Overview
Definition:
Bladder catheterization refers to the insertion of a catheter through the urethra into the bladder to obtain a urine sample
In pediatrics, obtaining a sterile urine sample is crucial for diagnosing urinary tract infections (UTIs) and other urinary tract abnormalities
Two common methods are the clean-catch midstream urine (CCMSU) sample and a sample obtained via catheterization.
Epidemiology:
UTIs are common in pediatric patients, particularly in infants and young children
The incidence varies by age and gender
Accurate urine culture results are vital for guiding antibiotic therapy, preventing complications like pyelonephritis and renal scarring, and informing long-term management strategies.
Clinical Significance:
The choice of urine collection method significantly impacts the accuracy of urinalysis and urine culture results
Contaminated samples can lead to false-positive or false-negative results, resulting in inappropriate treatment, delayed diagnosis, or unnecessary investigations
Understanding the nuances of each method is critical for optimal pediatric patient care.
Collection Methods
Clean Catch Midstream Urine:
In older, toilet-trained children, this involves careful perineal cleansing followed by collection of a midstream urine sample
The initial stream of urine is discarded, and the sample is collected from the midstream portion
This method aims to minimize contamination from skin flora
Requires patient cooperation and careful technique.
Catheter Specimen:
In infants, neonates, or uncooperative older children, urine obtained by urethral catheterization is considered the gold standard for a sterile sample
A sterile catheter is inserted into the bladder through the urethra, and urine is directly aspirated
This method is invasive and carries a small risk of introducing infection.
Suprapubic Aspiration:
Although less common, suprapubic aspiration (SPA) involves inserting a needle directly into the bladder through the abdominal wall
This yields a sterile sample but is more invasive and typically reserved for specific clinical scenarios or when other methods fail.
Clean Catch Technique
Patient Preparation:
For toilet-trained children: Explain the procedure simply
Ensure adequate hydration for a good urine sample
For infants/non-toilet-trained: Perineal area must be thoroughly cleaned with soap and water, then rinsed and dried
A sterile collection device (bag or cup) is then applied to collect the voided urine.
Collection Process:
For toilet-trained: Have the child start voiding, discard the first part of the stream, then collect the midstream portion in a sterile container
For infants/non-toilet-trained: After cleaning, wait for spontaneous voiding and collect the urine in the sterile bag/cup
The bag should be removed immediately after voiding.
Potential Challenges:
Contamination is a major concern
Inability to collect a sample if the child does not void spontaneously
Difficulty in obtaining a true midstream sample
Inadequate cleaning of the perineal area.
Catheter Specimen Technique
Indications:
Infants and neonates unable to void spontaneously
Uncooperative older children
When a sterile sample is critical for diagnosis, especially suspected UTI in young infants
When CCMSU is unsuccessful or contaminated.
Procedure Steps:
Strict aseptic technique is paramount
Cleanse the perineal area thoroughly
Use sterile gloves and a sterile catheter of appropriate size
Lubricate the catheter
Gently insert the catheter into the urethra until urine flows
Collect urine in a sterile container directly from the catheter
Remove the catheter once the sample is obtained or after a short dwell time if required by protocol.
Risks And Complications:
Urinary tract infection (iatrogenic)
Urethral trauma or irritation
Pain or discomfort for the child
Bladder perforation (rare)..
Comparison And Choice
Accuracy And Contamination:
Catheterization generally yields a more sterile sample with lower contamination rates compared to clean catch, especially in infants
However, even catheterization carries a small risk of contamination if aseptic technique is not rigorously followed.
Age Appropriateness:
Clean catch is preferred for cooperative, toilet-trained children due to its non-invasiveness
Catheterization is often the method of choice for infants, neonates, and uncooperative older children where CCMSU is unreliable or impossible.
Clinical Context:
The decision depends on the child's age, developmental stage, ability to cooperate, and the clinical suspicion of UTI
In very young infants with high suspicion of UTI, catheterization is often the preferred first-line method for obtaining a reliable sample.
Investigations And Interpretation
Urinalysis:
Includes color, clarity, specific gravity, pH, protein, glucose, ketones, bilirubin, urobilinogen, leukocyte esterase, and nitrites
Pyuria (leukocytes >10/HPF) and bacteriuria (positive nitrites) are suggestive of UTI but not diagnostic alone.
Urine Culture And Sensitivity:
The gold standard for diagnosing UTI
Identifies the causative pathogen and its antibiotic susceptibility
A significant colony count (e.g., >10^5 CFU/mL for CCMSU or >10^4 CFU/mL for catheterized/SPA in symptomatic patients) is diagnostic
Interpretation varies based on collection method and symptoms.
Imaging Studies:
Renal and bladder ultrasound (RBU) and voiding cystourethrogram (VCUG) are often performed to evaluate for anatomical abnormalities or reflux in children with UTIs, particularly recurrent UTIs or those with pyelonephritis.
Key Points
Exam Focus:
Know the indications and contraindications for each method
Understand the potential for contamination with CCMSU vs
catheterization
Be aware of diagnostic cutoffs for urine culture based on collection method
Recognize the importance of sterile technique for catheterization.
Clinical Pearls:
For CCMSU in infants, apply the collection bag after cleaning and remove it promptly after voiding
Always label the specimen with the child's name, DOB, collection time, and method
For catheterization, use the smallest appropriate catheter size and maintain strict aseptic technique to minimize the risk of UTI.
Common Mistakes:
Using non-sterile containers or improper collection technique leading to contamination
Relying on UA findings alone without culture and sensitivity
Inappropriate antibiotic selection based on contaminated cultures
Delaying sterile sample collection in critically ill infants with suspected UTI.