AVMA 2018: A Stepwise Approach to Investigating Hematuria in Dogs
Determining the cause of blood in the urine requires an organized method that includes a careful history, urinalysis, and more.
According to Jody Lulich, DVM, PhD, DACVIM, a professor in the Department of Veterinary Clinical Sciences at the University of Minnesota College of Veterinary Medicine in St. Paul, hematuria is a common presenting complaint in canine practice. And, although it has many possible causes, the most common originate in the urinary tract and include calculi, tumors (predominantly transitional cell carcinoma of the urinary bladder), and bacterial infection.
​However, presenting at 2018 AVMA Convention in Denver, Colorado, Dr. Lulich stressed the benefit of taking an organized approach to finding the cause of hematuria in small animals. "Just because you see blood in the urine, it doesn't mean it's from the urinary tract," he emphasized.
When presented with a patient with hematuria, Dr. Lulich advised veterinarians to first perform a urinalysis to determine whether the hematuria is due to hemolysis or hemorrhage. "This will also help you decide what test to do next," he said. "Red urine that is positive for occult blood and contains few red blood cells (RBCs) is consistent with hemoglobinuria or myoglobinuria," he added. "Obtaining a complete blood count and serum creatine kinase concentration will help determine the source and cause."
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A value of 0 to 5 RBCs seen microscopically per high power field (HPF) is typically considered within normal limits and thus points to hemolysis rather than hemorrhage as the likely underlying origin of the hematuria, he noted. In contrast, values greater than 0 to 5 RBCs per HPF increase the likelihood of underlying hemorrhage.
When considering hemolysis in dogs, this typically results from immune-mediated hemolytic anemia, oxidative damage to RBCs (commonly due to exposure to substances such as onions, garlic, vitamin K, and zinc), heartworm disease or, less commonly, congenital causes (such as phosphofructokinase deficiency). Careful questioning of the owner about the dog's clinical history can help veterinarians identify issues such as potential exposure to RBC oxidants or heartworm disease. Similarly, in cases of heartworm disease, microfilariae may be found in the blood, and even in the urine.
If the data point to hemorrhage, the next goal is to determine whether this is due to local bleeding in the urogenital tract or a generalized coagulation disorder, Dr. Lulich said. The presence of additional clinical signs can also help you differentiate between these two
options, Dr. Lulich said. For example, evidence of mucous membrane petechiation or skin bruising might be more suggestive of a generalized disorder, guiding you toward ordering a coagulation profile.
Local bleeding can arise due to damage to the kidneys, urinary bladder, or genital tract. Most commonly, this occurs in association with infection, trauma, cancer, or ischemia, he added.
Dr. Lulich also advised veterinarians to consider other features of the urinalysis that could prove helpful when investigating hematuria. He noted that if the red-discolored urine sample becomes clear after centrifugation, this indicates that the discoloration is due to the presence of RBCs; but if the urine remains cloudy and discolored, it is due to hemoglobin or myoglobin.
Always check the patient's urine specific gravity, too, he stressed, because this number provides more valuable diagnostic information. For example, he emphasized that if the specific gravity is greater than 1.040, in addition to ruling out kidney disease, this also helps to rule out diagnoses such as liver failure, hypercalcemia, diabetes mellitus, Cushing's disease, and Addison's disease. "Pay attention," he concluded, because the urine specific gravity can tell you a lot more than just about an animal's kidney function.
Dr. Parry, a board-certified veterinary pathologist, graduated from the University of Liverpool in 1997. After 13 years in academia, she founded Midwest Veterinary Pathology, LLC, where she now works as a private consultant. Dr. Parry writes regularly for veterinary organizations and publications.