Harold C. Schott II,
Hematuria
Hematuria can be the presenting complaint for a variety of disorders of the urinary tract. The problems causing hematuria can range from relatively minor disorders to more severe disease processes that may result in life-threatening hemorrhage. Urolithiasis, urinary tract infection, and neoplasia are some of the more common causes of hematuria. Other causes of hematuria include exercise-associated hematuria, proximal urethral tears in stock-type horses, idiopathic renal hematuria, and idiopathic cystitis.
Normal urine contains about 5000 red blood cells (RBCs)/mL or less than 5 RBCs/high-power field (hpf) on sediment examination. Microscopic hematuria (10,000 to 2,500,000 RBCs/mL) can be detected as an increase in RBCs on sediment examination (10 to 20/hpf) or a trace to +++ reaction on reagent strip testing of urine. It is important to recognize that reagent strip results, which use the peroxidase-like activity of hemoglobin and myoglobin to oxidize a chromogen in the test pad, do not differentiate between hemoglobin and myoglobin. Thus positive results are not specific for hematuria and may be more appropriately termed pigmenturia. Despite this limitation, reagent strips can be used to differentiate hematuria from hemoglobinuria or myoglobinuria when the color change is limited to scattered spots on the test pad. This pattern implies that intact RBCs were adsorbed onto the pad, underwent lysis, and produced a localized color change through hemoglobin activity on the chromogenic substrates. Macroscopic or gross hematuria can be observed with more than 2,500,000 to 5,000,000 RBCs/mL (about 0.5 mL of blood per liter of urine). Macroscopic hematuria can be differentiated from other causes of pigmenturia by centrifuging a sample of urine to produce a red cell pellet and clear supernatant urine.
Noting the timing of hematuria can be useful in localizing the site of urinary tract hemorrhage. Hematuria throughout urination is consistent with hemorrhage from the kidneys, ureters, or bladder, whereas hematuria at the beginning of urination is often associated with lesions in the distal urethra. Hematuria at the end of urination is usually the result of hemorrhage from the proximal urethra or bladder neck. A thorough diagnostic evaluation, including physical examination, rectal palpation, analyses of blood and urine, endoscopy of the lower tract, and ultrasonography, is usually rewarding in establishing the source and cause of urinary tract hemorrhage.
Urolithiasis
Uroliths at any level of the urinary tract may cause mucosal irritation and hemorrhage, resulting in hematuria. The classic presenting complaint for a cystolith in a gelding is postexercise hematuria, whereas horses with urethroliths may have incontinence or urinary obstruction and signs of colic, often with a dropped penis. Stones in both locations may also cause signs of painful urination, including stranguria and pollakiuria. Rectal examination is usually rewarding in confirming the presence of cystoliths, whereas urethroliths are commonly lodged at or just below the pelvic brim. The latter can be palpated externally, and the urethra above the obstructing urethrolith is often quite distended. When palpating for a suspected cystolith, the examiner should remember that dysuria and pollakiuria frequently result in a small bladder that may lie entirely within the pelvic canal. In this situation, the bladder and disk-shaped cystolith are best palpated with the hand inserted only wrist deep into the rectum. If the hand is inserted further forward to search for the bladder in the expected location over the brim of the pelvis, a cystolith can be missed because it may be lying just under the wrist or forearm. In contrast, the bladder may be markedly enlarged with an obstructive urethrolith.
Uroliths in horses are composed of calcium carbonate crystals, with varying amounts of phosphate, and are not amenable to dietary dissolution. Thus treatment of cystoliths consists of surgical removal, and a variety of procedures exist. During preparation for surgery, the author recommends collection of a catheterized urine sample for quantitative bacterial culture because concurrent urinary tract infection may accompany urolithiasis. In addition, either the entire stone or a portion of the cystoliths should also be submitted for culture after removal because recovery of bacteria is higher from stones than from urine samples. Nephroliths and ureteroliths carry a more guarded prognosis, especially with bilateral disease that results in chronic kidney disease, although removal by ureterotomy or nephrectomy can be an effective treatment in horses with obstructive unilateral disease.
Urinary Tract Infection
Urinary tract infection (UTI), although uncommon in horses, can cause hematuria. With upper UTI, partial anorexia, weight loss, and fever may be additional presenting complaints, whereas horses with cystitis generally manifest stranguria and pollakiuria. The author has also managed a handful of cases with unilateral pyelonephritis that developed recurrent urethrolithiasis. Diagnostic evaluation includes quantitative urine culture, renal ultrasonography, and endoscopic examination of the lower urinary tract. The occasional horse may have a bladder diverticulum or other anatomic defect that would predispose them to cystitis. Treatment consists of appropriate antimicrobial treatment and surgical removal of uroliths, when present.
Urinary Tract Neoplasia
Hematuria is the most common presenting complaint for neoplasia of the kidneys, ureters, bladder, or urethra. Adenocarcinoma is the most common renal tumor, and squamous cell carcinoma is the most common neoplasm of the bladder and urethra. Physical, rectal, laboratory, cystoscopic, and ultrasonographic examinations are usually rewarding in locating the neoplasm. Treatment is usually unsuccessful unless a focal neoplasm can be removed by nephrectomy or partial resection of the bladder. Neoplasms affecting the distal urethra (squamous cell carcinoma or sarcoid) may also be amenable to surgical resection and local antineoplastic therapy with 5-fluorouracil or cisplatin.
Exercise-Associated Hematuria
Exercise is accompanied by increased filtration of RBCs across the glomerular barrier. Typically, hematuria is microscopic, but gross discoloration of urine may occasionally be observed. Gross hematuria is likely a consequence of bladder mucosal erosions that are traumatically induced by abdominal contents pounding the bladder against the pelvis during exercise. A history of emptying the bladder immediately before a high-intensity exercise bout would increase the risk for developing this problem, as would prolonged low-intensity exercise (often referred to as “bongo drum bladder” in endurance horses). Although apparently nonpainful to the horse, owners of affected equine athletes are often quite concerned about gross hematuria after exercise. Detection of focal bladder erosions or ulcers with a contrecoup distribution during cystoscopy performed 48 hours after onset of hematuria may confirm this problem; however, a diagnosis of exercise-associated hematuria is often one of exclusion after diagnostic evaluation has ruled out other causes of hematuria, such as a cystolith. Exercise-associated hematuria is a self-limited problem because the bladder mucosal lesions heal within a few days.
