urinalysis testing (especially in a refrigerator). Crystal formation is influenced by urine pH; for example, alkaline urine promotes the formation of magnesium ammonium phosphate (struvite) crystals while acidic urine allows for the formation of dihydrate calcium oxalate crystals.Some crystal typesmay also be an indication of larger urinary stones (such as struvite, uric acid, cysteine uroliths) or liver failure (ammonium urate crystals). One of the most alarming crystal shapes that a vet or her technician can see are monohydrate calcium oxalate crystals, which issuggestive of ethylene glycol (antifreeze) toxicity, which causes acute kidney failure and death.
- Bacteria: The presence of bacteria in the urine can indicate an infection of the urinary or reproductive tracts or may be secondary to contamination in the urine collection process. The presence of white blood cells (pyuria) along with bacteria on urinalysis is a higher indication of infection versus contamination. To remove the possibility of contaminants entering the urine sample, obtaining the sample by cystocentesis or catheterizationis ideal. If your pet has a difficult to manage urinary tract infection (UTI) or is prone to frequently recurrent UTIs (for instance, diabetic patients), your vet may also wish to gather a urine sample via cystocentesis and submit a urine culture to a specialty lab. Urine cultures help gauge the causative organism of the infection and aid your vet in determining which antibiotics to use.
- UPC ratio: The Urine Protein : Creatinine Ratio test is not run on every patient as it is not a part of a routineurinalysis. Up until recently, this specialized test had to be performed at an off-site laboratory; however, more and more general practice veterinary clinics now have capabilities of running a UPC in-house. The purpose of this test is to detect if protein found in urine is actually due to kidney leakage secondaryto renal damage (i.e. proteinuria of renal origin versus other sources of urinary protein). UPC is especially helpful in assessing function of the glomeruli in specific disease states, such as Lyme disease in dogs (cats are less likely to have disease to glomeruli). In the absence of red and white blood cells and bacteria (presence of these cells can falsely elevate the UPC reading), a high UPC ratio denotes significant kidney disease. A measurementof <0.2 is ideal.Tests related to UPC ratio include Sulfosalicylic Acid (SSA) (or Bumin Test) and Microalbuminuria measurement.
Sediment: Following the dipstick test, a small urine sample is spun down in a centrifuge to separate out any solid products (cells, crystals, etc.) from the liquid portion of urine. Any solid material that separates out is then placed on a microscope slide to be visually interpreted under magnification (or high power field, a.k.a. HPF).Click here to learn more about Lyme disease in dogs as well as the Lyme vaccine.
Pairing your new ability to interpret your dog or cat’s urinalysis with your knowledge of reading your pet’s bloodworkmakes you a Pet Mommy or DaddySuperhero! if you have further questions about your pet’s labwork results, feel free to contact us!
Check out our other articles on How to Interpret Your Pet’s Bloodworkas well as onFeline Lower Urinary Tract Disease (FLUTD),Urinary Tract Infections (UTIs), and kidney disease. And visit the sitelater for a future article on urinary stones.
– Maranda Elswick, DVM
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