Bloody urine – the list of differential diagnoses lengthens, but diagnostics remain the same

Summary The cause of haematuria often can be surmised based on a horse's signalment, recent history, and clinical signs that may accompany haematuria. The site, if not the cause, of haemorrhage can sometimes be revealed by examining that portion of the urinary tract palpable per rectum, by endoscopically examining the urethra and bladder, or by ultrasonographically examining the kidneys. When cystolithiasis or urethrolithiasis is determined to be the cause of haematuria, further examination is indicated to identify disease of one or both kidneys that might have precipitated formation of the urolith. Contrast‐enhanced, cross‐sectional imaging of the abdomen of small equids might be of value when a vascular anomaly of a kidney is suspected. Neoplastic cells can sometimes be found in the urine of horses suffering from neoplasia of the bladder or in peritoneal fluid of horses suffering from renal neoplasia. When a kidney is determined to be the source of haemorrhage, urine can be obtained for bacterial culture and cytological examination by passing tubing through the biopsy port of an endoscope into the ureter draining the kidney in question. Histological examination of tissue obtained by biopsy of the kidney or the mucosa of the bladder may be indicated when neoplasia of one of these organs is suspected. Immunohistochemical examination of endoscopically obtained tissue from a cystic carcinoma can identify whether the neoplastic cells express COX ‐2 receptors, thereby determining if treating the horse with a COX ‐2 selective NSAID might be effective.