Urethral Obstruction & Urine Color in Male Cats

The most common causes of urethral obstruction (UO) in male cats are urethral plugs, uroliths, and idiopathic cystitis. Obstruction leads to increased pressure in the urinary bladder and urethra, which in turn may cause upper urinary tract disease, decreased glomerular filtration rate, and subsequent azotemia and hyperkalemia. Both the inciting cause and resulting urinary tract distension may cause hemorrhage and discolored urine. This prospective study sought to correlate gross urine color with clinicopathologic findings common in cats with naturally occurring UO.

Castrated cats (n = 75) that were presented for UO, catheterized, and had a lateral survey radiograph and lower urinary tract ultrasound were included. Urine color was scored based on a standardized chart (1 through 5: yellow, peach, pink, red, burgundy). Urinalysis, including dipstick and sediment examination, was performed. Darker urine color, significantly positively correlated with serum creatinine and potassium concentrations, was a significant predictor of azotemia. Additionally, urine color was significantly positively correlated with presence of red blood cells in sediment and blood on dipstick. Urine color was significantly negatively correlated with urine specific gravity. Urine color was not associated with presence or absence of crystals or lower urinary tract stones. These results suggest that cats with darker urine, which may indicate more significant metabolic changes, may require more aggressive supportive care during urinary catheter placement.

Global Commentary

The more time that passes between onset of urethral obstruction and establishment of urethral patency, the more likely there will be urinary bladder mucosal damage causing hematuria and postrenal azotemia or uremia. Prolonged urethral obstruction is also more likely to cause renal injury and decreased urine-concentrating ability. Although not evaluated in this study, it would be interesting to know if darker urine color at presentation is also associated with prolonged hospitalization or increased urethral obstruction recurrence rates. It should be emphasized that, although azotemia and hyperkalemia are more common in obstructed cats with dark urine, these metabolic derangements cannot be ruled out in obstructed cats with normally colored urine.—Gregory F. Grauer, DVM, MS, DACVIM (SAIM)

This capsule is part of the Global Edition of Clinician's Brief