Cystocentesis (ie, obtaining urine directly from the urinary bladder by inserting a needle through the body wall) is common and considered the ideal method for obtaining urine for urinalysis and culture and susceptibility testing.1 Cystocentesis typically helps prevent contamination (eg, from bacteria, RBCs, WBCs, or debris from the lower urinary tract and perineum) that can occur with voided or catheterized urine samples.2 Diagnosis of bacterial cystitis is somewhat simplified through cystocentesis, as samples through this method should be sterile3; quantitative bacterial counts should be analyzed when evaluating voided samples.4 Although frequently iatrogenic and self-limiting, hematuria may be noted in cystocentesis samples.5
The urinary bladder is located in the caudal abdomen and positioned within the pelvic inlet ventral to the colon. The urinary bladder may fall to the dependent portion of the caudal abdomen if the patient is in lateral recumbency. The ureters terminate in the dorsal aspect of the bladder at the trigone. The urinary bladder is primarily composed of striated muscle, and blood is supplied by cranial and caudal vesical arteries. When filled, the urinary bladder can be easily palpated in most patients; however, palpation may not be feasible in some obese patients or in patients with either a low volume of urine or anatomic abnormalities (eg, pelvic bladder).6
Indications for cystocentesis include collecting urine samples from patients for which a urine sample is needed. Most cystocentesis samples are used for urinalysis and urine culture and susceptibility testing. Other diagnostic tests may include urine protein:creatinine ratio, urine cortisol concentration, urine catecholamine concentration, urine leptospirosis PCR, and urine electrolyte concentration.
Cystocentesis may also be used therapeutically in patients that have urinary obstruction secondary to uroliths, urethral plugs, and/or neoplasia. Decompressive cystocentesis can alleviate patient discomfort prior to urinary obstruction removal and can lower intraluminal bladder pressure and facilitate retropulsion of urethral plugs/uroliths, potentially easing catheterization.7 Decompressive cystocentesis should be performed with an extension set and a 3-way stopcock to allow for a single needle insertion as opposed to multiple needle insertions. Although decompressive cystocentesis has previously been discouraged, studies have suggested there is minimal risk for bladder rupture/uroperitoneum.8
Cystocentesis is often performed with ultrasonographic guidance, although this is not required (ie, blind cystocentesis). Using ultrasonography can help direct visualization of the needle in the urinary bladder lumen, avoiding iatrogenic damage of surrounding structures (Figure 1). The relative size of the bladder, echogenicity of its contents, and any obvious structural abnormalities can also be observed. A primary advantage of blind cystocentesis is that it does not require special equipment. Cystocentesis can be challenging to perform in patients that have abdominal effusion and should be performed with ultrasonographic guidance in such cases.
Cystocentesis is usually performed in awake patients, but sedation should be considered in fractious or uncooperative patients. See Related Article for a full outline of a sedation protocol.