Hematuria, defined as the presence of red blood cells (RBCs) in urine, is a common clinical finding in both dogs and cats. Beyond simply identifying blood in the urine, the pattern by which RBCs mix with urine provides important clues regarding the anatomic source of bleeding. Careful observation of the urine stream during micturition can significantly narrow down differentials and guide diagnostic decisions.
Classification of Hematuria Based on RBC Mixing
Initial Hematuria
Initial hematuria refers to the presence of blood at the beginning of urination, followed by clearer urine as voiding continues.
This pattern strongly suggests a urethral source of bleeding, as blood located in the urethra is expelled first during micturition.
Common causes include:
- Urethritis
- Urethral trauma such as catheterization or mating injury
- Urethral uroliths
- Prostatic disease in male dogs
Terminal Hematuria
Terminal hematuria is characterized by clear urine initially, with blood appearing toward the end of urination.
This pattern indicates involvement of the urinary bladder or prostate, where contraction of the bladder wall at the end of voiding releases blood into the urine stream.
Common causes include:
- Bacterial or idiopathic cystitis
- Bladder urolithiasis
- Bladder neoplasia
- Prostatic disease in intact male dogs
- Feline lower urinary tract disease
Total (Complete) Hematuria
Total hematuria occurs when blood is uniformly mixed throughout the entire urine stream, resulting in consistently discolored urine from start to finish.
This pattern is most consistent with upper urinary tract bleeding, particularly the kidneys or ureters.
Common causes include:
- Glomerulonephritis
- Pyelonephritis
- Renal trauma
- Renal neoplasia
- Coagulopathies
- Acute or chronic kidney disease
Microscopic vs. Macroscopic Hematuria
Microscopic hematuria is detected only through urinalysis, with no visible change in urine color. It may be seen in early urinary tract infections, subclinical renal disease, or mild inflammation.
Macroscopic (gross) hematuria is visible to the naked eye and may appear pink, red, or tea-colored. This is commonly associated with more severe disease such as significant cystitis, urolithiasis, neoplasia, or trauma.
Clinical Interpretation Tips
- Uniformly mixed RBCs accompanied by proteinuria and urinary casts are highly suggestive of a renal origin of hematuria
- The presence of blood clots in urine typically points to a lower urinary tract source, as clot formation within the kidneys is uncommon
Conclusion
Hematuria should never be assessed as an isolated finding. Evaluating the pattern of RBC mixing in urine is a simple yet powerful clinical tool that helps localize the source of bleeding and refine diagnostic workups in both dogs and cats. When combined with urinalysis, imaging, and a thorough clinical history, this approach leads to more accurate diagnoses and better patient outcomes.
Dr. Geoff Carullo is a Fellow and the current President of the Philippine College of Canine Practitioners.
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