The urinary system is comprised of the upper (kidneys and ureters) and lower urinary tracts (bladder and urethra). The kidneys' most important function is to filter waste from the blood. When this does not happen properly, waste products can build to dangerous levels in the blood, giving rise to azotemia. Evaluation of horses with kidney disease is performed via ultrasonography of these organs.
Evaluation of the bladder and urethra for the presence of stones (uroliths) or calculi is performed via endoscopic examination (cystoscopy). Uroliths are formed when minerals that naturally occur in urine clump together to form tiny crystals. These stones can develop anywhere in the urinary tract, including the kidneys, ureters, bladder, or urethra. The formation of uroliths is seen most frequently in adults. There is no one breed that is more prone to urolithiasis than another; however, it is seen more frequently in males than females.