Hematuria
Basic Information 
Epidemiology
Risk Factors
Horses fed alfalfa hay are at risk of developing hematuria caused by ingestion of blister beetles.
Clinical Presentation
History, Chief Complaint
• The history and chief complaints vary with the cause of hematuria.
• Renal Halicephalobus gingivalis infections: Hematuria plus concomitant neurologic disease and osteomyelitis
• Cantharidin toxicosis: Hematuria plus signs of abdominal pain and a recent history of ingesting alfalfa.
• Miscellaneous: Dehydrated horses treated inappropriately with nonsteroidal antiinflammatory drugs (NSAIDs) may develop hematuria. Hematuria is observed occasionally in exercising horses, especially if the bladder has been emptied immediately before exercise.
Etiology and Pathophysiology
• Hemorrhage into the urethral lumen through a urethral rent occurs when pressure in the corpus spongiosum penis (CSP) increases with contraction of the bulbospongiosus muscle to expel urine remaining in the urethra after urination.
• Exfoliated epithelial cells may act as a nidus for formation of cystic calculi in horses because some horses with urinary calculi have infection of the upper urinary tract.
• A severe, often fatal, idiopathic hematuria is reported to occur in primarily Arabian horses. Some clinicians believe that this condition is caused by pyelonephritis, which is a suppurative bacterial infection of the renal pelvis and parenchyma.
• Hematuria in horses may be caused by renal infection with H. gingivalis (previously known as Micronema deletrix), a saprophytic nematode.
• Renal and vesicular neoplasia. Adenocarcinoma (renal cell carcinoma) and lymphosarcoma are the most common tumors affecting the kidney, but adenocarcinoma is more likely than lymphosarcoma to cause hematuria. Squamous cell and transitional cell carcinomas of the bladder are also reported to cause hematuria in horses.
• Cantharidin, the toxic principle of blister beetles, is irritating to the digestive and urinary tracts. Irritation of the urinary tract may cause pollakiuria and hemorrhage of the urinary mucosa.
• Trauma to the umbilicus during the periparturient period with damage to the umbilical blood vessels may result in retrograde bleeding into the urachus and bladder and subsequent hematuria.
• Bacterial toxins or immune complexes may cause endothelial damage in glomerular capillary loops and small arterioles (glomerulonephritis), leading to renal failure, intravascular hemolysis, and renal hemorrhage.
• Chronic or excessive administration of NSAIDs causes decreased renal medullary blood flow that may result in medullary necrosis, leading to renal hemorrhage.
• Vascular anomalies, either congenital or acquired, are a rare cause of hematuria in horses.
• Repeated concussion of the bladder during exercise can be sufficient to cause mucosal damage and hemorrhage.
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